energy efficiency building design guidelines for botswana

Energy Efficiency Building Design Guidelines

for Botswana

September 2007

Developing Energy Efficiency and Energy Conservation in the Building Sector, Botswana Project Funded by Danida

Department of Energy Ministry of Minerals, Energy and Water Resources

ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES

FOR BOTSWANA

September 2007

Developing Energy Efficiency & Department of Energy Energy Conservation Ministry of Minerals, Energy in the Building Sector, Botswana and Water Resources Funded By Danida

Author: Andreas Groth Acknowledgments: Jacob Knight of Arup Botswana wrote most of Section 8, Mechanical Systems, and made helpful comments on the other sections. Jesper Vauvert of Danish Energy Management A/S was the team leader for the project. He guided the preparation of the Guidelines

throughout and reviewed the document. A Task Force representing interested stakeholders reviewed the various drafts of the Guidelines as it developed and helped to guide the

process. The following were members of this Task Force:

o Mr. J. McCrory (Architects Association of Botswana) o Mr. A. Ntlhaile (Botswana Bureau of Standards) o Mr. M. Tafila (Association of Citizen Development Consultants) o Mr. T. Morewagae (Association of Consulting Engineers, Botswana) o Mr. N.Ofetotse (Botswana Housing Corporation) o Mr. E. Mazhani (Botswana Institute of Development Professions) o Mr. H.T. Tumisang (Botswana Technology Centre) o Mr. H.B. Brown (Department of Building and Engineering Services) o Mr. B. Kgaimena (Department of Energy) o Mr. G. Kumar (Department of Energy) o Mr. A. Groth (Department of Energy) o Mr. J. Vauvert (Department of Energy) o Mr. A. Sebinyane (Department of Housing) o Dr. Sajja (Department of Local Government and Development) o Mr. R.F. Rankhuna (Department of Town and Regional Planning) o Mr. F. Masuku (Gaborone City Council)

The project team for the project: Developing Energy Efficiency & Energy Conservation in the Building Sector, Botswana, and the staff

of the Department of Energy, Ministry of Minerals, Energy and Water Resources, Government of Botswana all gave their full support and encouragement in the preparation of this document. Danida funded the work (contract no.: 104 Botswana. 1.MFS.15).

Layout: The Guidelines has been formatted in landscape orientation in order to make it easy to read on screen as a pdf file. The font size and

scale for images have been chosen to allow it to be read at a scale that shows one page at a time. In print format the Guidelines is intended to be printed on both sides and bound on the left side of the odd pages. Comments and recommendations: Comments and recommendations for revisions should be sent to: Ministry of Minerals, Energy and Water Resources, Department of Energy, Private Bag 00378, Gaborone, Botswana Tel: +267 3914221, Fax: +267 3914201, email: [email protected], website:www.energyaffairs.bw or the author: Andreas Groth, Motheo (Pty) Ltd., P.O. Box 2224, Gaborone, Botswana, Tel: +267 3923462, Fax: +267 3923632,

email: [email protected] Published by Department of Energy © Department of Energy, Danish Energy Management A/S, and Motheo Pty. Ltd. All rights reserved, 2007 Printed in Gaborone, Botswana

REVISION TABLE

Revison No. Date issued: Sections Revised: Comments: 0 July 2007 All Original document, based on revisions to Draft No. 3 as presented at a

Workshop in Gaborone, Botswana on 7 March 2007. 1 September

2007 1, 2, 3, 4, 7, 8, 9, 10, 13 Amendments based on comments by Jacob Knight.

Additional properties of materials and elements.

SECTION 1 INTRODUCTION ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES FOR BOTSWANA Revision 1 September 2007

ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES FOR BOTSWANA Sections: 1. Introduction. 2. Design Brief. 3. Climate. 4. Indoor Environment. 5. Design and construction process. 6. Planning. 7. Building envelope. 8. Mechanical Systems. 9. Lighting - artificial and day lighting. 10. Operation & Maintenance and Building Management Systems. 11. Simulation. 12. Life-Cycle Cost Analysis. 13. Appendices.

Energy Efficiency Building Design Guidelines for Botswana – Section 1. Introduction Page 3

CONTENTS

1. INTRODUCTION 4

1.1. Background 4

1.2. Overview 4 1.2.1. Overall aim. 4 1.2.2. Classes of building. 5 1.2.3. Codes and Regulations. 5

1.3. Structure of the Guidelines 5 1.3.1. The Design Brief. 5 1.3.2. Technical Sections. 5

1.4. Who is the Guidelines intended for? 8

Energy Efficiency Building Design Guidelines for Botswana – Section 1. Introduction

1. INTRODUCTION

1.1. Background The project ‘Developing Energy Efficiency and Energy

Conservation in the Building Sector, Botswana’ was established in the Ministry of Minerals, Energy and Water Resources in 2005 to address the Government policy as stated in NDP 9:

“… Improving energy efficiency and conservation is cost

effective, offers a chance to defer new investment and helps reduce energy related pollution. During NDP 9, Government will continue to support and encourage improved energy efficiency and conservation in all sectors of the economy. Planned measures to achieve the policy objectives are: • Carrying out information and educational campaigns. • Conducting energy audits of energy intensive industries

and Government institutions • Promoting energy efficient design and operation of

buildings. • Developing and implementing a national energy

management plan.” One activity of the project was to develop guidelines for the

design of energy efficient buildings. This was done through a process of consultation with interested parties through a Task Force that has been established for this purpose.

It is expected that this document will need to be regularly

revised over the coming years to keep it up to date with

developments in the knowledge base and the regulatory environment of the building sector. The Guidelines and any subsequent revisions will be available as ‘pdf’ files on the website of the Department of Energy and the project website at http://www.eecob.com/.

1.2. Overview

1.2.1. Overall aim. The Guidelines is intended to be a resource that will help in

achieving the overall aim to improve energy efficiency and energy conservation in the building sector.

To achieve this, energy efficiency should be considered

from the beginning of the lifecycle of a building. This is typically the stage when the initial Design Brief is prepared For this reason the Design Brief has been chosen as the core document around which these Guidelines are structured.

Energy efficiency needs to be considered at every stage of

the lifecycle of a building. An optimum level of energy efficiency can be achieved when all aspects of the building design, construction and operation are integrated with each other in a coordinated manner to take full advantage of the opportunities that such synergies offer.

The Guidelines can assist in this by providing relevant

information and guidance on key issues related to the various stages in the life of a building from inception, procurement, design, construction, commissioning, operation, and ultimately decommissioning and demolition.


This will hopefully facilitate timely incorporation and consideration of those aspects early in the design process.

1.2.2. Classes of building. Requirements and opportunities for energy efficiency differ

in certain ways for different types of buildings. The first edition of the Guidelines is specifically directed at the following broad classes of building: o Office buildings. o Public facilities, such as Police Stations. o Health facilities, e.g. hospitals and clinics. o Schools. o Residential houses.

1.2.3. Codes and Regulations. At present the Codes and Regulations relating to buildings

in Botswana make little or no reference to energy efficiency.

In the absence of a specific Botswana code for energy

efficiency in buildings, building developers may wish to use the Guidelines as a tool to achieve energy efficiency in new buildings. This may be done by encouraging consultants to work in accordance with the recommendations of the Guidelines throughout the design and construction process.

It is the intention that the information and

recommendations contained in the Guidelines will be helpful in the development of an Energy Efficiency Code for buildings if and when this happens.

1.3. Structure of the Guidelines

1.3.1. The Design Brief. When the need for a building has been established, it is

good practice to prepare a Design Brief for the building. This should define all the requirements of the building, including the overall objectives that the building is intended to meet, the specific spaces that it will provide, their characteristics and relationships to each other, how the building will respond to its environment, constraints imposed by the site, the budget, the programme, and many other issues relating to the project.

A well-prepared Design Brief should guide the project

throughout the design and construction process. The client and the design team can use the Design Brief as a tool for monitoring the development of the project, to ensure that the original objectives and requirements are being achieved.

These Guidelines have been structured around the Design

Brief. The core document is Section 2, Design Brief. This sets out a suggested format for the Design Brief, and gives guidance for the preparation of each section of this suggesting how it can assist to enhance energy efficiency.

1.3.2. Technical Sections. The core document has deliberately been kept short and

simple, so that it can be useful to a wide variety of people. The more detailed and technical content relating to specific aspects of building design are included in Technical


Sections that are referred to in the relevant parts of Section 2, Design Brief.

The Technical Sections themselves also refer to other

reference material including Standards, Codes of Practice, books, papers, websites, etc. where relevant information may be found.

Section 13, Appendices provides data on the thermal

properties of materials and construction details, and other relevant information.


Technical Sections: 3. Climate.

4. Indoor Environment.

5. Design and construction process.

6. Planning.

7. Building envelope.

8. Mechanical Systems.

9. Lighting - artificial and daylighting.

10. Operation and Maintenance & Building Management Systems.

11. Simulation.

12. Life-Cycle Cost Analysis.

13. Appendices.


1.4. Who is the Guidelines intended for? It is hoped that the Guidelines will be of interest to all people involved in the process of procurement, design and operation of buildings. This includes the following groups of people:

Owners and developers.

o Building owners. o Developers. o Company employees with responsibility for property

development. o Government employees with responsibility for

property development. Planners and design consultants.

o Town Planners. o Landscape architects. o Architects. o Civil Engineers. o Structural Engineers. o Electrical Engineers. o Mechanical Engineers. o Quantity Surveyors.

People responsible for operation and maintenance of

buildings. o Facility Managers. o Property Managers. o Owners.

However it is specifically intended to be used by those involved in preparing and implementing the Design Brief. This includes the ‘client’ and the consultant team responsible for the design, construction and commissioning of the building.

SECTION 2 DESIGN BRIEF

ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES FOR BOTSWANA Revision 0 September 2007

Energy Efficiency Building Design Guidelines for Botswana – Section 2. Design Brief Page 3

CONTENTS

2. DESIGN BRIEF. 5

2.1. Project Objectives. 6

2.2. Project Requirements. 7 2.2.1. Schedule of accommodation. 7 2.2.2. Indoor environment specifications. 7 2.2.3. Lighting requirements. 8 2.2.4. Aesthetic considerations. 9

2.3. Opportunities and Constraints. 10 2.3.1. Siting. 10 2.3.2. Climate. 10 2.3.3. Budget. 11 2.3.4. Time. 11

2.4. Performance Targets. 12 2.4.1. Financial performance targets. 12 2.4.2. Energy performance targets. 12

2.5. Environmental Rating Schemes 13

2.6. Design Approach. 14 2.6.1. Procurement Strategy. 14 2.6.2. Integrated design approach. 14 2.6.3. Planning and landscape. 15 2.6.4. Envelope and structural design. 16 2.6.5. Lighting and electrical design. 19 2.6.6. HVAC design. 19

Energy Efficiency Building Design Guidelines for Botswana – Section 2. Design Brief

2.7. Operation and maintenance. 20

2.8. Resource Material 21 2.8.1. Books and reports. 21 2.8.2. Web resources 21

Energy Efficiency Building Design Guidelines - Section 2. Design Brief Page 5

2. DESIGN BRIEF. The Design Brief for a building project is essentially a

Terms of Reference for the project consultants, setting out the client’s objectives, requirements, constraints, targets and the design approach to be implemented in addressing these.

Typically the amount of thought and effort that is applied to

preparing the Design Brief varies enormously from one project to another, as does the amount of attention that is later paid to the document during the implementation of the project.

A well-prepared, accurate and comprehensive Design Brief

can make an important difference to the quality of the final building, and can also be a focus for ensuring that issues are raised and resolved before they become problems.

A well-prepared Design Brief can be used throughout the

project as a reference to ensure that the original objectives are achieved. It should be revised as necessary to reflect any changes that are agreed with the client.

The more competitive the procurement process for

consultants is, the more the pressure on them to reduce costs, and hence the need to verify performance against an agreed scope of work. A well-prepared, detailed design brief is a valuable component of the contract between a client and the consultants.

In the following sections, some key elements of a design

brief are considered with an emphasis on energy efficiency considerations.

A typical structure for a Design Brief is shown in the table

below.


2.1. Project Objectives. A description of the background to the project will be

followed by general statements of project objectives to indicate what is required from the project, and what is important to the client.

This will include the ‘direct’ objectives that have motivated

the client to initiate the project, e.g. the need for additional office space, a building that is needed to implement a business plan, or a new art department for a school.

It can also include indirect or secondary objectives that

relate to the client’s overall philosophy, or mission statement. These could include an emphasis on environmental sustainability, a desire to promote the local economy, or the wish to communicate a particular corporate identity.

A general statement could be included here relating to

energy efficiency, such as:

The development shall be designed to achieve an appropriate level of energy efficiency, taking into account life cycle costs and having due consideration for the likely increase in energy costs relative to other costs over the design life of the building.

DESIGN BRIEF - STRUCTURE Project Objectives. Project Requirements.

• Schedule of accommodation. • Indoor Environment requirements. • Aesthetic considerations.

Opportunities and Constraints. • Siting. • Climate. • Financial. • Time.

Performance Targets. • Financial • Energy

Design and Construction Approach. • Procurement strategy. • Integrated design approach • Planning and landscape. • Envelope and structural design. • Lighting and electrical design. • HVAC design. • Operation and maintenance considerations.


Similar statements may be included for other environmental considerations, such as water management, waste management, etc.

2.2. Project Requirements. This section will contain the specifications for the building

and other developments. The actual structure and content will vary depending on the type of development that is required.

2.2.1. Schedule of accommodation. The schedule of accommodation will indicate the main

types of space that are required, how large they need to be, and any particular requirements related to the use of each space.

It is also helpful define as far as possible the way in which

different spaces should relate to each other.

2.2.2. Indoor environment specifications. The primary requirement is likely to relate to the comfort of

the building’s occupants. Specifications for comfort are considered in more detail in Section 4, Indoor Environment. They should include consideration of the types of activity for which the building is intended.

Comfort conditions are affected by the overall approach to

air conditioning. Different specifications may apply to buildings that are mechanically air conditioned than to those that are naturally ventilated. Initially both specifications could be included, so that the decision on air conditioning approach may be delayed.

With regard to energy efficiency, it is important that the

specifications are appropriate to the actual needs of the building. An unduly restrictive specification may result in higher capital and recurrent cost as well as increased energy consumption.

The specification may also indicate the period of time for

which the specifications could be exceeded. If the indoor temperature exceeded the limit for say one week of the

TYPICAL INDOOR ENVIRONMENT SPECIFICATIONS Fresh air to achieve required air quality: o Air volume 8 – 12 litres/second/person o Air changes Min. 0.5ACH Temperature: Air conditioned buildings o Summer 23-27°C o Winter 20°C min Naturally ventilated / evaporatively cooled buildings o Summer 22-29 °C o Winter 19-26 °C Relative Humidity: o Maximum 80%


year, this may not cause great problems, but could result in a substantially smaller capacity HVAC system, with savings in energy consumption as well as capital and recurrent cost

Requirements for air quality should also be considered, as

these will affect the need for ventilation. Again, unnecessarily demanding specifications will lead to increased cost and energy consumption.

2.2.3. Lighting requirements. Lighting requirements should be specified in the Design

Brief, as well as some indications of the approach to be taken in the design of lighting.

Lighting levels required in different areas or rooms should

relate to the intended use of these spaces. Section 9, Lighting – artificial and daylighting gives indications of typical specifications for light level for different activities, as well as references to various standards and codes that provide more detailed information.

TYPICAL INDOOR LIGHTING REQUIREMENTS Public spaces – no visual tasks 50 lux Background lighting, offices 150 lux Task lighting, office work 300 lux Task lighting, detailed work 750 lux Task lighting, very fine work 3,000 lux


2.2.4. Aesthetic considerations. One of the greatest challenges in improving energy

efficiency in public and commercial buildings is to develop an architecture that is both aesthetically satisfying, and meets the technical requirements determined by the local climate and available material options.

It is important to set clear objectives regarding how the buildings should look, and to understand the implications on energy performance, initial cost and life cycle cost.

If it is regarded as an important objective for the building

that it makes a particular architectural statement, then the cost, energy and other implications should be clearly stated and agreed to.


2.3. Opportunities and Constraints.

2.3.1. Siting. If the client already has a site for the project, then an

assessment should be made of opportunities and constraints of the site that are relevant to the project. These are discussed in more detail in Section 6, Planning.

Energy considerations will include the orientation of the

site in relation to the sunpath and typical wind directions, shading features such as trees, hills, other buildings, and other factors affecting the local climate such as vegetation, ponds / rivers, wind breaks, etc.

2.3.2. Climate. The energy performance of a building is largely determined

by how well the design is adapted to the local climate. It is therefore important that the design team has a clear

understanding of the local climate with its daily and seasonal variations.

During the course of a year the climate changes with the

seasons, and there are also variations in climate from one year to the next. It is therefore necessary to define the climate for a typical year for use in building design.

Fig. 2.1 DB Temperature in Gaborone, by month. Fig. 2.2 Relative Humidity in Gaborone, by month.

RH DATA MONTHLY GABORONE 2000-2002

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

MONTH

RH

%

MINMAXAVG

TEMP DATA MONTHLY GABORONE 2000-2002

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0


MONTH

DEG

C

MINMAXAVGMAXDIFF


An assessment of the variation in climate for different

locations in Botswana suggests that for purposes of building design at least two climatic zones should be considered. The northern zone includes Chobe District and Ngamiland District. The southern zone includes all the remainder of the country.

Generally the winters in the northern zone are sufficiently

mild that there is little or no requirement for heating in buildings. In the southern zone heating in the winter is generally required, and may require more energy than summer cooling, depending on the building design and the amount of heat generated by activities in the building.

Maun has been taken as a typical location in the northern

zone, and Gaborone as a typical location in the southern zone. For each of these locations, the most relevant climate parameters have been determined for each hour of a typical year.

Any particular features of the local climate should be noted,

such as dominant wind direction, shading effect of any tall trees, hills or buildings, etc.

Further details are included in Section 3. Climate.

2.3.3. Budget. Opportunities and constraints regarding the financing of the

project should be considered at this stage. The chapter on

Project Cost and Energy Efficiency in Section 5, Design and Construction Process is relevant here.

Possible trade-offs between initial cost and life-cycle costs

may affect the way the project is financed. If access to capital finance is restricted this may reduce the scope for investment choices that will reduce life cycle cost. Section 12, Life-Cycle Cost Analysis gives a background to the methods that can be used to analyse various options and determine the most cost effective solution based on assumptions regarding future energy costs, maintenance interventions and other relevant parameters

It may be cost effective to invest in additional work and

cost in the design stage in order to optimise the energy performance of the building. The anticipated costs and benefits should be carefully considered.

2.3.4. Time. The client’s particular requirements regarding the project

programme should be defined. This may then be subdivided into pre-contract and post-contract programmes, to determine the amount of time available for the design process.

Detailed analysis of different approaches with regard to

energy efficiency takes time to carry out. The costs, both in consultant fees and project timing need to be considered and evaluated in relation to the opportunity to achieve a more cost effective and better quality project.


2.4. Performance Targets.

2.4.1. Financial performance targets. A building represents a substantial, long-term investment

by the owner. In many cases an important objective in making this investment is to obtain a financial return, either in the form of rental income, or saving of rental expense that would otherwise be incurred in the case of owner-occupied buildings.

It is therefore helpful to establish financial performance

targets for the building against which actual performance can later be assessed. This will also inform decisions made during the design phase of the project, and guide the Quantity Surveyor in making recommendations regarding the cost of different components.

The financial performance targets should be broken down

into capital costs, recurrent costs and recurrent income. These figures may if appropriate be developed into a life-cycle performance model to show the long term return on investment and predicted cash flows for the project.

2.4.2. Energy performance targets. An important element in the financial performance of a

building is energy cost. This requires estimates of the energy consumption for different purposes, as well as estimates of the price of different energy supplies. The major energy source for the types of building under consideration in these Guidelines is electricity. The cost of electricity is subject to change based on the changing

conditions of supply and demand, as well as the policies of the authorities that set the price.

In many countries codes and standards for energy

performance of buildings have been introduced. In some cases these are voluntary and give guidance to investors regarding what can be achieved. They can be used as specifications that the design team is expected to achieve, with or without financial incentives (see Section 5, Design and Construction Process )

Information regarding the actual energy performance of

different types of building in Botswana is becoming available through the work of the EECOB project in the Department of Energy, both through audits of existing buildings and simulations of typical ‘generic’ building types.

The following figures for specific energy consumption

(energy consumption per unit area) may be used as targets in the interim until actual energy performance standards become available.


Specific annual energy consumption [kWhr/m2.yr] Building type Total Lighting HVAC Office

EquipmentOther

Office 150 34.5 63 43.5 10.5 School 40 14.8 3.6 2.8 18.8 Residential (high cost, air conditioned) 89 21.4 23.1 0 44.5

2.5. Environmental Rating Schemes In many countries, environmental ratings are being adopted

by private clients and governments as a way of demonstrating that they are environmentally responsible. Well known rating systems include BREEAM (Building Research Establishment Environmental Assessment Method) and LEED (Leadership in Energy and Environmental Design). A client may make it a part of their brief that their building should achieve a BREEAM "excellent" rating, or a company may make it part of its sustainability policy that any new buildings which it procures will be constructed to achieve a BREEAM "very good" rating. For example, in 2003, the UK government made it a condition that all government departments when undertaking new or refurbishment projects carry out an environmental assessment, and that all new build projects must achieve a BREEAM "excellent" and refurbishment projects a "very good" rating.

These ratings consider a wide range of factors and compare

them against a local benchmark of "typical" construction practice. They can therefore be adapted to any country, although there are initial costs involved in establishing suitable local benchmarks, particularly if there are no regulatory requirements as in Botswana.

The BREEAM rating assesses the following:

o management: overall management policy, commissioning, site management and procedural issues such as controlling noise, dust and waste materials on the construction site.

o energy use: operational energy and carbon dioxide (CO2 ) issues such as the predicted energy use of air conditioning systems.

o health and well-being: indoor and external issues affecting health and well-being such as provision of

Table 2.1. Specific energy consumption targets by building type.


adequate daylight, artificial lighting and good air quality.

o pollution: air and water pollution issues, such as use of refrigerants, pollution from coal fires etc.

o transport: transport-related CO2 and location-related factors, such as availability of public transport links to the building and whether occupants are encouraged to use alternative forms of transport to private cars.

o land use: greenfield and brownfield sites, whether the project is a refurbishment or built on a site already developed, or whether it is built on virgin ground.

o ecology: ecological value conservation and enhancement of the site, including landscaping etc.

o materials: environmental implication of building materials, including life-cycle impacts.

o water: consumption and water efficiency.

Credits are available under each of these headings, and the total number of credits obtained determines the final score achieved (from Pass to Excellent).

2.6. Design Approach.

2.6.1. Procurement Strategy. There are a number of different procurement strategies that

can be used for the appointment of the professional team and the contractors for a building project.

These have implications for the energy performance of the building, which are discussed in more detail in Section 5, Design and Construction Process.

The most appropriate approach for a particular project

should be determined based on the priorities and resources of the owner.

2.6.2. Integrated design approach. A simple building such as a low cost residential house can

be fully designed by a competent, experienced designer such that all aspects of the building work well together in a coordinated, sensible way. The designer takes into consideration decisions that relate to one aspect of the building when making decisions on other aspects.

Since the same person is making all the design decisions,

she or he can easily consider the implications of a decision about say the location of windows on the planning of the rooms and the switching of lights.

Larger, more complex buildings require a team of

specialised designers, each working on different aspects of the overall design. Often they work for different firms located in different places, with limited communication. They will be coordinated by a team leader, often the architect or project manager, who is responsible for ensuring that the different elements of the building work in relation to each other.

Typically energy efficiency has not been a key

consideration in building design, and as a result the added


requirement of ensuring that the different design aspects work together to achieve optimum energy efficiency has tended to be overlooked.

By deliberately adopting an integrated approach to energy

efficient design, the design team can be encouraged to take advantage of opportunities to achieve improved energy performance.

This is discussed in more detail in Section 5. Design and

Construction Process. The integration of the different design aspects almost

always requires that changes in approach be made in each aspect to accommodate the others. Such changes should be

made as early in the design of the building as possible, since the time and work required in making changes increases rapidly as the design becomes more detailed.

It is helpful therefore to have a systematic approach to the

coordination of these approaches, and the Design Brief is a good opportunity for providing this. It is suggested that some initial indications are included in the Design Brief at the project inception stage, and that the consultants amend these as the design develops.

2.6.3. Planning and landscape. The planning of the building on the site provides many

opportunities for improving energy performance. The overall approach to energy performance should be

considered, e.g. whether the building will require


mechanical systems to control the indoor climate, or whether passive heating and cooling approaches will be used. In practice a combination of these may often be appropriate. Different solutions may be needed for different types of building. For buildings such as residential houses and classrooms it should be possible to achieve the required comfort levels with little or no mechanical equipment. In office buildings comfort conditions can be achieved with passive methods for much of the year, but some form of mechanical cooling may be required to deal with summer conditions.

The overall shape of the building is important to achieving

energy efficiency. It has been found that the walls perform an important role in removing heat from a building, suggesting that a high surface area to volume ratio is useful. This also allows for maximum use of daylight, reducing the energy needed for lighting, and indirectly helping to keep the building cool as well, since artificial lighting also generates heat.

Plants can be used very effectively to amend the local

climate on site, e.g. using trees for shade and wind breaks, ground cover to reduce reflected heat, climbing plants on frames to provide shade and evaporative cooling, etc.

Planning and landscaping are discussed further in Section

6, Planning.

2.6.4. Envelope and structural design. The building envelope consists of all the different elements

that make up the fabric of the building, such as the floor, walls, windows and roof.

Most of the design decisions relating to the building

envelope are the responsibility of the architect and structural engineer. They have a large impact on the thermal performance of the building, and it is therefore essential that the performance of the envelope is coordinated with the design of the HVAC system.

This is the area that offers most opportunities for improved

building performance through an integrated design approach.

Energy codes and standards for buildings typically specify

the performance requirements for the building envelope in terms of an ‘overall thermal transfer coefficient’ (OTTC), which gives an indication of the amount of heat that will flow between the building and the environment. In some cases the standard defines the requirements for the thermal properties of different building elements.

Typical values for the total thermal resistance of the walls

and roof proposed for the South African Standard SANS 283 and 204, The Energy Efficiency Standards are given in Table 2.2.


Building Element

Total ‘R’ value [m2.K/W] Total ‘U’ value [W/m2.K] Typical construction to achieve this value:

Wall Min. 1.4 Max. 0.71 Sand-cement brick cavity wall with 25mm insulation in cavity plastered both sides.

Roof and ceiling

Min. 2.7 Max 0.37 Galvanised roof sheets, 100mm insulation and 6mm ceiling.

Table 2.2. Thermal properties of building envelope elements (draft SANS 204) Source: TIASA. Frequently energy codes offer an alternative method of

demonstrating compliance based on a computer simulation of the proposed building using approved methods to verify whether it achieves the required minimum standard of performance.

Details regarding computer simulation of building energy

performance are provided in Section 11, Simulation. Windows and other glazing elements are frequently

responsible for more heat gain and loss than any other building element. Assuming that the roof is insulated to the level recommended in Table 2.2, the greatest source of solar heat gain in most buildings will be glazing. Glazing however also provides the opportunity to admit natural daylight into the building, reducing the energy consumption for artificial lighting. It is therefore important to achieve an optimum balance whereby the opportunity for effective daylight is achieved with minimal unwanted solar heat gain.

2.6.4.1. Summary of simulation results. Simulations of three building types; Classroom, Residential

and Office have been carried out for the Gaborone climate to quantify the effect on energy consumption of various alternative envelope and operational parameters.

Some of the key results are summarised below. In each case

references to changes in energy cost refer to total heating and cooling energy, not total building energy. Full tables of results are included in the EECOB Report: ‘Parametric simulation of the energy performance of three generic building types in Gaborone, Botswana’.

Orientation: Orientation in the N-S direction resulted in a 6% increase in

energy consumption over an E-W orientation for the classroom type of building. For the office it was only 0.8% and for the residential house it was 1.8%. This suggests that orientation is less significant than expected. However local effects within the building and impact on quality of daylight are also important considerations that are strongly related to orientation. It is therefore recommended that an


E-W orientation be used whenever possible, particularly where daylight is an important consideration as in offices and classrooms.

Roof: In the classroom building a white roof reduced energy by

45% compared to a galvanised roof with no ceiling insulation in both cases.

In the residential building, with ceiling insulation the white

metal roof is comparable in performance to a concrete tiled roof also with insulation.

In the three storey office building, a white metal roof

reduced energy consumption by 5% compared to a green coloured metal roof.

The addition of 100mm insulation on the ceiling reduced

energy consumption by 43% in the classroom (galvanised roof), 2.7% in the residential house (tiled roof), and had no effect in the office building (green metal roof).

Wall. An insulated cavity wall in place of a standard 220mm

solid wall increased energy consumption by 8% for the classroom and by 5% for the office. However it reduced energy consumption by 27% in the residential building. This energy saving was due to reduced heating cost. The insulated cavity wall was almost three times as effective as an uninsulated cavity wall, so the small extra cost of providing insulation in the cavity is well rewarded.

A 500mm wide mass wall with insulation on the inside gave similar results, with energy cost increased by 10% for the classroom and 7% for the office. In the residential house the energy saving increased to 30% compared with the insulated cavity wall.

The simulation showed that the walls provide some cooling

during the day when they absorb radiant heat from the ceiling. A width of 220mm seems to be about optimum; 115mm walls are worse, as are wider walls.

The simulation confirmed that different solutions are

appropriate for different types of building. Solid 220mm walls are best for classrooms and offices that are primarily occupied during the day, and insulated cavity walls or mass walls are effective for residential houses that are occupied more during the night.

Floor. The ground floor is also an important cooling element in all

buildings in summer, and also in winter for office buildings that require cooling all year. For the classroom, providing floor insulation resulted in a 23% increase in annual energy cost. In residential buildings there is some unwanted heat loss to the ground floor in winter, but this is marginal compared to the benefit in summer.

Windows. Heat flow through the windows from direct and indirect

solar radiation is in many cases the largest source of heat gain to the building. The easiest way to reduce this is to reduce the size of windows to the minimum required to


provide daylight and views. It was found that a glazing ratio of 20% (window to wall area) provided more than enough daylight in the classroom.

Ventilation. The use of ventilation to control indoor temperature was

found to be highly effective in the office building, resulting in a 28% energy saving. It was less effective in the residential house (11% saving) and in the classroom (2% saving). This should be considered as an option for office buildings, and would need to be included in the HVAC design approach, as it may require increased duct sizes, larger fans, and different control systems. It appears that the substantial savings that can be achieved would justify this extra expense.

Further suggestions for appropriate design approaches for

different building envelope elements are described in Section 7, Building Envelope.

2.6.5. Lighting and electrical design. Optimal use of daylight can result in reduced energy

consumption, and also has other benefits. Studies have shown that people perform better under daylight than artificial light. Views of the world outside the building are also important for the well-being of the occupants, and have been found to improve performance and productivity.

There are a number of opportunities to improve the

effectiveness of daylight without excess heat gain, including use of light shelves, light tubes and skylights.

The design of artificial lighting should aim to provide an adequate level of background illumination for general purposes, with higher levels of task lighting in the specific areas where more light is needed. This results in energy savings and also allows for more flexibility should the use of spaces change in future.

Control of lighting should be designed to ensure that lights

are only on when and where they are needed. This is discussed in more detail in Section 9, Lighting –

artificial and daylighting.

2.6.6. HVAC design. The mechanical systems or HVAC (heating, ventilation and

air conditioning) are designed to amend the indoor climate of a building to achieve the requirements of the particular application in buildings for which this cannot be achieved using natural ventilation alone.

The first decision that is required is therefore whether such

systems are required or not. This depends on how stringent the indoor environment requirements are, the internal loads from occupants and equipment, the local climatic conditions and the design of the building envelope.

If an HVAC system is required, the design approach should

be coordinated with the envelope design to ensure that the building requirements are achieved with an optimal energy performance.


It has been found that HVAC systems designed using hourly computer simulation are more accurately matched to the needs of a particular building in relation to the local climate than those designed using steady state methods.

It is recommended that for all projects that will have a

centralised HVAC system installed, computer simulation be used to determine the system capacity that is required.

Use of ventilation to control indoor temperatures offers

substantial energy savings, particularly in buildings with high heat gains from occupants, equipment and lighting. It is recommended that centralised HVAC systems be designed to use ventilation for this purpose as well as providing adequate indoor air quality.

In many situations it may be possible to achieve the

required comfort conditions using evaporative coolers in place of air conditioning systems, with far lower recurrent cost and energy consumption.

Further information is included in Section 8, Mechanical

Systems.

2.7. Operation and maintenance. The decisions that are made during the design phase of a

building have implications for how it will be operated and maintained.

The overall approach to operation and maintenance should

be specified in the Design Brief, so that this can guide the decisions taken in the design process.

In particular, the human resource requirements for the operation and maintenance of the building should be considered.

The Design Brief should specify the requirement for the

design team to prepare a draft Operations and Maintenance Manual as one of their tasks. This should be developed as an ongoing process during the design, to ensure that the O&M implications are given consideration

The draft O&M manual will then be revised and finalised

during and following the commissioning of the building. Possibly the greatest opportunity for reducing energy

consumption in buildings, and certainly the cheapest and quickest to implement is to encourage occupants to turn off lights and other equipment when these are not needed. The simulation of the office building indicated that 39% of total energy use could be saved through such behaviour change.

Operation and Maintenance considerations are discussed in

more detail in Section 10, Operation & Maintenance and Building Management Systems that also includes a suggested format for an O&M Manual.


2.8. Resource Material

2.8.1. Books and reports. TIASA, The Thermal Insulation Guide for Energy Efficiency in

Buildings. Thermal Insulation Association of Southern Africa. January 2006.

EECOB Report: ‘Energy Efficiency and Energy Conservation in the

Building Sector, Botswana, Report on Baseline Energy Surveys’, Department of Energy, Government of Botswana, July 2005.

Bauer, C. and Groth, A. EECOB Report: ‘Parametric simulation of

the energy performance of three generic building types in Gaborone, Botswana’. Department of Energy, Government of Botswana, January 2007.

2.8.2. Web resources BREEAM Building Research Establishment Environmental

Assessment Method http://www.breeam.org LEED Leadership in Energy and Environmental Design. http://www.usgbc.org/leed

SECTION 3 CLIMATE ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES FOR BOTSWANA Revision 1 September 2007

HOURLY AVERAGE TEMPS GABORONE 2000-2002

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Energy Efficiency Building Design Guidelines for Botswana – Section 3. Climate Page 3

CONTENTS

3. CLIMATE 5

3.1. Overview 5 3.1.1. Climate of Botswana. 5 3.1.2. Elements of climate. 5 3.1.3. Climatic zones. 5 3.1.4. Climate patterns. 5 3.1.5. Climate and simulation. 5

3.2. Climate of Botswana 6 3.2.1. Classification. 6 3.2.2. Cycles of climate and global warming. 8

3.3. Elements of Climate 9

3.3. Elements of Climate 10 3.3.1. Meteorological data 10 3.3.2. Temperature 10 3.3.3. Design Day Conditions 12 3.3.4. Humidity 13 3.3.5. Radiation 13 3.3.6. Wind 14 3.3.7. Rainfall 15

Energy Efficiency Building Design Guidelines for Botswana – Section 3. Climate

3.4. Climatic Zones. 15

3.5. Climate Patterns. 18

3.6. Resource Material 19 3.6.1. Books and papers 19 3.6.2. Web resources 20

Energy Efficiency Building Design Guidelines – Section 3. Climate Page 5

3. CLIMATE

3.1. Overview This Section addresses the subject of climate and its impact

on building energy performance in Botswana. The topics that will be covered are briefly outlined below.

3.1.1. Climate of Botswana. The section begins with an overview of the climate of

Botswana in a global context. The classification of the climate is considered, and various cycles in the climate are identified.

3.1.2. Elements of climate. This section includes a general discussion of the principal

elements of climate and how they relate to building energy performance. The ways in which data are collected and made available are also considered.

3.1.3. Climatic zones. The variation in climate with location is considered, with

particular reference to the implications for building energy performance. It is recommended that the country be divided into two climatic zones for the purposes of these Guidelines.

3.1.4. Climate patterns. In addition to the geographical variations in climate, there

are also patterns of climate within one locality. In considering the impact of climate on building energy performance, it is important to consider the different patterns that occur, and differentiate these from the average characteristics, which may never be experienced.

3.1.5. Climate and simulation. Building energy performance may be predicted using

software that simulates the interaction of the building with the climate.

Typical meteorological year data has been prepared for

Gaborone and Maun, which have been taken as typical of the Northern and Southern climate zones.

This data is available in a format that may be used for

computer simulation of building energy performance.


3.2. Climate of Botswana

3.2.1. Classification. In the Köppen Climate Classification System, the climate

of most of Botswana falls in the classification ‘BSh: semi-arid steppe, hot’. The exception is the extreme north of the country, which is classified, as ‘Aw: tropical wet-dry (low sun dry) – savanna’. Approximately two thirds of the area of the country is within the tropics. The Tropic of Capricorn crosses the Jwaneng - Ghanzi road just north of Kang, runs through the middle of Khutse game reserve, and crosses the Gaborone - Francistown road just north of Dibete.

Generally Botswana experiences a very high proportion of

clear, sunny days, with little cloud cover or rain. The summers are warm to hot in the day and cool at night,

particularly in the southwest of the country. Rainfall generally occurs in the time between October and April, which coincides with the summer months.

Winters are warm in the day and cool at night, with

minimum temperatures lower in the south, and increasing as one moves further north.

Summer maximum daytime temperatures are closely

related to rainfall, rising rapidly in times of drought. In years of reasonable rainfall, the highest average maximum temperature often occurs in October, before the rain begins, after which temperatures drop due to increased cloud cover

and evaporative cooling from the moisture in the soil. In years of drought, and in regions that receive less rain the maximum temperatures continue to rise until January or February.

Botswana is completely landlocked, and is located in the

centre of the southern African plateau. The country is approximately equidistant from the Atlantic Ocean coast, 1,000km to the west, and the Indian Ocean coast about 960km to the east (measured to the middle of the country). The country is relatively flat, at an average elevation of approximately 1000m above sea level. As a result moist air from the oceans seldom reaches Botswana without having first shed its moisture on the escarpments between. The distance from the ocean together with the relatively high altitude result in low, intermittent and unreliable rainfall. The rain that does occur is a result of localised regions of low pressure that draw in moist air from the coast.

Not only is the average rainfall in Botswana low, it is also

very variable, both within a particular year, and from one year to the next. There is a trend for average rainfall to reduce and variability to increase from north to south, and from east to west.


Fig. 3.1 Koppen climate classification.


3.2.2. Cycles of climate and global warming. A number of different climatic cycles have been observed,

including a short-term cycle of about 6-10 years during which a few years of good rain are followed by years of below average rain or drought. This takes place within the framework of a longer cycle spanning several centuries, and another even longer cycle of several thousands of years. Although the Kalahari has generally been a semi-arid area for millions of years, during that time there have been periods of sufficient rainfall to maintain large inland seas and perennial rivers that now remain as fossil river valleys.

Over the past century the natural long-term climatic cycles

of the earth have been subject to increasing influences from human activity, particularly the enormous increase in energy consumption from fossil fuels and resulting emissions of carbon dioxide. This has resulted in increased concentrations of greenhouse gasses in the atmosphere. These act as a radiation filter surrounding the earth, which allows solar radiant heat to pass through, but reflects thermal radiant heat back to the earth, as does the glass in a greenhouse. The consensus view of the Intergovernmental Panel on Climate Change (IPCC), the world authority on global warming, is that this could result in an increase in average temperatures over southern Africa of between 2-5°C over the coming century. The following excerpt from an article by Mike Davis in The Science News suggests that this may be a highly optimistic view.

The actual rate of change of climate may not be accurately

predictable, but there seems to be little doubt that increases

in temperature will be experienced throughout this century, together with increased energy cost, both in economic and environmental terms. This makes it even more urgent that buildings are designed and built to achieve human comfort with minimal energy consumption.


The Science News

Scientific discussions of environmental change and global warming have long been haunted by the specter of nonlinearity. Climate models, like econometric models, are easiest to build and understand when they are simple linear extrapolations of well-quantified past behavior: when causes maintain a consistent proportionality to their effects.

But all the major components of global climate - air, water, ice and vegetation - are actually nonlinear: at certain thresholds they switch from one state of organization to another, with catastrophic consequences for species too finely-tuned to the old norms. Until the early 1990s, however, it was generally believed that these major climate transitions took centuries if not millennia to accomplish. Now, thanks to the decoding of subtle signatures in ice cores and sea-bottom sediments, we know that global temperature and ocean circulation can change abruptly - in a decade or even less.

The paradigmatic example is the so-called 'Younger Dryas' event, 12,800 years ago, when an ice dam collapsed, releasing an immense volume of meltwater from the shrinking Laurentian ice-sheet into the Atlantic Ocean via the instantly-created St. Lawrence River. The freshening of the North Atlantic suppressed the northward conveyance of warm water by the Gulf Current and plunged Europe back into a thousand-year ice age.

Abrupt switching mechanisms in the climate system, like relatively small changes in ocean salinity, are augmented by causal loops that act as amplifiers. Perhaps the most famous example is sea-ice albedo: the white, frozen Arctic Ocean reflects heat back into space, thus providing positive feedback to cooling trends; alternatively, shrinking sea-ice increases heat absorption and accelerates its own melting and planetary warming.

Thresholds, switches, amplifiers, chaos - contemporary geophysics assumes that earth history is inherently revolutionary. This is why many prominent researchers - especially those who study topics like ice sheet stability and North Atlantic circulation - have always had qualms with the consensus projections of the Intergovernmental Panel on Climate Change (IPCC), the world authority on global warming. by Mike Davis; October 05, 2005


3.3. Elements of Climate

3.3.1. Meteorological data In Botswana the responsibility for the collection,

processing, storage and dissemination of meteorological data rests with the Department of Meteorological Services (DMS) in the Ministry of Environment, Wildlife and Tourism. The DMS maintains synoptic weather stations at the following locations around Botswana:

o Francistown o Ghanzi o Jwaneng o Kasane o Letlhakane o Mahalapye o Maun o Pandamatenga o Selebi-Phikwe o Sir Seretse Khama Airport o Shakawe o Sua Pan o Tshabong o Tshane

A wide range of variables are measured, including the

following: o Dry Bulb Temperature o Humidity o Wind Speed o Wind Direction o Rainfall

o Sunshine hours o Evaporation o Air pressure o Soil Temperature

In addition, rainfall and temperature are measured at a large

number of other locations by volunteers who regularly submit their data to DMS.

3.3.2. Temperature Air temperature (Dry Bulb temperature) is the characteristic

of climate that most directly affects comfort. It determines the rate of heat transfer by conduction and convection. Assuming that there are no significant sources of radiant heat transfers, DB temperature is the main determinant of human comfort, and therefore the most significant variable to be specified when defining indoor climate requirements. Heating and cooling equipment is generally controlled by thermostats that are set to a particular target temperature or temperature range.

Dry bulb temperatures in Gaborone vary throughout the

year, between an average daily maximum temperature of 32°C in October, and an average daily minimum temperature of 4°C in July. [Bauer Consult].

The maximum daily temperature in summer typically

occurs at about 3.00pm, and the minimum daily temperature in winter typically occurs at 7.30am.

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Fig. 3.2 Temperatures in Gaborone, by month.

Fig. 3.4 Relative Humidity in Gaborone, by month.

Fig. 3.3 Temperatures in Gaborone, by hour.

Fig. 3.5 Relative Humidity in Gaborone, by hour.

RH DATA MONTHLY GABORONE 2000-2002

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TEMP DATA MONTHLY GABORONE 2000-2002

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ASHRAE design temperature Gaborone Airport (Jan) based on 0.4% chance of exceedance (derived using IES software)

37.7 19.9 20%

CIBSE A guide (5th Ed) design temperature Maun (October) 39 22 24% CIBSE A guide (5th Ed) design temperatures Maun (Jan) 37 25 39% CIBSE A guide (5th Ed) design temperatures Ghanzi (Nov) 38 23 29% CIBSE A guide (5th Ed) design temperatures Ghanzi (Jan) 37 24 36% Standard design conditions in common usage (Gaborone) 38 25 36% More extreme design conditions (Gaborone) 40 27 38% Based on the Typical Meterological Year (TMY) for Gaborone and Maun generated by Meteonorm:

Heating Dry Bulb temperature (99% chance of no lower temperature, Gaborone) 2.5 Cooling Dry Bulb temperature (1% chance of higher temperature, Gaborone) 34.1 25.6 61% Heating Dry Bulb temperature (99% chance of no lower temperature, Maun) 6.3 Cooling Dry Bulb temperature (1% chance of higher temperature, Gaborone) 39.1 22.4 45% Table 3.1 Design Day Conditions for Gaborone, Maun, and Ghanzi

3.3.3. Design Day Conditions Although it is recommended that buildings are simulated

using real weather data (see section @@) some buildings may continue to be designed using “design day” methods. Typical design temperatures for both cooling and heating design are provided in Table 3.1 above.

The choice of design day temperatures is something that the

client must sign off, since it involves a choice about how often the building is likely to overheat, versus the risk of oversizing plant. Generally, for an energy efficient building

it is desirable to use lower design temperatures and allow the building to overheat occasionally.

One of the reasons that more extreme design conditions are

used is to give a design margin and effectively to give the client future flexibility for increased heat loads or for variations/defects in the construction of the building post design stage. However, this should be avoided as it is likely to result in over sizing of plant.


3.3.4. Humidity Humidity is a measure of the moisture content of the air. It

is generally measured as relative humidity, which indicates the percentage saturation of the air.

Relative humidity (RH) is an important characteristic of

climate with regard to building design for the following reasons: o It is a determinant of the comfort zone temperatures. o It determines the effectiveness of evaporative

cooling. Generally RH varies inversely with temperature through the

day. It is higher in the summer months when rain occurs than in the dry months of winter.

For Gaborone the highest hourly average RH is 90% and

occursin June. The lowest hourly average RH is 28% and occurs in September. [Bauer Consult]. Maximum RH typically occurs at 7.00am, while minimum RH typically occurs at 5.00pm.

3.3.5. Radiation Radiation is a critically important characteristic of climate,

both at a macro, outdoor level and in relation to indoor climate.

Heat transfer by radiation is proportional to the difference

in temperature of the surfaces raised to the fourth power. It is therefore a minor component of total heat flow between surfaces where the temperature difference is small, and rapidly becomes the major component of heat flow when

temperature difference increases. It is also affected by other characteristics of the surfaces, including colour and texture, as well as the translucence of the intervening space.

During the day radiant heat transfer between a building and

its surroundings is primarily in the form of solar heat gain, and includes direct, diffuse and reflected radiation.

During the night, radiant heat loss to the night sky occurs

from any surface in view of the sky. Total solar radiation received on a horizontal surface has

been recorded at Sebele since 1977. For other locations it has been calculated from recorded measurements of bright sunshine duration using the Angstrom formula.

The annual average daily total radiation on a horizontal surface varies between 19.6 MJ/m2.day in Sebele, to 22.0 MJ/m2.day in Tsabong. [Bhalotra]

The monthly average daily total radiation on a horizontal

surface for Gaborone varies from 14.6 MJ/m2.day in June, to 26.2 MJ/m2.day in December. [Bhalotra]

The indoor radiant environment is often underestimated as

a factor in determining comfort. A space may feel uncomfortably hot even when the air temperature is several degrees below the minimum comfort level, if there is a hot surface in view (such as the sun, seen through a window, or even a warm wall). Likewise, a space with an air temperature higher than the maximum comfort level may feel cold if there is a view to a cold body such as the night sky. (See Section 4, Indoor Environment.)


3.3.6. Wind Wind is significant in energy efficient building design as a

driving force for ventilation, which is of benefit in the following ways: o Natural ventilation to improve air quality. o Natural ventilation to provide cooling air movement. o Wind driven evaporative cooling.

Wind driven infiltration is a problem in the following ways:

o Heat loss through infiltration. o Heat gain through infiltration. o Excessive air speeds due to infiltration in high winds. o Entry of dust or other contaminants due to

infiltration. Wind direction for most of Botswana is predominantly

from the East, with a significant component from the south to southwest in the extreme southwest of the country. There are extensive periods of calm, e.g. 37.7% for Gaborone.

It would be important to analyse wind data to determine

whether there is a difference between the dominant wind direction for light winds and for strong winds.


3.3.7. Rainfall Rainfall has limited direct effect on building energy

performance, but is important since it is closely linked to other climate variables. For example, in a year of good rainfall, the hottest month of the year is frequently October, which in such years is generally still dry with little cloud cover. Rainfall during the months of December and January helps to reduce temperatures through evaporation and reduced sunshine hours. In years of drought, the reverse is the case, with temperatures in December and January exceeding those of October.

Rainfall must be taken into consideration in designing the

landscape around a building. Plants that require much irrigation should be avoided, since water is a scarce resource in Botswana. Opportunities for using greywater should be considered in any building project. The website at www.oasisdesign.net has useful information on practical greywater design solutions.

3.4. Climatic Zones. Botswana extends from latitude 17°,50’ at Kasane in the

north, to latitude 26, 59’ at Bokspits in the south. The western border with Namibia runs along longitude 20, 0’ E, while the confluence of the Limpopo and Shashe rivers in the east is located at longitude 29°, 30’E. The country spans approximately 1,100 km from north to south, and 965km from west to east.

The variations in climate across the country are such that they need to be taken into consideration in building design for comfort and energy efficiency.

Fig. 3.7 shows the monthly mean maximum and minimum

temperatures for various locations around Botswana.

Fig.3.6 Map of Botswana (source: US – CIA)


Fig. 3.7 Temperatures in different locations. (1961-1990)

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Fig. 3.8 Relative Humidity in different locations. (1961-1990)

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There is considerable variation in temperature in different areas of Botswana. Generally winter minimum temperatures are higher the further north you go, with average minimum temperatures in July of 1°C for Tsabong, compared to 11°C in Kasane. Extreme minimum temperatures vary much more, with the coldest monthly mean temperature in Tsabong being –9.5°C compared to 3°C in Kasane.

Maximum summer temperatures show less variation, with

the mean maximum temperature for January of 35.1°C in Tsabong, compared to the mean maximum temperature for October in Kasane of 33.9°C. The highest monthly mean temperature in Kasane was 41.5°C compared to 42.1°C in Tsabong.

In the north of the country there is little or no need for

winter heating, whereas this is required in the south, and particularly southwest.

It is recommended that for building energy purposes the

Ngamiland District and Chobe District which include Maun, Shakawe and Kasane should be regarded as the Northern Climate Zone, and the remainder of the country be regarded as the Southern Climate Zone.

3.5. Climate Patterns. In addition to the geographical variations in climate, there

are also patterns of climate within one locality. In considering the impact of climate on building energy performance, it is important to consider the different patterns that occur, and differentiate these from the average characteristics, which may never actually be experienced.

During the winter there tend to be a succession of cold

fronts that move across southern Africa from the south to the north. These are experienced in Botswana as a period of time, ranging from a few days to about two weeks with low temperatures, cold southerly winds, and clear skies. In low lying areas between hills, these are the times when frost is experienced. Typically these cold spells occur in the month of June, or Seetebosigo (don’t visit at night).

In between these cold fronts, the winter weather may be

relatively warm during the day, when the sun warms the still air, and cool at night with the minimum temperature experienced at dawn when the earth has had a full 9-10 hours of radiation to the clear night sky. The difference may be as much as 8°C in minimum temperature within a week. If the average hourly temperature were to be taken for design purposes, the actual conditions would never be reflected.

In the summer there is perhaps even more variety in

climatic patterns, with some years being generally dry years of drought, some years wet, with ‘good’ rains, and many years falling somewhere in between. During years of good


rain, a daily cycle may occur for several weeks at a time, with clear skies until mid afternoon, when thunderclouds roll in from the southwest, breaking into a violent thunderstorm in the late afternoon. When this has exhausted its load of moisture onto the earth, the clouds simply disappear, leaving a clear sky at or just after sunset, and throughout the night. Following a cycle of such daily storms, there may be a period of dry weather with not a cloud to be seen for days or even weeks at a time. Again, the average data for a month that includes both types of weather pattern would provide a weather picture that may never actually occur in reality.


3.6.1. Books and papers Anderson, R. 1970. ‘Climatic Factors in Botswana’. Botswana Notes

and Records Volume 2 pp. 75-78. The Botswana Society. Bauer Consult. Gaborone climatic data based on hourly data for

years 2000-2002, provided by Department of Meteorological Services.

Bhalotra, Y.P.R. 1987. Climate of Botswana Part II: Elements of

Climate. Department of Meterorological Services. 1. Rainfall. 2. Sunshine and Solar Radiation & Evaporation. 3. Temperatures & Humidity of the Air. 4. Surface Winds & Atmospheric Pressure.

Bhalotra, Y.P.R. 1985. Rainfall maps of Botswana. Department of

Meterorological Services. van Deventer, E.N. 1971. “Climatic and other Design Data for

Evaluating Heating and Cooling Requirements of Buildings” CSIR Research Report 300. Reprinted as CSIR Report Number: BOU/R9704, June 1997.

Green Building Guidelines: Meeting the Demand for Low-energy

Resource-Efficient Homes, 2004. Sustainable Buildings Industry Council.

Hamilton, L.B., et. al. 1984. Passive Solar Design Workbook.

BRET. Botswana.


Lechner, N. 1990. Heating, Cooling, Lighting – Design Methods for

Architects. USA. John Wiley & Sons.

3.6.2. Web resources ASHRAE American Society of Heating, Refrigerating and Air-

conditioning Engineers. http://www.ashrae.org/ CIBSE Chartered Institute for Building Services Engineers http://cibse.org/ Department of Meteorological Services, Botswana Government. http://www.weather.info.bw/ EDR. Energy Design Resources http://www.energydesignresources.com/ EERE Building Technologies Program Home Page http://www.eere.energy.gov/buildings/ Intergovernmental Panel on Climate Change http://www.ipcc.ch/ Oasis Design http://www.oasisdesign.net/ SBIC. Sustainable Buildings Industry Council. http://www.sbicouncil.org/

South African Weather Service http://www.weathersa.co.za/ SQUARE ONE environmental design, software, architecture,

sustainability. http://www.squ1.com/site.html U.S. DOE Energy Efficiency and Renewable Energy (EERE) Home

Page http://www.eere.energy.gov/ WBDG - Whole Building Design Guide http://www.wbdg.org/

SECTION 4 INDOOR ENVIRONMENT


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CONTENTS

4. INDOOR ENVIRONMENT 5

4.1. Overview 5

4.2. Elements of Indoor Environment. 5

4.3. Climatic aspects of the indoor environment. 6 4.3.1. Temperature and humidity. 6 4.3.2. Mean radiant temperature. 6 4.3.3. Air velocity. 7

4.4. Non-climatic aspects of the indoor environment. 7 4.4.1. Air quality. 7 4.4.2. The aesthetic environment. 8 4.4.3. Lighting levels and daylighting. 9 4.4.4. Static electricity 9 4.4.5. Ionising radiation 9

4.5. Human comfort. 9 4.5.1. Mechanisms of heat exchange. 10 4.5.2. Evaporation. 10 4.5.3. Convection. 11 4.5.4. Radiation. 11 4.5.5. Conduction. 11

4.6. Factors affecting human comfort. 12 4.6.1. Clothing. 12 4.6.2. Activity. 13 4.6.3. The comfort zone - the psychometric chart. 13

Energy Efficiency Building Design Guidelines for Botswana – Section 4. Indoor Environment

4.7. Specification of the indoor thermal environment. 14 4.7.1. ASHRAE Standard 55-2004. 15 4.7.2. Adaptive comfort. 17 4.7.3. Adaptive comfort in conditioned buildings. 19 4.7.4. Adaptive comfort applied to Botswana climate. 19

4.8. Resource material 21 4.8.1. Books and papers 21 4.8.2. Codes and Standards. 21 4.8.3. Websites. 21

Energy Efficiency Building Design Guidelines for Botswana – Section 4. Indoor Environment Page 5

4. INDOOR ENVIRONMENT

4.1. Overview This Section addresses the subject of indoor environment

and its impact on building energy performance in Botswana. The topics that will be covered are briefly outlined below.

A building may be defined as:

A structure that provides spaces having an environment that is

amended from that of its surroundings to suit particular

purposes. The definition of the indoor environment that will be

suitable for a particular purpose is therefore very important, as this is a key component of the specification for the building.

Indoor environment has a strong relation to energy

performance in most buildings, since a large proportion of the building’s energy consumption is used to amend the indoor environment particularly the climate and lighting.

The paper will consider the elements that make up the

indoor environment, which include both climatic and non-climatic aspects.

Human comfort is often the main requirement of the indoor

environment. The processes that the body uses to achieve

climatic comfort will be discussed, as well as the factors that affect this.

Standards are available that attempt to define indoor

conditions that will be experienced as ‘comfortable’. These are briefly considered, as well as some recent developments in our understanding of how to define standards for comfort, particularly with regard to improving energy efficiency in buildings.

4.2. Elements of Indoor Environment. The concept ‘indoor environment’ includes all aspects of

the relationship between the occupants and contents of a building and their surroundings within the building. This may be considered in terms of climatic and non-climatic aspects, which are defined by the following principle parameters:

Climatic:

o Dry Bulb temperature. o Relative Humidity. o Mean radiant temperature. o Air velocity.

Other parameters:

o Air quality. o Aesthetic environment including

Spatial geometry Colour. Views.

o Lighting levels and daylighting.


o Acoustic environment. o Vibration. o Static electricity o Ionizing radiation o Occupancy density

These are discussed in more detail in the following

sections, with emphasis on parameters relating to energy consumption.

4.3. Climatic aspects of the indoor environment.

4.3.1. Temperature and humidity. Temperature and humidity are the most important aspects

of the indoor climate. They largely determine human comfort; due to the impact they have on several of the body’s heat transfer mechanisms (see below).

Storage of sensitive materials such as books, paper, food,

medicines etc. and specifications for machines and equipment may dictate particular requirements for temperature and relative humidity other than for human comfort.

Relative humidity needs to be controlled both for comfort,

but also to prevent algae, moulds, fungi etc from forming. Condensation at cold surfaces can also cause problems if humidity is too high. Part of the ventilation requirement comes from the fact that humans emit humidity into the air.

4.3.2. Mean radiant temperature. The radiant environment may be as important a criterion

for comfort as temperature and humidity. The extent of radiant heat transfer between the body and the environment is mainly dependant on the following:

Geometric arrangement of the radiating surfaces. Surface characteristics of opaque surfaces (wall, ceiling,

floor): o Surface colour and texture (emissivity). o Surface temperature.

Characteristics of translucent surfaces (window):

o Transmissivity o Temperature / surface characteristics of bodies

beyond the translucent surface (e.g. sun or night sky) Human body:

o Surface area exposed o Colour / texture of clothing.

Radiant heat transfer will be particularly significant in

spaces in which people are exposed to large surfaces that are at a temperature that is different from the ambient temperature. This may be the case in buildings with large areas of glazing. If these are orientated to admit direct sun, this can be a source of heat gain. Thermal mass walls, floors and ceilings may be used for radiant cooling if the surface temperature is lower than ambient. However it is generally recommended (e.g. by the Danish Building Institute) not to have a ΔT > 5-10° C to avoid


compromising human comfort in locations with stationary workplaces.

The radiant environment at any particular location is

defined by the Mean Radiant Temperature, which is defined as:

“the uniform surface temperature of a black enclosure

with which an individual exchanges the same heat by radiation as the actual environment considered”.

The weighted average of the Mean Radiant Temperature

and the Dry Bulb temperature is termed the ‘Operative Temperature’ and is the temperature that is generally used in standards for human comfort (e.g. the ASHRAE Standard 55-2004). Buildings with heavyweight ceilings and floors tend to have a lower Mean Radiant Temperature than those with lightweight partitioning elements due to the thermal capacity of these elements. As a result they have a lower Operative Temperature in the summer, even when the air temperature is the same resulting in a more comfortable indoor environment.

4.3.3. Air velocity. Air movement affects both convection and evaporation,

which are important methods of heat loss from the body. The comfort temperature is highly dependant on air velocity, particularly if light clothing is worn. Control of air movement with fans is an important opportunity to give individuals control over their climatic environment. Using air movement to control comfort is a delicate balance since too high an air velocity (or too large a temperature

difference) will generally cause discomfort due to draught (typically at air velocities > 0.2 m/s – especially if the air temperature is significantly different from the comfort temperature (most people will have experienced discomfort from e.g. sitting in the cold air stream of an air conditioner, or the relief a fan can provide in an otherwise stifling heat).

4.4. Non-climatic aspects of the indoor environment.

4.4.1. Air quality. Air quality is an important aspect of the indoor

environment that is often neglected in naturally ventilated buildings. It may also conflict with other strategies for energy efficiency.

Reduction of infiltration is an important strategy to reduce

energy consumption. This however has the effect of reducing natural ventilation, which allows the build up of indoor air contaminants.

Indoor air quality is determined by many factors, including:

o Equipment and appliances used in the building. o Occupant activity (e.g. smoking). o Building materials. o Outdoor air quality.

Typical contaminants that affect air quality include gasses,

particularly Carbon Dioxide, vapours and odours, fungi, moulds, dust particles that may be biological or mineral in origin.


Indoor air quality may be controlled by adopting standards for ventilation such as ASHRAE Standard 62-1989 or the proposed CEN standard “Ventilation for Buildings. Design Criteria for the indoor environment.” CEN/CR 1752: 1998-12; CEN; Bruxelles 1998.

The ASHRAE standard is currently under revision, and sets

requirements for outdoor air ventilation for different purposes (typically 2.5l/s per person for office spaces).

Danish guidelines recommend at least 7 l/s per person in

offices (4 l/s per person is the minimum), where smoking is not permitted. If smoking is permitted 10 l/s pr person is the minimum and 20 l/s pr. person is recommended. Danish Building regulations require a minimum 0.5 ACH (air changes per hour).

Alternatively performance criteria may be adopted,

specifying target concentrations of contaminants. An example of such criteria is the National Ambient Air

Quality Standards that are defined by the EPA as a requirement of the Clean Air Act (USA). Such standards are difficult to implement, due to the problem of measuring a large number of different potential contaminants.

4.4.2. The aesthetic environment. The aesthetic environment is an important aspect of the

indoor environment. The geometry of the spaces in the building affects how

people respond to the rooms. High ceilings create a feeling

of spaciousness, but can also be intimidating, whereas low ceilings can make a room feel more intimate. Spatial geometry also affects the air temperature and air movement in a room. High ceilings can allow stratification of air, so that the warmer air rises above the inhabited zone, which will be cooler.

Colour is a very important aspect of the indoor

environment. People respond to colours with their emotions and feelings, and colour can be used to change the perception of space, e.g. a dark colour on the ceiling makes it appear lower. Colours also impact on illumination contrasts which if too high may cause discomfort. Colour is an integral aspect of lighting design; light colours reflect light, and can reduce the number and power of light sources required to achieve a particular lighting level. White ceilings combined with light shelves can allow daylight to penetrate deeper into a building.

Views from windows change the way people respond to

indoor environments. The opportunity to see outdoors can make people feel less enclosed, which can affect their work performance positively. Views to green areas, vegetation and water are generally considered to positively affect the perceived comfort of indoor environments. Excessive distraction can also reduce performance, especially in classrooms, where views may need to be limited to avoid this.


4.4.3. Lighting levels and daylighting. The light characteristics of the indoor environment have a

major impact on almost all activities that take place there, and also on the energy performance of the building.

The details of what these characteristics should be, and how

they may be achieved in an energy efficient manner are discussed in detail in Section 9, Lighting, Artificial and Daylighting.

Specifications of lighting levels required for different tasks

have been defined in various standards, codes and guidelines. Recent research has focussed on the impact of the quality of lighting as well as the quantity. For many years the importance of factors such as colour response of different light sources have been studied.

Many studies have been conducted on the impact of

lighting levels on behaviour, including productivity, retail sales, absenteeism, etc. These have demonstrated a strong correlation between behaviour and lighting levels including for example, significant increases in retail sales with higher light levels.

4.4.4. Static electricity Static electricity tends to be an important criterion for

comfort in environments with low air humidity; frequently the case in Botswana. It is more serious where insulating floor finishes are used, and is a particular problem in environments in which sensitive electronic equipment is used, manufactured or repaired.

It is not especially relevant in relation to energy efficiency.

4.4.5. Ionising radiation Increasing concern is being focussed on sources of ionising

radiation, as for example from leakage of the gas Radon from the ground. This is a very localised phenomenon that appears not to have been sufficiently researched in Botswana to determine the extent to which it may be a problem.

4.5. Human comfort. Human comfort is related to the individual’s perception of

the quality of the environment in which he or she is situated. People experience the environment differently, so that one person may feel uncomfortably hot and another too cold in the same place. Designing for human comfort is therefore always a compromise, the aim being to provide an indoor climate that is experienced as adequately comfortable by a large majority of people. A common unit for the measurement of human comfort is the PMV. This is the ‘predicted mean vote’, and indicates the percentage of people who are predicted to feel comfortable in any given set of conditions. In practice it is generally difficult to get acceptance ratings much over 80-90%, which are therefore generally used as normal design values.

The physiology of human beings as warm-blooded

mammals requires the internal body temperature to be maintained within very close limits (between 36°C and 38°C, the normal temperature being 37°C). If it falls below 30°C or rises above 41°C, death is imminent. Considering that humans live in environments where the external


temperature varies between -40°C to over 50°C, this is quite a demanding requirement. The body has a number of mechanisms that it uses to achieve this. Heat is released into the body by all metabolical processes, including eating, respiration, movement, etc. In order to maintain a balanced temperature, the body must therefore find ways to lose heat at the same rate at which it is being produced by these processes.

4.5.1. Mechanisms of heat exchange. There are essentially four basic mechanisms by which the

body exchanges heat with its environment. o Evaporation. o Convection. o Radiation. o Conduction.

Evaporation and convection are mechanisms of heat loss

for the body. Radiation and conduction can result in either heat gain or heat loss depending on the temperature of body relative to its surroundings.

4.5.2. Evaporation. Evaporation takes place during respiration, whereby fluid

from the body enters the air that we breath in the lungs and the respiratory duct and is evaporated, absorbing the latent heat of evaporation from the surfaces of these organs.

Evaporation also takes place at the skin as a result of

perspiration.

The rate of heat transfer by evaporation is determined by the rate at which moisture can be removed by the air. This in turn is dependant on both the capacity of the air to absorb moisture, and the rate of movement of the air. The capacity of the air to absorb moisture is dependant on its relative humidity, which is a function of temperature and absolute moisture content.


Fig 4.1 Heat exchange between the human body and its

surroundings.

4.5.3. Convection. Convective heat transfer occurs where the skin is in contact

with a fluid at a different temperature, such as air. The rate of heat transfer by convection is determined by the

difference in temperature, and the flow rate of the fluid (air speed), as well as the geometry of the surface-flow interface (e.g. the exposed surface area).

4.5.4. Radiation. Radiant heat transfer takes place between any two bodies

that are in sight of each other and at different temperatures. The rate of heat transfer by radiation is determined by the

relative areas of the two surfaces, their surface temperatures and their emmittance / absorbtance properties at the respective wavelengths relating to these temperatures.

4.5.5. Conduction. Heat transfer by conduction occurs where the skin is in

direct contact with another surface, such as the floor, and there is a difference in temperature between the surfaces.

The rate of heat transfer by conduction is determined by the

conductivity of the two surfaces, their heat capacity and the difference in temperatures.


4.6. Factors affecting human comfort.

4.6.1. Clothing. All the four mechanisms of heat transfer are greatly

influenced by clothing. This can provide insulation to reduce mainly convective and radiant heat transfer (but also conductive – e.g. wearing gloves and protective clothing when hot or very cold surfaces/objects are handled. Shoes reduce heat loss/gain from the floor). Clothing can prevent air movement at the skin, which almost eliminates convective and evaporative heat transfer from the skin. The effect of clothing on evaporative heat transfer is dependant on the type of material. Some materials, such as cotton and wool allow moisture to pass through, and therefore do not inhibit evaporative heat loss as much as non-porous materials. Clothing can also reduce radiant heat transfer, as the thermal resistance of the clothing will reduce the flow of heat from the body.

By selecting appropriate clothing for a particular climate

and activity, the range of indoor climate that is experienced as comfortable can be considerably extended, both to lower temperatures, if insulating clothing is worn, or to higher temperatures with clothing that allows free flow of air to a larger area of the body.

Cultural aspects can have an important influence on what is

acceptable attire for particular activities. Recently the Japanese government has introduced a policy called ‘Cool Biz’ to discourage the wearing of jackets and ties in the

summer, as a way to reduce energy consumption in office buildings.

A measure of the thermal resistance of clothing has been

developed, called the ‘clo-value’. This is a measure of the ratio of thermal resistance of clothing to a standard value of 0.155m2K/W, which is typical of a business suit.

Typical clo values are as given in Table 4.1

Clo – value Example 0 Naked, swimwear 0.5 Light trousers + shirt, light dress +

blouse 1.0 Business suit, dress + jumper 2.0 Heavy suit, overcoat, gloves and hat

Table 4. 1.Typical clo-values. Source:

www.esru.strath.ac.uk/Courseware/Class-16293/6-Comfort.pdf


4.6.2. Activity. As stated earlier, the body is continuously producing heat

as a result of metabolic processes. The rate of heat production varies greatly depending on the activity that one is engaged in. Typical rates of heat output are presented in Table 4.2.

Activity Heat output

(male): WattsHeat output

(female): WattsSleeping 70 60Seated 115 98Light work 150 128Medium work 265 225Heavy work 440 374

Table 4.2. Heat output for different activities.

4.6.3. The comfort zone - the psychometric chart. Human comfort in the indoor environment is related to the

interaction of a large number of variables in addition to temperature.

These can be illustrated by means of a psychometric chart,

which shows the interaction of temperature and humidity. The combination of these parameters that is experienced as comfortable can be shown for different levels of clothing and air speed. This is illustrated in Fig. 4.2.

Fig 4.2 Psychometric chart (source: The Psych Tool,

Square One Research Ltd.).


4.7. Specification of the indoor thermal environment.

The specification of the indoor climate is an important component of an effective design brief for any building, particularly in relation to energy performance. The preceding discussion on the impact of climate on performance shows how comfort is influenced by factors such as activity and clothing. Other factors also influence comfort, including expectations based on recent weather. There is also considerable variation between individuals in their perception of comfort. As a result it is impossible to satisfy all the occupants of an indoor space.

Many studies have been conducted to determine the

conditions for human comfort. These included surveys of large numbers of people who were asked to indicate their level of comfort on a scale from say, -3 (cold) to +3 (hot). This is known as the PMV scale (Predicted Mean Vote).

Tests were carried out on large groups of individuals by

Fanger in Denmark and by others in many other countries. Fanger concluded that: o there is no significant difference in comfort

perceptions due to geographical location or season (including tropical regions);

o there is no significant difference due to age (e.g. because older people have lower metabolic rate counteracted by lower perspiration rates);

o there is no significant difference due to sex; o there is no significant difference due to body build;

o there is no significant difference due to ethnic origin. Based on these studies, empirical formulae have been

prepared that predict the degree of comfort that will be reported by a certain proportion of occupants under particular conditions.


4.7.1. ASHRAE Standard 55-2004. The most commonly accepted standard specifying the

thermal indoor environment for comfort is the ASHRAE Standard 55-2004 - Thermal Environmental Conditions for Human Occupancy (ANSI Approved). This is similar to the CIBSE Standard 55-1992 - Thermal Environmental Conditions. This standard specifies the combinations of indoor space environment and personal factors that will produce thermal environmental conditions acceptable to 80% or more of the occupants within a space. The environmental factors addressed are temperature, thermal radiation, humidity, and air speed; the personal factors are those of activity and clothing.

The ASHRAE standard has an upper limit for humidity

ratio of 0.012. This translates approximately to a relative humidity of 75% at a dry bulb temperature of 21°C and 53% at 27°C. In Botswana RH is often above the minimum level, particularly in the mornings in summer.

There is some doubt as to whether this requirement is fully

justified. The characteristic that is defined is humidity ratio, whereas it may be more appropriate to define relative humidity. It may also be that the boundary is lower than necessary in terms of people’s perception of comfort.

The specification to be adopted for maximum humidity has

a big impact in determining the conditions under which evaporative cooling is effective. An unnecessarily low ceiling for humidity would therefore restrict the use of

evaporative cooling in situations where it may in fact be effective.


Fig 4.3 Simplified graphs indicating winter and summer comfort zones based on ASHREA 55-2004 (Source: Energy Plus Reference Manual)


4.7.2. Adaptive comfort. The standard acknowledges the concept of adaptive comfort. It has been found that people experience thermal comfort quite differently in buildings that are naturally ventilated without mechanical cooling than in buildings that are mechanically cooled. The standard specifies a far more relaxed set of comfort conditions for such buildings, with the requirement that people should have the opportunity to open and close windows, and freedom to adapt their clothing to achieve comfort. The comfort zone is then related to mean outdoor air temperature, and for typical January conditions in Gaborone (To=25°C) would be between 22-29°C. The acceptable temperature range for air-conditioned buildings in the same situation is between 25-28°C for light clothing (0.5clo) or 19-25°C with more formal clothing (1.0clo).

The specification for air-conditioned buildings also requires

that the variation in temperature during any 15min period is no more that 1.1°C. This typically determines the cycling band for the control system. No such requirement is made for the adaptive comfort specification, since it is assumed that people will respond to any variations within the comfort zone by making adjustments to their clothing, or ventilation.


Fig. 4.4 Adaptive comfort temperatures (Source: ASHRAE Standard 55-2004)


4.7.3. Adaptive comfort in conditioned buildings. It appears that there is considerable scope for energy

savings if the concepts of adaptive comfort could also be applied to conditioned buildings. This would require an approach that allowed some user adaptation within the overall framework of a controlled mechanically conditioned building. A simple example of such an approach would be the use of individually controlled fans and radiant heaters to allow individuals more control of their immediate surroundings. Encouraging the use of thermally appropriate clothing would further relax the demands on the mechanical equipment.

Research summarised by Nicol, J.F. and Humphreys, M.A.

in their paper “Adaptive thermal comfort and sustainable thermal standards for buildings.” [3] suggests that the monthly mean temperature may not be the most appropriate for determining the comfort zone in an adaptive comfort model, and suggest that a method that accounts for the temperature variation of the previous few days would provide a more accurate model. An algorithm for determining this is proposed, which could also be used control temperature in conditioned buildings, resulting in substantial energy savings.

4.7.4. Adaptive comfort applied to Botswana climate. The relationship between indoor comfort temperature and

outdoor mean temperature has been consistently found to be close to:

Tc = 13.5 + 0.54To

Where Tc = Thermal comfort temperature To = Monthly mean outdoor temperature When this is applied to the temperature data for Gaborone,

the thermal comfort temperature is as shown in Fig.4.5. This indicates that at all times of the year the comfort

temperature is above the mean monthly temperature. This suggests that for buildings for which the envelope loads dominate, thermal comfort should be achievable with no mechanical equipment, although other aspects of indoor environment may still require this, e.g. mechanical ventilation to achieve air quality standards. Even buildings with more substantial internal loads could be comfortable with minimal energy use if this is acknowledged as an important design criterion, and the knowledge and tools to achieve it are available.


COMFORT TEMPERATURE GABORONE 2000-2002(based on Tc=13.5+0.54To)

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Fig. 4.5 Comfort temperature for Gaborone.


4.8. Resource material

4.8.1. Books and papers Energy Plus. “Input Output Reference - The Encyclopedic

Reference to EnergyPlus Input and Output” December 2005.

Green Building Guidelines: Meeting the Demand for Low-energy

Resource-Efficient Homes, 2004. Sustainable Buildings Industry Council.


BRET. Botswana. Hunn, B.D. (ed) 1996. “Fundamentals of Building Energy

Dynamics.” Massachusetts Institute of Technology. Koch-Nielsen, H. 2002 Stay Cool - A design Guide for the Built

Environment in Hot Climates. London: James & James (Science Publishers) Ltd.


Architects. USA. John Wiley & Sons. Nicol, J.F. and Humphreys, M.A. “Adaptive thermal comfort and

sustainable thermal standards for buildings.” Oxford Centre for Sustainable Development, School of Architecture, Oxford Brookes University.

Plympton, P. et. al. “Daylighting in Schools: Improving Student

Performance and Health at a Price Schools Can Afford.”

Conference Paper. Presented at the American Solar Energy Society Conference Madison, Wisconsin June 16, 2000

Tutt, P. and Adler, D. (Ed.). 1979. New Metric Handbook –

Planning and Design Data. Oxford: Butterworth-Heinemann Ltd.

University of Strathclyde. Unit 6 Thermal Comfort. Course 16293: “Environmental Engineering Science 1.” Course material for Energy Systems Research Unit, (ESRU), University of Strathclyde.

4.8.2. Codes and Standards. ASHRAE Standard 55-2004. Thermal Environmental Conditions for

Human Occupancy ASHRAE Standard 62.2-2004 – Ventilation and Acceptable Indoor

Air Quality in Low-Rise Residential Buildings (ANSI Approved)

CEN Standard: “Ventilation for Buildings. Design Criteria for the

indoor environment. CEN/CR 1752: 1998-12; CEN; Bruxelles 1998

4.8.3. Websites. ASHRAE American Society of Heating, Refrigerating and Air-

conditioning Engineers. http://www.ashrae.org/ CIBSE Chartered Institute for Building Services Engineers http://cibse.org/


EERE Building Technologies Program Home Page http://www.eere.energy.gov/buildings/ EDR. Energy Design Resources http://www.energydesignresources.com/ SBIC. Sustainable Buildings Industry Council. http://www.sbicouncil.org/

SQUARE ONE environmental design, software, architecture, sustainability. http://www.squ1.com/site.html WBDG - Whole Building Design Guide http://www.wbdg.org/

SECTION 5 DESIGN & CONSTRUCTION PROCESS ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES FOR BOTSWANA Revision 1 September 2007

Energy Efficiency Building Design Guidelines for Botswana – Section 5. Design and Construction Process Page 3

CONTENTS

5. DESIGN & CONSTRUCTION PROCESS 5

5. DESIGN & CONSTRUCTION PROCESS 5

5.1. Overview 5 5.1.1. Project cost and energy efficiency 5 5.1.2. Procurement systems 5 5.1.3. Integrated Design Methods. 5 5.1.4. Construction and Commissioning. 5

5.2. Project Cost and Energy Efficiency 5

5.3. Procurement Systems. 7 5.3.1. Conventional appointment of consultants. 7 5.3.2. Competitive tendering. 8 5.3.3. Turnkey development. 8 5.3.4. Public, Private Partnership. 9 5.3.5. Fee incentives for energy efficiency. 9

5.4. Integrated Design Methods. 12 5.4.1. Integrated design coordinator. 13 5.4.2. Structured methodology. 13 5.4.3. Incentives. 14 5.4.4. Timing of design decisions. 15 5.4.5. Construction. 16

5.5. Commissioning. 16

5.6. Resource Material 17

Energy Efficiency Building Design Guidelines for Botswana – Section 5. Design and Construction Process

5.6.1. Books and Papers 17 5.6.2. Web resources 17

Energy Efficiency Building Design Guidelines - Section 5. Design and Construction Process Page 5

5. DESIGN & CONSTRUCTION PROCESS

5.1. Overview This section addresses the subject of the design and

construction process and its impact on building energy performance in Botswana.

The following topics are covered in this section:

o Project cost and energy efficiency. o Procurement systems and their implications for

energy performance. o Integrated design methods. o Construction and Commissioning.

5.1.1. Project cost and energy efficiency The relationship that exists between project cost (capital

and recurrent) and energy efficiency is described.

5.1.2. Procurement systems The process and methodology by which the design,

construction, operation and demolition of buildings is implemented has gone through dramatic changes over past 30 years in many countries of the world. A number of different approaches to procurement of design services are now implemented, including competitive tendering, turnkey development and Public / Private Partnership. The implications of these approaches with regard to improving energy efficiency are considered, as well as the relationship between initial cost, life-cycle cost and energy efficiency.

5.1.3. Integrated Design Methods. Substantial improvements in energy efficiency have been

achieved through the development and implementation of what is known as ‘integrated design’. This is essentially a holistic approach to the design, construction, operation and demolition of a building.

5.1.4. Construction and Commissioning. The effort that has gone into achieving an energy efficient

building design can easily be compromised in the construction process if adequate supervision and coordination is not provided to ensure that the critical aspects of the building meet the design requirements.

The systematic application of commissioning to both new

and existing buildings has been found to be a highly cost effective means to ensure that the building and all its systems are functioning as intended. It can lead to dramatic improvements in energy efficiency, and overall environmental performance.

5.2. Project Cost and Energy Efficiency Over the past two or three decades there has been an

increasing concern for energy efficiency generally, including in the building sector. This has been driven by the increasing cost of conventional sources of energy, as reserves of fossil fuel are becoming more scarce, as well as the impact of our rapidly increasing energy consumption on the local and global environment in the form of pollution and climate change.


This has resulted in a change in the way in which building costs are viewed and assessed. Previously the main concern was with the initial construction cost of a building, and in many cases this is still the only cost that is taken into consideration in the design stages of a building project. The project manager is asked to prepare project budgets, and decisions are based largely on an assessment of whether the client can afford particular features or finishes in the building.

There is a growing awareness that the initial construction

cost is only one aspect of the overall building cost, and that future costs of operation, maintenance and ultimately demolition may be as important or even more so over the total life of the building. There are many choices of material, design, equipment or finishes that influence ‘life-cycle’ cost in different ways. Some choices may lead to reduced life-cycle cost and save on the construction cost as well. Others may reduce life-cycle costs and have no influence on construction cost, and many interventions may require a trade-off between increased construction cost resulting in reduced life-cycle cost.

Life cycle cost is defined more fully in Section 12, Life-

Cycle Cost Analysis. This also gives a brief introduction to various methods of calculating LCC, as well as references to more detailed information.


5.3. Procurement Systems. When a client needs a construction project to be

implemented, the first requirement is usually for some professional advice to assist with preparing the design brief and getting started on the process of design and construction.

The conventional approach to this has often been to employ

a project manager who becomes the client’s agent and manages the project. The project manager then engages an architect to lead the design phase of the project. In many cases the client may employ an architect directly, who then also takes on the functions of project manager.

Until recently this was also the most common approach

taken by the Botswana Government. Recently however a number of other procurement options have been tried, including: o Competitive tendering for consultancy services. o Turnkey development. o Public, Private Partnership (PPP).

These different procurement methods have considerable

implications on the financial and other motivations that influence the work of the consultants. These are discussed in the following sections with particular reference to energy efficiency and energy conservation.

5.3.1. Conventional appointment of consultants. In this case the choice of consultant is based on their

reputation for capability, professional integrity, and

capacity to carry out the work for a reasonable fee. Fees may be negotiated, but are usually based on agreed standard rates that are set by professional institutes. The initial stages of a project may be paid on an hourly or lump sum basis, but the major portion of fees is generally calculated as a percentage of the contract sum related to that consultant’s scope of work. The consultant therefore does not have a financial incentive to reduce contract cost. He or she does have an incentive to reduce the work required of them in completing the project.

Such a consultant has no particular motivation to reduce

life-cycle cost, except in so far as this is included as a concern in the design brief. Some may also see it as a fundamental objective in their work, and seek to achieve this as a matter of course.

Choices that reduce construction cost will result in reduced

fees, and those that increase construction cost will lead to increased fees.

The arrangement is based on an assumption of professional

integrity, which should ensure that these financial motivations do not affect the consultant’s work in any way. This is to some extent reinforced by the codes of conduct that Professional Institutions require their members to adhere to. In practice it is perhaps rather naïve to assume that all consultants have the integrity to totally disregard the financial implications to themselves of decisions that are made in the design and project management process.


5.3.2. Competitive tendering. Recently the Botswana Government changed the standard

method of procurement for consultants to a competitive tendering process. A ‘terms of reference’ (ToR) is prepared and advertised. Consultants prepare tenders that are submitted through the Public Procurement and Asset Disposal Board. Typically the ‘two envelope’ system is used, whereby the technical and financial proposals are submitted in separate envelopes. The technical proposals are first evaluated against a set of criteria. The financial proposals of those tenders that score higher than a certain minimum on the technical evaluation are then opened, and the best value tender is selected.

Generally competitive tendering has resulted in greatly

reduced fees compared to the use of standard fee scales. This is a benefit to the client in that it reduces the portion of project budgets that is spent on fees. It also means that consultants are required to carry out the same amount of work for a lower fee. They are therefore under considerable pressure to minimise their costs in terms of hours spent and the cost of their professional staff (which is generally related to the level of qualification and experience). This may make them reluctant to spend additional time investigating the life-cycle cost implications of different strategies to reduce operating costs generally and energy consumption in particular.

The consultant’s terms of reference (or design brief)

therefore becomes an even more important document and it is essential that environmental considerations and energy performance requirements in particular are clearly defined.

There is also now more of a need to verify that the consultant is actually addressing the requirements of the ToR. On large projects it may be advisable to hire an independent consultant to confirm this. The commissioning procedure (see below) can also help to verify performance against targets, but at that stage it may be too late to correct fundamental design issues.

If the tender is based on percentage rates, then the financial

motivation regarding changes in construction cost versus life-cycle cost will be similar to those for the directly appointed consultant.

If the tender is based on a lump sum fee, then there will be

neither a fee incentive to increase the construction cost, nor a fee penalty if it is reduced.

5.3.3. Turnkey development. The turnkey procurement method is a radical departure

from the traditional relationship between client, consultant and contractor. The design consultants now become part of the same team as the contractor, and tender for a project as a joint venture. The division of the payment between contractor and consultant is decided between them and does not concern the client.

The challenge in this system is to ensure that the client’s

requirements in terms of function, performance and quality are achieved. For larger projects this will often require the client to hire an independent consultant to supervise the project and provide expert advice throughout.


With this system the interests of the contractor and the design consultants are aligned, and they have a financial motivation to reduce costs once a contract has been signed, in order to maximise their profit. This could result in decisions that result in increased life-cycle costs to achieve reduced construction cost, since the turnkey developer has no further involvement in the project once the contract is completed.

As with the competitive tender procedure, it becomes more

important to have a watertight design brief, and a means to verify compliance with the brief.

5.3.4. Public, Private Partnership. Public, private partnership is a relatively new concept in

procurement that is rapidly gaining popularity for medium to large-scale public infrastructure projects, including public buildings. Essentially it takes the turnkey concept further, such that the contractor’s team (the concessionaire) not only designs and builds the project, but also arranges finance, and manages the project for its entire life (or at least a substantial portion thereof). The client in this case pays for the project through ‘unitary’ payments that include for maintenance, building staff, rental, finance, etc. These are calculated as annual payments but are usually paid in monthly instalments rather like a lease charge.

Utility costs such as electricity and water are treated as

‘through costs’ that are paid by the concessionaire and then charged to the client, with an agreed mark-up for profit.

The concessionaire therefore has no direct incentive to design and operate the building in such a way as to minimise energy or water use, since the client covers the cost of these.

The Request for Proposals (RFP) may however include

requirements relating to environmental considerations, energy efficiency, and life cycle costing. The extent to which each proposal addresses these will then be considered in the evaluation of the proposals, and will be one of many criteria used for selecting the successful proposal.

The PPP process includes a procedure to verify that the

completed project meets the targets and requirements of the RFP. This is implemented by the concessionaire under the supervision of a client’s representative, and stringent penalties are charged for any failures to comply. At this stage however it is of course too late to rectify any fundamental design faults.

5.3.5. Fee incentives for energy efficiency. In some countries including the USA a system of fee

incentives and penalties has been introduced for certain projects, to provide a direct financial incentive to consultants to achieve energy efficiency and other objectives. In this case a certain portion of the fees is retained by the client until the initial commissioning process has been completed, during which the performance of the building is monitored. If it is found that the building achieves or exceeds the performance targets, the consultants are rewarded with a bonus. If performance falls


short of the targets, the consultants are penalised. In some cases there may even be ongoing rewards for achieving operation and maintenance cost targets.

An example of a performance based design contract is

provided on the following page.


5.4. Integrated Design Methods. There are substantial opportunities for improving the

environmental performance of buildings through what has become known as ‘integrated building design’ (sometimes also known as ‘integrated energy design’).

The concept requires a re-thinking of the approach to

building design from the one that is traditionally used. Traditionally there has been a tendency to separate out

different systems of a building, with each consultant solving the problems that relate to their expertise in relative isolation. Of course from time to time they come together to look at the implications of each other’s work on the building as a whole, and to coordinate the ‘points of contact’.

Usually the design process begins with the architect who

develops an overall design concept, including the aesthetic and spatial layouts for the building.

A structural engineer takes the concept, ensures that it is

structurally feasible, and works out the structural system that can support it.

A mechanical and electrical engineers then design the

HVAC, lighting and other services systems, trying to fit these into the building as efficiently as possible.

If one is included in the team, then the landscape architect

will be required to create a suitable surrounding for the building.

The integrated design approach, in contrast, views the

building and its surroundings as a whole, comprised of all the different systems interacting with each other to achieve the optimum performance in every respect. There is a deliberate process of looking for opportunities that can arise from these interactions to achieve improved energy efficiency, comfort, quality, beauty, etc.

A number of tools have been developed that can help to

achieve a successful integrated design process, some of which are briefly described below.

INTEGRATED BUILDING DESIGN

The complete building design concept integrates the different system design concepts. o Landscape / environmental design concept. o Architectural design concept. o Thermal design concept. o Structural design concept. o Mechanical and Electrical design concept.


5.4.1. Integrated design coordinator. From the beginning of the project, a specialised energy

consultant is appointed by the client to act as integrated design coordinator. This person is responsible for ensuring that the different members of the design team take into consideration the opportunities that arise in the work of other members, and facilitates the creative interaction between them.

He or she is responsible for assessing the life cycle cost

implications of different alternative approaches that may be suggested by the team, and coordinates the process of selecting the most appropriate combination of design decisions.

5.4.2. Structured methodology. The integrated design approach requires a greater amount

of interaction between the consultants, and a more creative and less formal relationship in the stages where the different design concepts are integrated. However, because much of the design work is carried out concurrently, it is essential that the interaction is facilitated by effective structures for the technical communication.

Details regarding CAD draughting protocols such as layer

names and colours, pensize tables, drawing file names, revision numbering, etc. can make an important difference to the effectiveness of communication between consultants.

Communication channels and media should be agreed on at the beginning, with the integrated design consultant acting as the link between other consultants, to ensure that each has the information that they need at each stage.

Communication with the client, contractor and users must

also be effectively managed, so that they are included in decisions where appropriate, have the information that they need, but are not overloaded with unnecessary information.

Key requirements for integrated building design to be successful:

o The client is convinced of the benefits of this approach and is willing to invest time and money to achieve these.

o Energy efficiency is included as an important

objective in the design brief. o The work of the design consultants is coordinated

towards achieving the agreed objectives. o The construction process is monitored and

managed effectively. o The end users and building operators are trained

in the operation and maintenance of the building.


5.4.3. Incentives. As can be expected, the integrated design process is not

easy, and cannot be achieved without some cost. It will not therefore be generally adopted by choice by consultants unless there is a clear incentive to do so. Much of the potential benefit is only enjoyed by the building owner and / or users during the building’s life time, in the form of reduced energy and other operating costs, better comfort, and a higher quality environment generally. The improvement in these areas can be quite dramatic, with up to 60-70% reduction in energy cost being achieved in certain projects compared to similar, conventionally designed buildings. There is therefore a need to develop an incentive package to compensate the design team for the additional work that is required. This can be done in two distinct ways. One option is to simply pay increased fees up front for the increased service. The alternative is to link the fee to the performance of the building, so that the consultants receive a bonus and / or pay a penalty based on the actual performance of the completed building.


5.4.4. Timing of design decisions. The timing of design decisions is critical to the success of

integrated design. The cost of making changes increases exponentially with

time as the design becomes more detailed, whereas the opportunity to achieve energy savings declines. This is illustrated in the graph in Fig. 5.1.

Options become more and more limited, and aspects of the

design get “locked in”. This implies that if a change has to be made that does not fit in with decisions already taken, it will be more expensive since it requires numerous changes to other aspects of the design that have proceeded on the assumption of the original decision – effectively turning back the clock and starting over in many aspects of the design. It is therefore worth taking the time to carefully consider the options relating to all the design concepts and how they interact with each other early on in the process, to avoid the need to discard large amounts of detail design work later when a more effective solution is suddenly identified.

Fig. 5.1 Cost / benefit of design change with regard to energy

savings. (Source: ENSAR Group)


5.4.5. Construction. Design of an energy efficient building is only the first

stage. The benefits will only be realised if the construction of the building is carried out in accordance with the design. In practice the quality of work varies greatly from one site to another, and is influenced by many factors, including the quality of the design drawings and specifications, skills of the artisans, contractor’s quality control systems, supervision by the consultants, etc.

The contractor should understand the concepts behind the

design, so that he / she is aware of the purpose for particular specifications and details.

The work on site needs to be regularly inspected and

checked to ensure that details that are particularly relevant to energy performance are properly constructed. This requires appropriate training for the people involved whether this is the resident engineer, clerk of works, architect, or others.

Details that are of particular relevance to energy

performance include:

o Proper installation of damp proofing membranes. o Avoidance of thermal bridges, e.g. in cavity walls. o Installation of insulation according to specifications. o Seals in ductwork and fittings to avoid leaks. o Duct insulation.

5.5. Commissioning. “Commissioning is a systematic process of ensuring that all

building systems perform interactively according to the contract documents, the design intent and the owner’s operational needs.” (The Building Commissioning Guidelines, EDR)

The importance of the commissioning process for a

building has recently been recognised, particularly as a means to reduce operating costs in general and energy costs in particular. It has been found that a carefully managed, comprehensive commissioning procedure for new buildings can greatly reduce the number of problems that are experienced with building systems in the initial period of occupation, and also improve energy performance.

For existing buildings it can be an effective way to identify

systems that are not functioning optimally, and to rehabilitate a building to a state where it is functioning optimally resulting in reduced operating and energy costs.



5.6.1. Books and Papers Energy Design Resources. Design Brief. Performance Based

Compensation. http://www.energydesignresources.com/resource/33/ Energy Design Resources. “The Building Commissioning

Guidelines”. http://www.energydesignresources.com/resource/37/

5.6.2. Web resources EDR. Energy Design Resources http://www.energydesignresources.com/ EERE Building Technologies Program Home Page http://www.eere.energy.gov/buildings/ SBIC. Sustainable Buildings Industry Council. http://www.sbicouncil.org U.S. DOE Energy Efficiency and Renewable Energy (EERE) http://www.eere.energy.gov/ WBDG - Whole Building Design Guide http://www.wbdg.org/

SECTION 6 PLANNING ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES FOR BOTSWANA Revision 1 September 2007

Energy Efficiency Building Design Guidelines for Botswana – Section 6 Planning Page 3

CONTENTS

6. PLANNING 4

6.1. Site Planning 4

6.2. Location. 4

6.3. Orientation. 4

6.4. Surfaces and vegetation. 5 6.4.1. Ground surfaces. 5 6.4.2. Trees and shrubs. 5 6.4.3. Climbers. 6

6.5. Resource Material 7 6.5.1. Books and Papers 7 6.5.2. Web resources 7

6. PLANNING The building in relation to its environment / modifying

the local climate. Included in this section are the location of the building, the

general shape and orientation, and the planning of the immediate surroundings.

6.1. Site Planning Issues relating to climate and energy efficiency need to be

considered from the earliest stages of site planning. Some of the important considerations are as follows: o Location o Orientation o Surfaces and vegetation

6.2. Location. The location of buildings on a site is largely determined by

considerations such as access, planning requirements for site boundary set-backs, views and other constraints. Energy considerations that should be considered include making use of shading from features on or around the plot, such as other buildings or established trees.

6.3. Orientation. The east and west elevations of a building present most

problems related to heating from the sun, since the sun hits these directly in the early morning and late afternoon throughout the year. For this reason buildings should generally present their smaller elevations to the east and west.

Fig 6.1 The sunpath in Gaborone in summer and winter. As plots sizes are reduced to increase plot density, and the

spaces around buildings reduce, it becomes more important that the plots are optimally orientated to allow for the houses on the plot to be aligned with the long axis running east-west.

The opportunity to save energy by correct orientation is

increased if buildings are rectangular, with a high ratio of length to breadth.


6.4. Surfaces and vegetation.

6.4.1. Ground surfaces. The surfaces around a building influence the amount of

reflected direct and indirect radiant heat that falls on the walls. Using surfaces that absorb solar radiation can help to keep buildings cool in summer. Plants are perhaps the most effective, in that they are good at absorbing solar heat, and also cool the air through evapo-transpiration.

There are several species of ground cover plants that can

survive long periods with very little water, and are therefore suitable for locations with restricted water availability.

Suitable species include members of the following families: Crassula Mesembryanthemaceae

Fig 6.2 Trees as shade for buildings.

6.4.2. Trees and shrubs. Plants may also be used to good effect for shading and

windbreaks. The shape and characteristics of the fully grown plant

should be considered in selecting species for a particular location.

In some cases it may be helpful to use deciduous trees that

provide shade in summer but lose their leaves in winter allowing the sun to provide some warmth when it is needed.

Trees that grow well in Botswana include: Fruit trees:

o Paw paw o Banana o Avacodo o Citrus (Lemon, orange, grapefruit) o Guava o Peach o Mulberry

Exotic shade trees:

o Brazilian Pepper tree o Weeping willow o Jacaranda o Neem o Flamboyant

Indigenous trees:

o Morula o Terminalia (Mogonono) o Combretum o Acacia (various species)

6.4.3. Climbers. Climbing plants can be trained over vertical and horizontal

structures to provide both shade and windbreaks.

Suitable species of climbers include the following: o Grapes o Jasmine o Morning Glory o Virginia creeper o Honeysuckle o Bougainvillea

Fig 6.3 Climbers as shade for buildings.



6.5.1. Books and Papers Hamilton, L.B., et. al. 1984. Passive Solar Design Workbook.

BRET. Botswana. Koch-Nielsen, H. 2002 Stay Cool - A Design Guide for the Built



Architects. USA. John Wiley & Sons. Tutt, P. and Adler, D. (Ed.). 1979. New Metric Handbook –


Ward, Sarah. 2002. The Energy Book for urban development in

South Africa. Sustainable Energy Africa. (www.sustainable.org.za)

6.5.2. Web resources Sustainable Energy Africa. http://www.sustainable.org.za

SECTION 7 BUILDING ENVELOPE ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES FOR BOTSWANA Revision 1 September 2007

Energy Efficiency Building Design Guidelines for Botswana – Section 7. Building Envelope Page 3

CONTENTS

7. BUILDING ENVELOPE 5

7.1. Overview 5 7.1.1. Definition. 5 7.1.2. Building envelope and energy performance. 5 7.1.3. Building envelope energy performance in the climate of Gaborone. 6

7.2. Thermal properties of building materials 7 7.2.1. Material properties. 7 7.2.2. Construction properties 8

7.3. Orientation. 10 7.3.1. Reducing solar heat gain in summer. 10 7.3.2. Allowing solar heat gain in winter. 10 7.3.3. Quantifying the effect of orientation. 12

7.4. Characteristics of envelope elements 12 7.4.1. Ground Floor. 12 7.4.2. Roof. 13 7.4.3. Walls. 16 7.4.4. Fenestration. 18 7.4.5. Ventilation. 21

7.5. Codes and Standards 22

7.6. Resource Material 23 7.6.1. Books and reports. 23 7.6.2. Codes and Standards. 23 7.6.3. Web sites. 23

Energy Efficiency Building Design Guidelines for Botswana – Section 7. Building Envelope


7. BUILDING ENVELOPE

7.1. Overview

7.1.1. Definition. The building envelope is defined in this context as those

elements of the building that form the boundary between the indoor environment of a building and the external environment in which it is located for example, the floor, walls, roof, windows, etc.

7.1.2. Building envelope and energy performance. The building envelope is in a sense a filter between the internal and external environments. It serves to protect the indoor spaces from undesirable impacts such as excessive cold, heat, radiation, and wind, while allowing desirable impacts to pass through such as cool breezes on a hot day, warmth from the sun on a cold day, daylight, etc. The building envelope directly influences the energy performance of a building in the following ways: o Resisting undesirable heat transfer. o Allowing desirable heat transfer. o Providing heat storage (delayed heat transfer). o Allowing daylight penetration. o Preventing undesirable light penetration (glare). o Allowing desirable ventilation. o Preventing undesirable ventilation.

These are discussed in more detail in the following sections. Essentially there are two different approaches to envelope design in relation to building energy performance, which are described in more detail in the Section 6, Planning. One approach seeks to isolate the interior of the building as much as possible from the external environment. Insulation is used extensively in all the envelope elements to reduce heat transfer as far as possible. Such buildings rely entirely on air conditioning systems to provide heating or cooling to maintain comfort conditions. This is often referred to as an ‘active’ approach to building energy design. Another approach to building energy design is referred to as “passive” design. This seeks to encourage beneficial interactions between the building and the outside environment, while reducing as far as possible the undesirable interactions. In climates such as that of Botswana, where the average daily temperature is generally close to indoor comfort conditions, this approach tends to make use of thermal mass to reduce the extremes of day and night temperature. Careful use of both insulating and conductive materials as appropriate for different elements of the building prevent or encourage heat transfer when it is useful, and controlled ventilation allows air movement through the building to provide fresh air and help to keep the temperature in the comfort zone. When successful, this approach can allow the external environment to address some or all of the internal loads, reducing the energy required by mechanical systems.


Cooling of the building takes place when heavy elements such as walls absorb heat from the building during the day and release it to outside at night. Ventilation of the building when the outdoor air is cool can also help to cool the building. In winter heat from the sun can be stored in the walls and released into the building at night when heating is needed. When it fails, this approach can lead to high energy consumption if mechanical systems are required to pump heat into or out of thermal mass elements that conflict with the desired internal temperature. Generally buildings such as residential houses with relatively low levels of internal heat gain from occupants, lights and equipment, can be designed using passive principles to achieve comfort conditions for most of the year with little or no mechanical heating or cooling. Buildings with high levels of internal heat gain such as office blocks will generally require mechanical systems to maintain comfort conditions, but there are significant opportunities to reduce the energy consumption with careful design. In the design of energy efficient buildings dominated by internal heat gains particular attention should be given to matching the mechanical systems to the internal loads, and to ensure that control systems are designed and operated to avoid conflict between the mechanical systems and the thermal mass elements of the envelope and internal structure.

7.1.3. Building envelope energy performance in the climate of Gaborone.

Much information is available on how to design energy efficient buildings in climates similar to that of Botswana. In most cases there are however no figures to show the actual impact of such recommendations on building energy consumption, or indoor temperature.

Recently an exercise was carried out to quantify the impact

of different strategies for improving building performance, using computer simulations of three ‘generic’ building types to determine the effect on comfort conditions and energy consumption of changing various building envelope or operational parameters.

The results are summarised in the more detailed discussion

below, and indicate that the local climate is such that some of the ‘conventional wisdom’ relating to energy efficient building design needs to be re-considered.

For buildings with little internal heat gain from occupants

and equipment, it was found that the energy needed for heating in winter is similar to or even greater than the energy needed for cooling in summer. Even in summer, there is opportunity for buildings to loose heat to the environment through the walls and roof at night, and through the floor at all times of day. The result is that the optimal interaction between building and environment is quite complex, and certainly not as simple as providing maximum insulation all round, as may be the case in climates that are generally either too cold or too hot.


7.2. Thermal properties of building materials Thermal properties of building materials include those that are related to a particular material irrespective of its dimensions and location, and properties that relate to the material or groups of materials in a particular configuration as it is used in a building. The first group are described below under ‘material properties’. The second are described under ‘construction properties’.

7.2.1. Material properties. Building materials can conveniently be considered in two categories; opaque and translucent. Opaque materials are those that do not allow transmission of light or thermal radiation. They include typical wall materials such as bricks, concrete, timber, metals and fibre insulation.

The properties of opaque building materials that are most relevant to the thermal performance include the following:

• Thermal conductivity. • Thermal resistivity. • Specific heat capacity. • Density.

Translucent materials are those that allow the transmission of light or thermal radiation. They include materials such as glass and plastics used in windows, curtain walling and skylights. In addition to the properties of opaque materials, it is important to know the transmissivity of translucent materials.

The thermal properties of a number of common building

materials are given in Appendix 1.

7.2.1.1. Thermal conductivity. Thermal conductivity is a measure of the ability of a

material to transfer heat by conduction. It is measured in units of [W/m.K].

7.2.1.2. Thermal resistivity. Thermal resistivity is a measure of the ability of a material

to resist heat transfer by conduction. It is the inverse of thermal conductivity, and is measured in units of [m.K/W].

7.2.1.3. Specific Heat Capacity. Specific Heat Capacity measures the ability of a material to

store heat energy. It is measured in units of [kJ/kg.K]

7.2.1.4. Density. Density measures the mass of a unit volume of material. It

is useful to allow the calculation of heat capacity by volume. It is measured in units of [kg/m3].


Fig. 7.1 Mechanisms of Heat Transfer through the Building

Envelope.

7.2.2. Construction properties A material or group of materials forming a construction

element of a building has properties that are determined partly by the thermal properties of the materials themselves, and partly by the surface characteristics and geometry of the construction.

The properties of construction elements that are most

relevant to thermal performance are as follows: o Overall heat transfer coefficient (U-value). o Overall thermal resistance (R-value). o Heat capacity. o Emissivity (= absorptivity). o Relectivity o Transmissivity.

The thermal properties of a number of common building

construction elements are given in Appendix 1.

7.2.2.1. Overall heat transfer coefficient (‘U’ value). The overall heat transfer coefficient is an approximate

measure that simplifies the calculation of heat transfer through walls, floors and roofs. It combines the heat transfer coefficients for convective and radiative heat transfer from both surfaces with the conductive heat transfer to provide a single overall heat transfer coefficient for the surface. It is somewhat approximate, since the surface heat transfer coefficients for both convective and radiant heat transfer are dependant on the surface temperatures.

It is measured in units of [W/m2.K].

Convection

Solar Radiation

Long wave radiation

Outside Inside

Conduction through a wall

Transmitted Solar Radiation

Long wave radiation

Convection

Solar Radiation

Long wave radiation

Outside Inside

Conduction through a wall

Transmitted Solar Radiation

Long wave radiation

A b s o rb e d s o la rra d ia t io nA b s o rb e d s o la rra d ia t io n


7.2.2.2. Overall thermal resistance (‘R’ value). Overall thermal resistance is the inverse of overall heat

transfer coefficient, and is a measure of the resistance to heat transfer of a building element such as a wall, floor or roof. It is found by adding the individual thermal resistances of each layer of the element, including the surface resistances of the inner and outer surfaces.

It is measured in units of [m2.K/W].

7.2.2.3. Heat Capacity. Heat capacity is a measure of the ability of a building

element to retain heat. Specific Heat Capacity measures the ability of a material to store heat energy.

It is measured in units of [kJ/m3].

7.2.2.4. Combined Heat Capacity and Resistance. It has been suggested that the combined effect of heat

capacity and resistance may be an important criterion for the effectiveness of wall materials. This is defined as the product CR (heat capacity multiplied by overall thermal resistance). It is suggested by Hamilton et. al that a figure of CR=93 [x103sec] may be optimum for the climate in Botswana.

It has units of seconds.

7.2.2.5. Emissivity. Emissivity is a measure of the ability of a surface to emit

radiant heat energy, relative to that of a black surface at the same temperature. It is a dimensionless ratio between 0 and 1. It is equal to absorptivity, which is a measure of the ability of a surface to absorb radiant heat energy.

7.2.2.6. Reflectivity. Reflectivity is a measure of the ability of a surface to reflect

radiant energy. It is a ratio between 0 and 1.

7.2.2.7. Transmissivity. Transmissivity is a measure of the ability of a material to

transmit radiant energy through it. It only applies to translucent materials such as glass. It is a ratio between 0 and 1.


7.3. Orientation.

7.3.1. Reducing solar heat gain in summer. The main factor that determines the optimal orientation for

a building is the daily path of the sun through the sky, and the pattern by which this changes through the year. The main aim is to minimise solar gain on vertical surfaces in summer. The east and west walls are exposed to the sun in the mornings and afternoons respectively, and the area of these walls should be reduced as far as possible. The optimum orientation is therefore with the longer axis of the building running east - west.

7.3.2. Allowing solar heat gain in winter. In buildings that require heating in winter, a further

consideration is to achieve solar heat gain in the winter. The north wall may be designed to receive sunshine in winter, but not in the summer, by arranging shading devices (which may include the roof overhang), that expose the wall to the low winter sun, but shade it from the sun in the spring and autumn when heating is not needed.

Buildings with high internal heat gains such as offices have

very little need for heating even in winter, and in this case solar heat gain should be avoided at all times.

Fig. 7.2 Sunpath in Gaborone in summer and winter. Fig. 7.3 Using the roof overhang to shade the north wall in

summer.


Table 7.1 Effect of orientation on energy consumption for three types of building in Gaborone (EECOB Report: ‘Parametric

simulation of the energy performance of three generic building types in Gaborone, Botswana’)

Indicator Classroom Residential OfficeOrientation E-W (base) N-S E-W (base) N-S E-W (base) N-SSummer (6 months)Heating energy [kWh/m2.yr] 0 0 0.3 0.2 0 0Cooling energy [kWh/m2.yr] 47.3 52.2 15.2 15 99 104Total [kWh/m2.yr] 47.3 52.2 15.5 15.2 99 104% increase over E-W 10.4% -1.9% 5.1%

Winter (6 months)Heating energy [kWh/m2.yr] 3.6 3.5 12.6 13.4 1 1Cooling energy [kWh/m2.yr] 14.2 13.5 1.7 1.7 53 49Total [kWh/m2.yr] 17.8 17 14.3 15.1 54 50% increase over E-W -4.5% 5.6% -7.4%

Annual (12 months)Heating energy [kWh/m2.yr] 1.8 1.7 6.4 6.8 1 1Cooling energy [kWh/m2.yr] 30.8 32.9 8.5 8.4 76 76Total [kWh/m2.yr] 32.6 34.6 14.9 15.2 77 77% increase over E-W 6.1% 2.0% 0.0%


7.3.3. Quantifying the effect of orientation. The effect of changing orientation from E-W to N-S was

simulated for three building types. The effect on energy performance in summer, winter and the full year is summarised in table 7.1.

The overall effect on energy performance is significant for

the classroom building (6.1% increase in annual energy consumption for heating and cooling). It was less for the residential building (2% increase in annual energy consumption for heating and cooling). It had no effect at all for the office building; a winter saving of 8.4% cancelled a summer additional cost of 5.9%.

Total energy consumption is however not the only

important criterion. Windows that admit direct sunshine result in internal areas that are too hot and subject to glare (see Section 9. Lighting). An E-W orientation allows for the larger elevations of a building to face north and south. The north elevation can be more easily protected from the sun than the east and west elevations, and the south elevation is not a problem in this regard.

7.4. Characteristics of envelope elements The design team must find the combination of

characteristics for each building element that best achieves the requirements of the design brief. This requires consideration of the particular conditions that each element is exposed to, in terms of the opportunities and threats that these offer the building.

By considering the optimal characteristics of each element of the building envelope, the most appropriate combination of elements can be achieved. This requires the coordinated input of different specialists to ensure that all the disciplines involved in the building are considered.

Fig. 7.4 Envelope heat flows.

7.4.1. Ground Floor. The average monthly temperature in Gaborone ranges between 25°C in January and 12°C in July. The ground temperature at a depth of 500mm below natural ground level is approximately equal to the average monthly temperature. Buildings generally benefit from ground floors that are in good thermal contact with the ground, by losing heat to the ground.


The simulation for a classroom building indicated an increase in annual heating and cooling energy of 22.9% when 50mm of insulation was provided between the floor and the ground, compared with no insulation.

7.4.2. Roof. Of all the building elements, the roof is most exposed to climatic sources of heat gain and heat loss. Throughout the day the roof is exposed to direct solar radiation, which is potentially the most significant source of heat gain. During the night the roof radiates to the night sky, and also loses heat by convection to the cool night air. The most important strategy is to manage the transfer of heat through the roof structure. For most of the year this is achieved by reducing heat transfer as much as possible. The most effective strategy is to use a reflective surface for the roof finish, such as white painted galvanised steel. This reduces the amount of heat that passes into the roof space in the first place. A similar advantage may be achieved by using a reflective underlay (such as Sisalation) under concrete tiles. Ventilation of the roof space can help to reduce the temperature further, and insulation laid over the ceiling can help to reduce the transfer of heat from the roof space into the occupied rooms below.

7.4.2.1. Lightweight roofs. Lightweight roofs generally consist of an outer

weatherproof layer, typically sheet metal or concrete tiles. This is supported on either steel or timber trusses, with a

ceiling fixed under or over the structure depending on whether this is designed to be seen as part of the indoor spaces.

If the ceiling is suspended under the structure, there is

typically a roof void that may or may not be ventilated to the outside of the building.

Generally the roof should be light coloured to reflect solar radiation, and well insulated to prevent heat gain in the summer and heat loss in the winter. The most cost effective improvement that can be made to a building with a galvanised roof is to paint it white.

Fig 7.5. Roof details.


7.4.2.2. Heavyweight roofs. Heavy roofs are generally constructed as concrete slabs, having significant thermal mass and a degree of insulation within one element. Additional insulation is needed to avoid excessive heat gain to the building in summer and heat loss in winter. The positioning and capacity of this insulation is important, and again there are a number of options. Insulation may be added above the slab. This will reduce heat exchange between the slab and the outdoor environment, and maximise the effectiveness of the slab as a heat capacitor for the building, reducing fluctuations. As with all thermal mass elements, there is the danger that this may be in conflict with the mechanical heating and cooling system leading to excessive energy consumption. In a building with no air-conditioning system this may be beneficial in reducing temperature fluctuations, and moderating the indoor temperature to a reasonably comfortable average of outdoor maximum and minimum temperatures. This depends on many other factors, including internal loads and the performance of other building elements. Insulation may be added below the slab. Providing insulation below the slab will moderate the effect of the thermal mass. Depending on the relative impact of

daytime radiant heat gain and night time radiant cooling, the underside of the slab may be close to the indoor comfort temperature for much of the time. This may be a good solution for buildings that are air-conditioned, since the heat transfer through the insulating element will be further reduced by the smaller temperature difference across this element.

7.4.2.3. Simulation of roof interventions. The three storey commercial building showed an annual energy saving of 4.8% with a white roof compared to a galvanised roof. In the classroom building, the equivalent saving was 46%.

The simulation for a double storey residential house showed that increasing the ceiling insulation from 50mm to 150mm lead to an energy saving of 2.7%. However this was fitted with a concrete tile roof finish with Sisalation underlay which is reasonably efficient to begin with. For the classroom building the saving by providing 100mm insulation was 43.6%. An insulated concrete roof resulted in an energy saving of 52.9% in the classroom building, compared with the galvanised steel roof with no ceiling insulation. In the residential building the concrete roof resulted in a 3.6% increase in energy cost, and similarly in the office building annual energy cost was increase by 5%.


Table 7.2 Effect of roof colour and insulation on energy consumption of three building types in Gaborone (EECOB Report: ‘Parametric


Indicator Classroom Residential OfficeRoof Galv

uninsulat'd (base)

White metal

100mm insulation

Conc. tiles (base)

White metal

+100mm Insul'n

Green metal (base)

White metal

+100mm Insul'n

Summer (6 months)Heating energy [kWh/m2.yr] 0 0.1 0 0.3 0.4 0.3 0 0 0Cooling energy [kWh/m2.yr] 47.3 24.3 27 15.2 14.1 15 99 94 97Total [kWh/m2.yr] 47.3 24.4 27 15.5 14.5 15.3 99 94 97% increase over base -48.4% -42.9% -6.5% -1.3% -5.1% -2.0%

Winter (6 months)Heating energy [kWh/m2.yr] 3.6 5.7 3.1 12.6 13.1 12.1 1 1 1Cooling energy [kWh/m2.yr] 14.2 5.4 6.6 1.7 1.5 1.7 53 50 54Total [kWh/m2.yr] 17.8 11.1 9.7 14.3 14.6 13.8 54 51 55% increase over base -37.6% -45.5% 2.1% -3.5% -5.6% 1.9%

Annual (12 months)Heating energy [kWh/m2.yr] 1.8 2.9 1.6 6.4 7.2 6.2 1 1 1Cooling energy [kWh/m2.yr] 30.8 14.8 16.8 8.5 7.8 8.3 76 72 76Total [kWh/m2.yr] 32.6 17.7 18.4 14.9 15 14.5 77 73 77% increase over base -45.7% -43.6% 0.7% -2.7% -5.2% 0.0%


7.4.3. Walls. In designing the walls consideration should be given to the

different conditions that they will be exposed at each time of day and season depending on their orientation. In some cases there are conflicting opportunities or constraints at different times of year, e.g. a west facing wall may benefit from the heat of the sun in winter, but suffer in the summer. It appears that different solutions are appropriate for different types of building.

7.4.3.1. East and West Elevations. Walls that face the east and west should generally be as

well insulated as possible, to prevent summer heat gain from the low morning and evening sun.

These elevations can benefit from shading from trees,

shrubs or climbing plants. If these are deciduous, the building can benefit from morning and afternoon heat gain in the winter months while being protected in the summer. For buildings with large internal loads that require cooling in winter, evergreen trees or climbers would be more appropriate. (See Section 6. Planning).

7.4.3.2. North Elevation. The north elevation receives sunshine during the winter

months, with the sun at an average midday altitude of 42° in June. In midwinter the sun rises in the northeast and sets in the northwest. During this time, the north elevation is therefore exposed to quite large amounts of direct solar radiation that can provide some useful heat gain in this cold period for buildings such as residential houses that require heating. Buildings such as offices or classrooms that have

Fig 7.6. Sunpath in Gaborone in summer and winter. very little need for heating should have the north walls

protected from the sun if possible. The heating season typically begins in April and ends in

August. At these times of year the midday sun reaches an altitude of about 55°. It now rises and sets about 15° north of the east – west axis so that it sees little of the north wall in the early morning and late afternoon. Shading of windows on this elevation should therefore be designed to protect the windows when the sun is above an altitude of about 60°.


Table 7.3 Effect of wall insulation on energy consumption for three building types in Gaborone (EECOB Report: ‘Parametric


Indicator Classroom Residential OfficeWall insulation 220mm

baseins. cavity ins. mass 220mm

baseins. cavity ins. mass 220mm

baseins. cavity ins. mass

Summer (6 months)Heating energy [kWh/m2.yr] 0 0 0 0.3 0.1 0.1 0 0 0Cooling energy [kWh/m2.yr] 47.3 51.8 52.5 15.2 15.1 15.1 99 101 102Total [kWh/m2.yr] 47.3 51.8 52.5 15.5 15.2 15.2 99 101 102% increase over 220mm 9.5% 11.0% -1.9% -1.9% 2.0% 3.0%

Winter (6 months)Heating energy [kWh/m2.yr] 3.6 2.6 2.5 12.6 4.7 3.8 1 0 0Cooling energy [kWh/m2.yr] 14.2 16 16.3 1.7 1.8 1.9 53 60 62Total [kWh/m2.yr] 17.8 18.6 18.8 14.3 6.5 5.7 54 60 62% increase over 220mm 4.5% 5.6% -54.5% -60.1% 11.1% 14.8%

Annual (12 months)Heating energy [kWh/m2.yr] 1.8 1.3 1.3 6.4 2.4 2 1 0 0Cooling energy [kWh/m2.yr] 30.8 33.9 34.4 8.5 8.5 8.5 76 81 82Total [kWh/m2.yr] 32.6 35.2 35.7 14.9 10.9 10.5 77 81 82% increase over 220mm 8.0% 9.5% -26.8% -29.5% 5.2% 6.5%


7.4.3.3. South Elevation. The south elevation receives only a glancing blow from the

sun in the early morning and late afternoon in mid summer. By midday the sun is almost directly overhead. The south wall may therefore be a good opportunity to introduce thermal mass to increase the thermal capacitance of the building.

This is the best elevation on which to locate windows for

daylighting, since these receive little or no direct sunlight.

7.4.3.4. Simulation of wall interventions. The simulation showed that for the residential building type

substantial energy savings can be achieved by using insulated cavity walls, or insulated mass walls in place of standard 220mm walls. Increased mass walls with insulation are marginally better than insulated cavity walls, but the improvement was marginal.. The benefit was almost entirely in reduced heating energy in winter. When the building requires cooling, the walls actually help by absorbing heat from the inside during the day and transferring it to the outside at night. As a result, insulated walls resulted in increased energy consumption for both the classroom and office building types, where cooling energy greatly exceeds heating energy. (See Table 7.3)

7.4.4. Fenestration. The primary objective in designing the fenestration for a

building should be to maximise the benefits, namely: o Daylighting. o Views. o Ventilation.

while minimising the negative qualities:

o Glare. o Radiant heat gain. o Conductive and convective heat gain and heat loss.

7.4.4.1. Daylighting. The subject of daylighting is covered in more detail in

Section 8. Lighting. The objective of window design with respect to lighting

should be to provide as much of the indoor lighting requirement with daylighting as is possible without compromising other energy efficiency considerations. In particular this will require consideration of the heat transfer properties of the glazing. This is an element that may justify some cost analysis, as there is a clear relation between cost and thermal effectiveness. Improved insulation can be achieved using various configurations of multiple glazing, and selective coatings, the cost of which is generally more the greater the effectiveness of the product. Selective coatings may also reduce the light penetration, so that in some cases the same quantity of daylight may be achieved with smaller clear windows as


with larger coated windows, with lower cost and overall heat loss.

Typical properties of different types of glass available in

Southern Africa are given in Appendix x. The shading coefficient is the ratio of Total Solar Energy

Transmission of a glass compared to the Total Solar Energy Transmission for ordinary 3mm glass.

The ratio of Total Visible Light Transmission compared to

Total Solar Energy Transmission has been included to give a comparison of which glass is most effective at transmitting maximum light with minimum energy.

7.4.4.2. Views. Views of the outdoor environment have an important

impact on the quality of the indoor environment for a variety of occupations, and can significantly improve people’s productivity.

7.4.4.3. Simulation of window interventions. Various interventions were simulated on the three types of

buildings, including shading of north facing windows, double glazing, increasing the glazing ratio, and using specialised glass.

Double glazing was found to have very little effect on

energy consumption, with an annual savings as follows: o Residential 3.6% o Classroom 0.3% o Office 0.0%

North window shading has some benefit for classrooms and office buildings, but not for the residential building, with annual energy savings as follows: o Residential -0.3% (increase in energy) o Classroom 4.8% o Office 6.0%

Increasing the glazing area from 20% to 40% of external

wall area resulted in substantial increases in energy consumption for all building types. This was somewhat mitigated by using ‘Coolvue’ glass with a selective coating, but overall energy consumption was still between 10% and 30% higher than in the base case. (See Table 7.4.)

It is recommended that glazing areas are generally kept to

no more than about 30% of external wall area. Higher glazing levels in air conditioned buildings will lead to excessive consumption of energy unless sophisticated design measures such as ventilated double facades or solar control glass with external shading are employed.

In buildings that are not airconditioned, large amounts of

glazing will result in high indoor temperatures and uncomfortable buildings.


Table 7.4 Effect of glazing interventions on energy consumption for three building types in Gaborone (EECOB Report: ‘Parametric simulation of the energy performance of three generic building types in Gaborone, Botswana’)

Indicator Classroom Residential OfficeWindow glazing 20% clear

(base)40% clear 40%

Coolvue10% clear

(base)40% clear 40%

Coolvue20% clear

(base)40% clear 40%

CoolvueSummer (6 months)Heating energy [kWh/m2.yr] 0 0 0 0.3 0.3 0.3 0 0 0Cooling energy [kWh/m2.yr] 47.3 53.3 52.6 15.2 21.4 19.9 99 106 102Total [kWh/m2.yr] 47.3 53.3 52.6 15.5 21.7 20.2 99 106 102% increase over base 12.7% 11.2% 40.0% 30.3% 7.1% 3.0%

Winter (6 months)Heating energy [kWh/m2.yr] 3.6 3.7 3.6 12.6 10.5 11.6 1 1 1Cooling energy [kWh/m2.yr] 14.2 18.5 18.3 1.7 4 3.6 53 66 60Total [kWh/m2.yr] 17.8 22.2 21.9 14.3 14.5 15.2 54 67 61% increase over base 24.7% 23.0% 1.4% 6.3% 24.1% 13.0%

Annual (12 months)Heating energy [kWh/m2.yr] 1.8 1.9 1.8 6.4 5.4 5.9 1 1 1Cooling energy [kWh/m2.yr] 30.8 35.9 35.5 8.5 12.7 11.8 76 86 81Total [kWh/m2.yr] 32.6 37.8 37.3 14.9 18.1 17.7 77 87 82% increase over base 16.0% 14.4% 21.5% 18.8% 13.0% 6.5%


7.4.5. Ventilation. Ventilation in buildings serves two main purposes;

improvement of air quality, and improvement of indoor climate.

Ventilation is the primary means of improving air quality, by removing polluted air and replacing this with better quality outdoor air. This of course assumes that the outdoor air is of an adequate quality to achieve this. Where this is not the case, filtration may be required to achieve an acceptable level of indoor air quality (see Section 4. Indoor Environment).

Ventilation can also be used as a means of improving

indoor climate under favourable conditions. Ventilation may be achieved by openings in the walls or

roof that are controlled by the occupants, such as doors and windows, or by mechanical means using fans and ducting.

Design of ventilation systems must take into consideration

the potential problem of drafts which can cause localised discomfort as well as creating problems such as paper blowing around.

The issue of security also needs to be considered if

windows are to be left open at night to take advantage of cool night air.

7.4.5.1. Simulation of ventilation interventions. Simulations were carried out to quantify the effect of using

ventilation to modify indoor temperature when the outdoor air temperature is beneficial. The annual energy savings for the three types of building were as follows: o Residential 27.0% o Classroom 5.1% o Office 27.8%

Even stimulating views -- widely argued to be distracting for students and workers alike -- seem to have a positive effect on performance. A 2003 energy commission study of the Fresno School District found that complex window views -- with greenery or people and distant landscapes -- supported better learning results. Similarly, a study of the effects of views at the Sacramento Municipal Utility District's customer service call center found that better views were consistently associated with better performance. Workers enjoying the best possible views processed calls 7 to 12 percent faster than those with no views. Better views have also been associated with better health conditions. In one study, computer programmers with views spent 15 percent more time on their primary task, while those without views spent 15 percent more time chatting on the phone or to one another. Healthy buildings pay for themselves Daylight, views are more than mere amenities. Carol Lloyd Sunday, July 23, 2006 San Francisco Chronicle


For the office building type, ventilation has the greatest

potential to reduce energy cost of all the interventions to the building envelope that were simulated. Some practical problems do need to be addressed in order to achieve this level of ventilation in a controlled manner, without causing problems with draft.

7.5. Codes and Standards Codes have been adopted in a number of countries that

define minimum energy performance standards for different classes of buildings. These typically include specific requirements for building envelope elements.

An example of such a code is the ASHRAE Standard 90.1

2001: Energy Standard for Buildings except Low Rise Residential Buildings.

This specifies maximum permissible U-values and

minimum R-values for various envelope components, based on the climate in which the building is situated. Climate is defined in terms of heating and cooling degree days.

Appendix 3 gives details of some of the requirements of

this standard for Pretoria, together with the relevant climatic data.



7.6.1. Books and reports. ASHRAE Standard 90.1-2001. Energy Standard for Buildings

except Low Rise Residential Buildings. Energy Code for New Federal Commercial and Multi-Family High

Rise Residential Buildings; Final Rule, October 2000. Department of Energy, Office of Energy Efficiency and Renewable Energy, US Government.

EECOB Report: ‘Parametric simulation of the energy performance

of three generic building types in Gaborone, Botswana’. Department of Energy, Government of Botswana, January 2007.


BRET. Botswana. Hunn, B.D. (ed) 1996. “Fundamentals of Building Energy

Dynamics.” Massachusetts Institute of Technology. Koch-Nielsen, H. 2002 Stay Cool - A design Guide for the Built



Architects. USA. John Wiley & Sons. Rogers, G.F.C., Mayhew, Y.R. 1967. “Engineering

Thermodynamics Work and Heat Transfer” Longman.

Tutt, P. and Adler, D. (Ed.). 1979. New Metric Handbook –


7.6.2. Codes and Standards. ASHRAE Standard 90.1-2001. Energy Standard for Buildings

except Low Rise Residential Buildings. Energy Code for New Federal Commercial and Multi-Family High

Rise Residential Buildings; Final Rule, October 2000. Department of Energy, Office of Energy Efficiency and Renewable Energy, US Government.

Malaysian Standard MS1525: 2001. Code of Practice on Energy

Efficiency and Use of Renewable Energy for Non-Residential Buildings. Department of Standards, Malaysia.

Guam Energy Code, American Samoa and Guam Energy Code

Development Project. January 25, 2000

7.6.3. Web sites. Soil Temperature Variations With Time and Depth http://soilphysics.okstate.edu/toolkit/temperature/index0.html PG Glass http://www.smartglass.co.za ASHRAE American Society of Heating, Refrigerating and Air-conditioning Engineers. http://www.ashrae.org/


CIBSE Chartered Institute for Building Services Engineers http://cibse.org EDR. Energy Design Resources http://www.energydesignresources.com/ EERE Building Technologies Program Home Page http://www.eere.energy.gov/buildings/ SBIC. Sustainable Buildings Industry Council. http://www.sbicouncil.org SQUARE ONE environmental design, software, architecture, sustainability. http://squ1.org/wiki/Concepts WBDG - Whole Building Design Guide http://www.wbdg.org/

SECTION 8 MECHANICAL SYSTEMS ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES FOR BOTSWANA Revision 1 September 2007

Energy Efficiency Building Design Guidelines for Botswana – Section 8 Mechanical Systems Page 3

CONTENTS

8. MECHANICAL SYSTEMS (HVAC) 5

8.1. Overview 5

8.2. Building heating & cooling loads 5 8.2.1. Fabric heat gains 5 8.2.2. Internal heat gains 6 8.2.3. Passive Cooling 6

8.3. HVAC system design. 7 8.3.1. Design Brief. 7 8.3.2. Zoning. 7 8.3.3. Selecting the type of system. 7 8.3.4. Sizing the system. 7

8.4. Heating, ventilation and air conditioning systems (HVAC) 8 8.4.1. Naturally Ventilated Buildings 9 8.4.2. Semi-passive buildings 9 8.4.3. Mixed-mode Buildings 10 8.4.4. Comfort Cooling / Unitary Systems 10 8.4.5. Air Conditioning / Centralised Systems 10

8.5. Ventilation & Cooling Systems 11 8.5.1. Evaporative Cooling 11 8.5.2. Local Comfort Cooling 12 8.5.3. Constant Volume Ventilation systems 13 8.5.4. Variable Air Volume Ventilation systems 14 8.5.5. Chilled Beams/Chilled Slabs 14 8.5.6. Fan Coil Units 14

Energy Efficiency Building Design Guidelines for Botswana – Section 8 Mechanical Systems

8.5.7. Desiccant Cooling 15 8.5.8. Groundwater cooling / Ground source heat pumps 15

8.6. Ventilation Equipment 16 8.6.1. Fans and AHUs 16 8.6.2. Performance Standards - Ventilation 17

8.7. Refrigeration and Cooling Equipment 17 8.7.1. Cooling Towers/Water Cooled Chillers 17 8.7.2. Absorption Chillers 18 8.7.3. Air Cooled Chillers 18 8.7.4. Thermal Storage 18 8.7.5. Performance Standards - Cooling 19

8.8. Heating Equipment 19

8.9. Controls 19

8.10. Commissioning & Handover 20

8.11. Maintenance & Replacement 20

8.12. Resource material 21 8.12.1. Books and papers 21 8.12.2. Codes and Standards. 21 8.12.3. Websites. 21


8. MECHANICAL SYSTEMS (HVAC)

8.1. Overview This section addresses the subject of mechanical systems in

buildings and the heating and cooling loads that they are designed for. It begins by discussing the loads, which include both external loads relating to the influence of the external climate through the building envelope as well as internal loads generated by the users of the building, their lighting, and other equipment.

It is not the intention to present comprehensive design

guidelines, but rather to highlight opportunities for increased energy efficiency related to the classes of building covered by these Guidelines.

The section is structured with chapters 8.2 and 8.3

providing background information on thermal loads and design of HVAC systems. Chapter 8.4 discusses HVAC system selection, and Chapter 8.5 outlines a range of different HVAC systems available. The following chapters 8.6, 8.7 and 8.8 include detailed advice on ventilation, cooling and heating systems respectively. Chapters 8.9 and 8.10 address controls, commissioning and maintenance of systems.

8.2. Building heating & cooling loads In Botswana in most large buildings such as offices there is

very little requirement for heating even in the winter period.

The cooling load of a building in summer will depend on: a) the desired internal temperature (cooling a building to

20°C will use a lot more energy than cooling a building to 24°C) – see design criteria in Section 4, Indoor Environment.

b) the amount of fresh air ventilation delivered to the occupants – see design criteria in Section 4, Indoor Environment.

c) fabric heat gains - the amount of heat entering the building from outside (through windows, walls, roof and by uncontrolled air infiltration)

d) internal heat gains – the amount of heat generated inside the building by the occupants, equipment such as computers, lighting etc.

e) amount of passive cooling available (from thermal mass etc)

8.2.1. Fabric heat gains There are three main sources of heat gain through the

building envelope a) Solar gain through windows – solar radiation passing

through windows will cause very high heat gains if windows are too large and without external shading. Gain can be reduced using solar coated glazing (see Section 7, Building Envelope). In a well designed building, it should be possible to limit gains to around 25W/m² (floor area) or less. In a poorly designed building with extensive glazing, solar gains may easily be over 100W/m².

b) Conduction gain through windows, walls and roof – when it is warmer outside than inside, heat is conducted through the building fabric. The amount of heat


conducted depends on the insulation properties of the construction. Insulation is particularly important in the roof. With roof insulation and a ventilated cavity it should be possible to reduce conduction gains to around 5 W/m² or less.

c) Uncontrolled air infiltration – warm outside air entering the building through gaps in the envelope, cracks, open windows, open doors etc will heat up the internal spaces. Any building with cooling should always be constructed so as to be as airtight as possible (allowing the amount of fresh air to be controlled). With poor construction techniques, infiltration can lead to gains of well over 50 W/m². With good airtight construction, it should be possible to limit these to 5 W/m².

8.2.2. Internal heat gains Sources of internal heat gains will depend on the use of the

building, but typically include a) Occupants – people generate heat from their bodies -

See Section 4, Indoor Environment for further details. The greater the occupant density (ie people/m²) the greater this heat gain will be. Typical values for an occupant density of 1 person/12m² would be 8W/m²

b) Lighting – fluorescent lighting generates much less heat than intumescent lighting and will therefore reduce cooling loads. Typical values are 12W/m² for an efficient fluorescent scheme, 50W/m² or more for a scheme with extensive dichroic and other decorative lights.

c) Office equipment – computers, photocopiers etc all give off heat. Modern LCD flat screens give off much less heat than CRT monitors and should therefore be

encouraged. Typical values for an office would be 10-15 W/m². Note that the amount of heat given off by a piece of equipment is usually much less than the rated power requirement (which is the peak power requirement).

d) Catering equipment. e) HVAC equipment – equipment such as fan coil units

located inside the building give off some heat.

8.2.3. Passive Cooling Heavyweight buildings with exposed high density finishes

such as concrete ceilings or tiled floors absorb heat during the day and radiate it out during the night. This has the effect of stabilising internal temperatures and means that less active cooling is required to maintain comfortable conditions. To analyse the extent of cooling achieved normally requires a computer simulation, but can be equivalent to 15-20 W/m² in a well designed building.


8.3. HVAC system design. There are substantial opportunities for reducing energy

consumption in buildings in Botswana by optimising HVAC system design for energy efficiency. This will require a move away from current designs which are directed more towards ensuring that there is always excess capacity.

8.3.1. Design Brief. It is vital that a clear brief is agreed between the designers

and client. This will include: - required internal temperatures and whether occasional

periods outside these conditions are acceptable. - occupant numbers or density (m²/person). - hours of occupation. - equipment to be used in the space. The designer must then agree the appropriate external design conditions (either a design summer day or preferably a weather file to be used for thermal simulation) (see Section 3, Climate).

8.3.2. Zoning. Effective zoning of the building for HVAC design is

critical to achieving energy efficiency. Generally the zoning should match the thermal

performance of different parts of the building. Large buildings are often divided into an internal zone, and a number of perimeter zones for each floor. The internal zone will tend to be dominated by internal loads, while the

perimeter zones experience the combination of internal loads and envelope loads. These may vary through the day, with the impact of solar radiation on the different elevations of the building. At certain times of year it may be that one zone requires heating while another requires cooling, which offers the opportunity to transfer heat from one zone to another in the same building.

8.3.3. Selecting the type of system. Some advice on selection of systems is given in the

following section. Many factors need to be considered, including the following: o Energy efficiency. o Resilience in the event of breakdowns. o Maintenance and repair capabilities.

Clearly in a financial data centre or food processing

factory, the implications of failure of the systems and overheating are likely to be much more severe than in say a college, and the design will have to reflect this.

8.3.4. Sizing the system. Accurate sizing of the HVAC system can lead to

substantial savings both in initial capital cost and operating cost.

Design Day Calculations – here a design day is chosen

(typically the hottest day in a “typical” year), and the various heat gains into the space calculated at each hour of the day. The cooling system is then designed to meet the highest heat gain. Such methods tend to lead to oversizing of equipment, but are widespread not least since occupants


will rarely complain if a system is oversized but will complain if the building overheats. A study in Ireland found that a large commercial building in Dublin had been designed with between 28% - 90% higher capacity systems using static methods than was required when dynamic simulation was used to size the system.

Computer simulations – here the building is modelled

typically every 10-60 minutes and heat flows in and out of the building analysed. Either one design day is taken (which is repeated several times to establish constant results) or else a whole summer period of typical weather data is used. This type of modelling allows the passive cooling effects of the building to be taken into account, and allows much more accurate sizing. Computer simulation is essential to predict the performance of low energy, passive or semi-passive buildings. Refer Section 11, Simulation

8.4. Heating, ventilation and air conditioning systems (HVAC)

The mechanical systems in a building provide ventilation,

cooling and heating to maintain comfortable conditions. To achieve good energy efficiency, the selection of the type

of mechanical systems in a building has to be decided at the very early concept stages of the design (See Section 2, Design Brief and Section 5, Design and Construction Process).

“Low Energy” cooling systems typically have limited

capacity for cooling, and will therefore only be successful if the building envelope, building structure and indeed the use of the building is controlled within strict limits. It is essential that these limitations are understood by the client and the rest of the design team.

The usual way to represent this is in terms of the system’s

ability to provide cooling in Watts/m². Note that this is approximate only.


Fig. 8.1 Selection of cooling systems (Source: ARUP)

8.4.1. Naturally Ventilated Buildings There are many examples of naturally ventilated buildings

in Botswana such as houses, schools, offices, etc. many of which remain reasonably comfortable throughout the year. Such buildings use much less energy than air conditioned buildings, and the design of such buildings is therefore to be encouraged.

To remain comfortable in summer, naturally ventilated

buildings rely on passive cooling from the use of thermal mass. Typically this involves exposed concrete ceilings

and/or heavyweight floor finishes. For this to work the building must be ventilated at night so that heat absorbed during the day is released. Concrete ceilings must have insulation above them so that they are not heated up by the sun.

Windows must be openable and controllable such that they

can be opened a small amount without causing large drafts. Ceiling fans can be used to provide air movement on hot

days which improves comfort conditions, at the expense of increased energy use.

For a naturally ventilated building to be successful in

Botswana, windows should be designed to avoid all direct sunlight into the building during summer months, and internal heat gains from lighting and equipment must also be kept very low.

8.4.2. Semi-passive buildings It is possible to use fans to assist the ventilation process and

increase the amount of cooling available from the structure. Typical systems include blowing air through the centre of extruded concrete beams (e.g. Termodek system), basement thermal labyrinths or using chambers filled with rocks as a thermal store.

By using a fan it is easier to guarantee night time

ventilation, and it is also easier to control the volumes of fresh air being delivered during the day, reducing the risk of temperatures being too cold early in the morning. For


these buildings to be successful, it is essential that they are made airtight.

8.4.3. Mixed-mode Buildings Here buildings are provided with cooling systems, but are

designed such that this can be switched off and the building operated as a naturally ventilated building when outside conditions allow. In Botswana there is a large part of the year when buildings could be operated like this, thus saving considerable amounts of money. However, to be successful, buildings have to be carefully designed with all of the features of a naturally ventilated building outlined above. Unless the system is simple to operate and the occupants understand it, there is a risk that the cooling systems will be used all year round.

8.4.4. Comfort Cooling / Unitary Systems It may be that only certain of the rooms within a building

require cooling (for example computer rooms, meeting rooms etc). Unitary systems (such as dx split units) may be suitable where only a few rooms need to be conditioned.

8.4.5. Air Conditioning / Centralised Systems Generally centralised air conditioning systems are likely to

be suitable for buildings that require conditioning throughout most of the building, and have relatively high internal loads, such as multi-storey office buildings which have been designed with large areas of glazing (gains of 75W/m² and over). Different types of centralised systems are described in the following section.


8.5. Ventilation & Cooling Systems The choice of ventilation & cooling system will depend on

many factors, including: o Capital cost o Running and replacement costs o Energy use o Comfort level requirements o Maintenance requirements o Adaptability and flexibility o Space requirements (for plant rooms and risers)

The following gives some guidance on what systems could

be considered.

8.5.1. Evaporative Cooling The principle behind evaporative cooling is that when

water evaporates, it takes heat from the surrounding air. This makes the air cooler, but also more humid. Evaporative cooling systems may be suitable for rooms with lower heat gains and/or where internal design conditions are less stringent, for example classrooms, clinic waiting areas, shops and residential houses. They may in some cases be combined with a few unitary systems, e.g. in a clinic it may be appropriate to use evaporative cooling for general waiting areas and corridors, and have a split units in the consulting rooms.

Various types of evaporative cooling can be used:

Fig 8.2 Downflow evaporative cooling unit a) Local Downflow units These units are typically roof mounted, and are widely used

in retail spaces in Botswana. Air is drawn downwards by a fan over pads which are continually wetted with water. The cool, moist air is then supplied to the space.

b) Evaporative Coolers incorporated within AHUs i) Direct The units are designed to fit within air handling units

(typically after the supply fan), and humidify the air either using wetted pads or spraying a fine mist of water into the air. Typically water treatment is required to ensure that the sprays do not clog and that health risks are minimised. This is because it is likely that building occupants will inhale the water droplets.

As with downflow units, it is essential that the units are maintained and cleaned properly.


ii) Indirect In these units the humidification occurs on the extract air. A

thermal wheel in the AHU then transfers some cooling from the cooled extract air to the supply air. The advantage of this arrangement is that the supply air is cooled but not humidified. Disadvantages are the increased complexity and decreased efficiency.

iii) Two stage A number of variations of basic evaporative coolers exist.

In one, the water is first circulated in a dry coil in front of the incoming air, to cool the air without humidification. The slightly warmer water is then trickled over a core and evaporated into the incoming air.

Fig. 8.3 Two stage evaporative cooler AHU

c) Other ways of taking advantage of evaporative cooling include fountains, water features etc. However, these are usually less controllable and effective than purpose designed equipment.

8.5.2. Local Comfort Cooling

Fig. 8.4 VRV outdoor unit and indoor concealed unit a) Variable Refrigerant Volume (VRF/VRV) These systems comprise several indoor units (cassettes or

concealed ducted units) connected to a large condenser unit(s) typically mounted on the roof. The units are linked with refrigerant pipework. Care should be taken when routing refrigerant pipework through spaces where people may be sleeping, and depending on the volume of refrigerant, leak detection may be required in such spaces.

Refrigerants with a zero ozone depletion potential and low

global warming potential should be used and R22 should be avoided.


Fig. 8.5Split system outdoor unit and indoor cassette unit b) Direct Expansion (DX) split units (heat pumps) These systems should be used with a separate system

supplying fresh air (typically into the back of the unit). Opening doors and windows to provide fresh air will waste significant energy.

Again, refrigerants with a zero ozone depletion potential

and low global warming potential should be used and R22 should be avoided.

Although relatively easy to install and maintain, these units

have significantly higher energy use than other options for cooling.

8.5.3. Constant Volume Ventilation systems In these systems, a central air handling unit provides all the

air required for cooling as well as for fresh air. This means the AHU air volumes will typically be in the order of 50-100 litres/sec/person. The AHU is equipped with filters and a cooling coil (either using chilled water or refrigerant) and serves a single zone of the building, so that all areas in that zone have similar cooling/heating loads and hours of operation.

When the air temperature outside is hot, the majority of air

in the AHU is recirculated, with only a % of fresh air (typically 10 litres/sec/person) introduced. This minimises the energy used cooling the fresh air. However, when outside temperatures are below say 20°C, the AHU can use 100% of outside air, and this provides “free cooling” reducing the number of hours that chillers are required to run.

Reducing the pressure drop through ducts and grilles will

greatly reduce the energy used by the fan. A typical standard to aim for is a specific fan performance of 3 W/l/s.

One way of achieving very low pressure drops is to use a

raised floor to supply the air. Air is blown from the AHU in to the raised floor (typically at least 300mm high) and allowed out via diffusers in the floor.


8.5.4. Variable Air Volume Ventilation systems These systems are similar to constant volume system, but

are able to vary the volume of air supplied to each room. This requires more complex controls and automated

dampers (VAV boxes) on each zone. The advantage of such a system is that it can cope with some rooms with higher heat gains than others, and the air-conditioning can be turned off in a room if it is not in use.

8.5.5. Chilled Beams/Chilled Slabs These systems are used in conjunction with an AHU which

supplies the minimum fresh air requirement. They do not use fans to distribute cooling, and so are potentially more efficient than fan coil solutions.

Fig 8.6 Chilled ceiling installation and active chilled beam Chilled beams consist of metal plates attached to the ceiling

through which chilled water is passed. The surface then provides cooling both by convection and radiation. Active

chilled beams are combined with the air supply system to increase the cooling available. Care must be taken to avoid condensation forming on the plates, which limits how cold the surfaces can be made, unless the supply air is carefully controlled and dehumidified.

Chilled slabs are case with plastic pipework in situ, and

chilled/cool water circulated through the slab. Such a system might be appropriate for a building which is naturally ventilated to improve comfort at peak summer conditions. However, control of the system is not straightforward.

8.5.6. Fan Coil Units Fan coil units are local fans with a filter and cooling coil

which recirculate and cool/heat air locally. They are typically mounted either on the perimeter (under windows) or in a false ceiling. They provide very accurate local control of temperature, but are not very energy efficient due to the energy required to run the fan, pump the chilled water etc. Fresh air is typically supplied by an AHU.


Fig 8.7 Ceiling concealed fan coil unit and typical perimeter fan

coil Recent improvements in fan coils include the use of EC

(Electronically commutated) motors which use significantly less energy than conventional AC motors.

8.5.7. Desiccant Cooling A variation on evaporative cooling is desiccant cooling. A

thermal wheel in an AHU is coated with desiccant (a material which absorbs moisture). The supply air is sprayed with water (cooling it and making it more humid) and then passes through the desiccant wheel which reduces its humidity. Depending on the resulting humidity, it may be possible to lower the air temperature further by spraying with water again. The extract air is heated before it passes through the desiccant wheel in order to recharge (dry out) the desiccant.

8.5.8. Groundwater cooling / Ground source heat pumps The ground and groundwater remain at a relatively cool

temperature throughout the year. If groundwater is available it can be used as a cooling medium (and the warmed water then used for other purposes).

Ground source heat pumps operate by pumping water

through a loop of pipe which is buried in a borehole or similar.

Because the ground stays at a constant temperature all year

round, it can be used for cooling in summer and heating in winter. These systems are becoming more common in Europe but are relatively complex and have a high initial capital cost for the installation of boreholes etc.


Fig 8.8 Guide to system selection (BSRIA AG15/2002 Illustrated

Guide to Building Services)

8.6. Ventilation Equipment For an energy efficient ventilation system, consideration is

needed of: o Evaporative cooling where appropriate. o Variable speed motors for fans. o Variable air volume systems. o High efficiency motors for fans. o Insulation to air supply ducts. o Optimised AHU and duct sizes and design of fittings

to reduce friction losses. o Optimised zoning and controls o Design details and construction supervision to avoid

leaks and flow restrictions. o metering of electrical consumption of major plant

8.6.1. Fans and AHUs

Fig. 8.9 Typical AHU EC and DC motors use less energy than standard AC

motors, and are of particular benefit in smaller fans (eg


extract fans, fan coil units etc). Generously sized AHU (air handling units) will use less energy due to lower air velocities. Typically a cooling coil should be selected at air velocity < 2.5m/s and large ducts used (velocity in ducts typically < 8m/s) to minimise fan power. Filters should also be regularly cleaned and replaced since the pressure drop increases as the filters become blocked.

8.6.2. Performance Standards - Ventilation The Specific Fan Power takes account of

• the efficiency of the fan and • the efficiency of the motor driving the fan. • the pressure drop through the entire ventilation

system.

It is calculated by taking the motor input power (in Watts) and dividing by the fan flow rate (in litres/sec)

A typical target is to achieve 2.5 - 3 W/l/s specific fan power (that is 3 Watts of electrical power supplied to the fan motor to move each litre/second of air through the building).

8.7. Refrigeration and Cooling Equipment For an energy efficient cooling system, consideration is

needed of:

o Efficient equipment. o Thermal storage if appropriate. o Variable speed pumping systems o Variable refrigerant volume systems. o High efficiency motors for fans and pumps. o Insulation of pipes. o Optimised zoning and controls o metering of electrical consumption of chillers and

pumps

8.7.1. Cooling Towers/Water Cooled Chillers

Fig 8.10 Cooling Tower diagram


For large buildings, cooling towers offer much more efficient cooling than standard air-cooled chillers. However, the water quality must be very carefully controlled to minimise the risk of legionella and other bacteria.

In a cooling tower, warm water is sprayed from the top of

the tower typically over a metal honeycomb, with air blown upwards to cool the water. The cool water is collected in a pond at the bottom of the unit. Typically cooling tower might cool water from 35°C to 20°C. The cooling towers are then linked to water cooled chillers which provide chilled water at 6°C or as required.

Regular maintenance and water treatment is essential to

minimise the risk of legionella infections. Typical COP is 6-8.

8.7.2. Absorption Chillers Most absorption chillers use a material lithium bromide

which produces a cooling effect when water is absorbed into it. Heat is required to regenerate the absorber.

Typically absorption chillers are most effective where there

is a source of waste heat in the form of very high temperature water or steam (>100°C). Even then, the machines can be unreliable and unable to cope with varying chilled water demands.

Typical COP is 0.7, so the chillers are usually only a good

solution if a low cost source of heat is available.

There are examples of solar powered absorption chillers in

use, though they are not common, due to the high temperatures required to operate the absorption chillers efficiently. Some chillers are claimed to work with water temperatures as low as 80-95°C, which potentially makes them viable for use with evacuated tube solar heaters, but there are as yet few examples of such installations.

8.7.3. Air Cooled Chillers The most common form of chillers are air cooled. Typical

COPs are in the range 3-5. Refrigerant R22 should not be used since this is an HCFC which damages the ozone layer. Alternatives such as R134a and R410a are now commonly used which, while less damaging to the ozone layer than R22, still have a significant global warming potential if released into the atmosphere.

Designing a system to operate at higher chilled water

temperatures (such as 8°C flow 14°C return) significantly reduces energy use since the chillers operate with a higher COP.

8.7.4. Thermal Storage Ice or phase change materials (PCM) can be used to store

coolth and reduce the size of installed equipment. They also allow the chillers to be run more efficiently at night, when outside temperatures are lower and cheaper electricity may be available. However, due to losses from the storage vessel, they have limited effect on the overall energy use of a building.


8.7.5. Performance Standards - Cooling The energy efficiency of cooling systems is measured

either by the Coefficient of Performance (COP), the Energy Efficiency Ratio (EER) or the Seasonal Energy Efficiency Ratio (SEER). All these measure the useful energy output (heating or cooling), in relation to the energy input (usually electrical power but sometimes heat).

Many standards for energy efficiency specify minimum

requirements for COP for different conditions. Table 8.1 gives the recommended minimum efficiency of

various cooling systems:

Type Size category (cooling capacity) [kW]

Minimum Efficiency [COP]

Air cooled split unit (Cooling mode)

<19 >19, <40 >40, <70

2.93 2.9 2.66

Air cooled split unit (Heating mode)

<19 >19, <40 >40

1.99 3.2 3.1

Table 8.1. Minimum Efficiency Requirements for Unitary Applied Heat Pumps. (ASHRAE Standard 90.1-2001)

8.8. Heating Equipment When a building has a substantial heating demand (e.g. a

hospital) this should not be provided using electricity. That is because the majority of electricity supplied to Botswana is generated from coal, and it takes typically 2.7kWh of coal to generate and transmit 1kWh of electricity. It is

therefore more efficient to generate heat locally using fuel sourced locally. The ideal would be to use unwanted materials (refuse, agricultural waste) or renewable fuels (biogas, wood) which are produced and managed sustainably. However, even using fossil fuels such as coal and oil is more efficient than using electricity.

8.9. Controls The simplest form of control would be a thermostat for

each zone plus a timeclock to allow the plant to be switched on and off at a given time each day. At the other extreme is a complex BMS (building management system) which offers much more flexibility and potential for optimising plant usage and facilities for off-site monitoring/control etc.

However, complex controls only save energy if they are set

up correctly. If the user does not understand how to use them or they are not reset, then the systems may end up using more energy. BMS systems should therefore only be used when it is clear that the building occupant will have the necessary resources to operate them.

Significant savings can be achieved using dead band

control strategies, where the temperature is allowed to drift within a defined band with ventilation only, and no heating or cooling taking place. During the time when temperatures are within the dead band range, all equipment such as chillers, boilers and pumps are turned off. In one case where this was implemented as a retrofit, it resulted in savings of 48% in energy consumption. (Hunn, B.D. p.471). Poor controls will lead to the risk of pieces of


equipment “fighting” (eg one zone heating, one cooling), poor balancing etc.

The degree of user control of the systems is important.

While it is desirable for the occupants of each room to have control over their environment, this can also lead to wasted energy. If the occupants of one room set their thermostat in heating mode and the adjoining room is set in cooling mode, the two units may be busy pumping heat from one to the other, with very little success in achieving the desired temperatures, but considerable expense of energy. It may be better to consider other means of amending the local climate to suit individual preference, such as ceiling or desk fans to reduce, or radiant heaters to increase perceived temperature. These will have little or no affect on dry bulb temperature, but considerable effect on comfort.

8.10. Commissioning & Handover Having designed a highly energy efficient system, it is

important to ensure that it is installed and commissioned so that it functions as intended. The commissioning process is very often rushed and not properly completed because the contractor is eager to finish the job and the client eager to occupy the building. To avoid this, the commissioning process should be carefully programmed and the risks of early occupation explained to the client.

The commissioning process includes cleaning and flushing

of pipework, establishing the correct water treatment, balancing the systems and then verifying that the controls are operating as intended. It is well described in the BSRIA series of documents.

An operation and maintenance manual should also be

prepared including the installation drawings and information on the equipment, spare parts etc. The manual should be arranged with relevant sections addressed to the owner, the building users and the maintenance team.

Structured training in the operation of the systems should

be given to the client, and the client should be encouraged to employ competent maintenance personnel who understand the basic tasks involved (see Section 10, Operation and Maintenance & Building Management Systems).

8.11. Maintenance & Replacement When the building and the mechanical systems are being

designed, consideration must be made for maintenance access and for how plant will be replaced in the future. For plant located on roofs, safe access to the roof for personnel carrying tools should be provided, and balustrades should be considered to reduce the risks of falling.

The mechanical systems selected must be suitable to the

maintainance capacity of the available local tradesmen. This means that a solution appropriate to Gaborone may not be suitable for a remote site in say Bobonong.


8.12. Resource material

8.12.1. Books and papers Davis Energy Group. March 2004 “Development of an improved

two-stage evaporative cooling system”. Prepared for California Energy Commission, Public Interest Energy Research Program . Contract P500-04-016. http://www.energy.ca.gov/reports/2004-04-07_500-04-016.PDF

e-News. Issue 57. December 2006. “Designing Office Buildings to

Perform Better Than Title 24. http://www.energydesignresources.com/resource/224/ Hunn, B.D. (ed) 1996. “Fundamentals of Building Energy

Dynamics.” Massachusetts Institute of Technology.

8.12.2. Codes and Standards. ASHRAE Standard 62.1-2004 – Ventilation for Acceptable Indoor

Air Quality (ANSI Approved) ASHRAE Standard 90.1-2004 - Energy Standard for Buildings

Except Low-Rise Residential Buildings, SI Edition (ANSI Approved; IESNA Co-sponsored)

ASHRAE HVAC Systems and Equipment 2004 ASHRAE HVAC Applications 2003 BSRIA Application Guides - Commissioning of Water Systems in

Buildings

CEN Standard: “Ventilation for Buildings. Design Criteria for the

indoor environment. CEN/CR 1752: 1998-12; CEN; Bruxelles 1998

CIBSE Guide A (Environmental Design) 2006 CIBSE Guide B (Heating, Ventilation, Air Conditioning and

Refrigeration) 2005 CIBSE Guide F (Energy Efficiency in Buildings) 2004 CIBSE Applications Manual 10 - Natural ventilation in non

domestic buildings 2005 CIBSE Commissioning Codes

8.12.3. Websites. Air Conditioning and Refrigeration Institute (ARI) http://www.ari.org/ ASHRAE http://www.ashrae.org/ Association of Energy Engineers (AEE) http://www.aeecenter.org/ CIBSE Chartered Institute for Building Services Engineers http://cibse.org/ EDR. Energy Design Resources http://www.energydesignresources.com/

SECTION 9 LIGHTING – artificial and daylight ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES FOR BOTSWANA Revision 1 September 2007

Energy Efficiency Building Design Guidelines for Botswana – Section 9. LIghting Page 3

CONTENTS

9. LIGHTING 5

9.1. Overview 5 9.1.1. Basic principles 5 9.1.2. Artifical light sources 5 9.1.3. Daylight as a light source 5 9.1.4. Light Fittings 5 9.1.5. Light requirements 5 9.1.6. Lighting control 5 9.1.7. Strategies for energy efficient lighting 5 9.1.8. Standards for energy efficient lighting 5

9.2. Basic Principles 6

9.3. Artificial Light Sources 7 9.3.1. Incandescent lamp. 7 9.3.2. Compact fluorescent lamp. 7 9.3.3. Fluorescent tube. 8 9.3.4. Discharge lamps. 8 9.3.5. Light Emitting Diode (LED). 9

9.4. Daylight as a light source 10

9.5. Light Fittings 11

9.6. Light Requirements 13

9.7. Lighting Control 13

9.8. Strategies for Energy Efficient Lighting 14

Energy Efficiency Building Design Guidelines for Botswana – Section 9. LIghting

9.8.1. Define light requirements. 14 9.8.2. Use daylight as much as possible. 14 9.8.3. Select efficient light sources and fittings. 15 9.8.4. Effective design of lighting layouts. 16 9.8.5. Effective control systems. 16

9.9. Standards for Energy Efficient Lighting 17

9.10. Resource Material 18 9.10.1. Books and papers 18 9.10.2. Codes and Standards 18 9.10.3. Websites 18


9. LIGHTING

9.1. Overview This Section addresses the subject of lighting, including

artificial lighting and daylighting. The different topics that are covered are briefly described below.

9.1.1. Basic principles The basic concepts relating to measurement of light and

lighting efficiency are defined and discussed.

9.1.2. Artifical light sources The different sources of artificial light are described, with

some information on their relative efficiency.

9.1.3. Daylight as a light source Characteristics of daylight as a light source are described in

this section, including the advantages and problems that can be associated with use of daylight in buildings.

9.1.4. Light Fittings The fittings into which a light source is installed are

considered, with emphasis on their energy efficiency.

9.1.5. Light requirements The amount of light required for different spaces is

discussed. There are various standards that define light requirements for particular applications, some of which are reviewed.

9.1.6. Lighting control Different approaches to lighting control are discussed, in

relation to their impact on lighting energy efficiency.

9.1.7. Strategies for energy efficient lighting Various strategies for achieving energy efficient lighting

are discussed, and recommendations are made for approaches to lighting design.

9.1.8. Standards for energy efficient lighting Many codes and standards for energy efficient building

include specific targets for the amount of energy that my be consumed for lighting, including limits on installed capacity and actual consumption.


Fig. 9.1 Visible light.

9.2. Basic Principles Visible light is electromagnetic radiation with a wavelength

that is visible to the eye. Light has an intensity that is determined by the amplitude

of the radiation, and determines the perception of the brightness of the light. It also has a wavelength or frequency that determines the colour. Light may include a range of different frequencies or colour, and sunlight includes the full spectrum of visible light (as well as frequencies beyond the sensitivity of the eye, known as ultra violet and infrared).

The intensity of light (or luminous flux) is measured in

lumen (lm). This is the unit used to measure the amount of light emitted by a light source.

Illuminance is a measure of the intensity of light falling on

a surface. It is measured in lux (lx) that has units of lumen per meter squared (lm/m2). This is the unit commonly used

to specify the level of lighting required on a surface for different activities.

The efficiency with which a light source converts electrical

energy into light is know as its luminous efficacy and is measured in units of lm/W, where lm is the luminous flux emitted by the source, and W is the electrical power consumed.

A luminaire is the fitting that a light source is installed in.

The efficiency of a luminaire is know as the luminaire efficiency (or light output ratio), and is the ratio of the luminous flux emitted by the luminaire and the luminous flux of the source or lamp.

As important as the quantity or brightness of light is the

quality. The three main problems that compromise the quality of light are glare, veiling reflections or excessive brightness ratios.

Glare Glare is experienced when a bright light source such as a

lamp, the sun, or the reflection of a light source is in a person’s field of view.

Veiling Reflections Veiling reflections are caused by bright light sources

reflected from a task surface, such as a book. Brightness Ratio When moving from indoors to outdoors on a clear day, one

experiences a very large change in brightness. This is


unpleasant for a short period of time during which it is difficult to see detail. Then the eye adjusts to the new level of brightness and can see well again. The problem occurs when there are surfaces within the same space with large differences in brightness. Brightness ratio is the ratio of the brightest surface to the least bright.

9.3. Artificial Light Sources

9.3.1. Incandescent lamp. Until recently the most common electric light source was

the incandescent lamp. This is still widely used, although its relatively low energy efficiency is leading to its replacement by other more efficient lamps such as the CFL. The connection to a light fitting is either by screw thread or bayonet.

A large variety of shapes, sizes and power is available, as well as different colour ranges. Typical lamps for household use range from about 40 to 100 W, giving a light output of 420 to 1360lm at the typical lamp efficiency of about 12%.

9.3.2. Compact fluorescent lamp. The compact fluorescent lamp (CFL) was designed as a

more efficient replacement for incandescent lamp. It is supplied with the same fixing system (screw or bayonet), and can be used in many light fittings designed for incandescent lamps.

Power ratings of CFLs that can provide approximately the equivalent light output to incandescent lamps are shown in the table below, together with their efficacy ratings.

Power Light Efficacy[W] [lm] [lm/W]

CFL 7 400 57

11 630 5715 900 6020 1200 60

Incandescent

40 420 1160 710 1275 940 13

100 1360 14 Table 9.1 Efficiency of incandescent and CFL lamps.


Fig. 9.2 Lamp types.

9.3.3. Fluorescent tube. Fluorescent tubes are the main form of lighting for offices

and commercial buildings.

They are a form of gas discharge lamp, and are formed in a long thin glass cylinder with contacts at either end that secure them to the fitting (or luminaire) and provide the electrical connection.

The tube contains mercury vapour at low pressure, and the inner wall of the glass is coated with a phosphor that reacts to ultra-violet radiation. When electricity is passed through the vapour it emits UV radiation that is converted by the phosphor to visible light.

The most efficient fluorescent tubes are the T5. With a smaller diameter (16mm) than earlier tubes, these can achieve a luminous efficacy of up to 104lm/W.

9.3.4. Discharge lamps. Discharge lamps work by striking an electrical arc between

two electrodes, causing a filler gas to give off light.

Different metals and filler gasses can be used to provide a range of colour and brightness.

Discharge lamps provide high luminous efficacy combined with long life, resulting in the most economical light source available.


9.3.5. Light Emitting Diode (LED). LEDs use semi-conductors to convert electrical energy directly into light. They are only recently becoming available as a light source for lighting purposes, and are highly efficient and long lasting. LED torches are becoming very popular, as they provide a far longer battery life than other types of light source.

Fig. 9.3 Light emitting diodes.


Fig. 9.4 The spectrum of solar radiation.

9.4. Daylight as a light source Daylight entering a building all originates from solar

radiation, but it may have arrived by a number of different routes, each of which will have modified it in various ways.

Solar radiation when it reaches the earth’s atmosphere covers a wide spectrum of wavelengths, including the range of visible light, ranging ranging from red at the longest wavelengths of about 700 nm to violet at the shortest wavelengths of about 400 nm. This is selectively filtered by the atmosphere, so that the radiation reaching the surface of the earth is less than that above the atmosphere. The daylight entering a building may include direct sunlight when the window has a view of the sun, as well as diffuse sunlight that has been refracted by clouds, and reflected from various surfaces such as clouds, ground or other buildings. Daylight can therefore vary greatly with weather conditions, ranging from total cloud cover to clear sky with direct sunlight. Daylight has the potential to provide large amounts of effectively free energy, reducing the amount of electricity required to achieve a given level of lighting. However day lighting must be designed with care to ensure a high quality of light for the users.


The effectiveness of daylight as a light source is measured as the “Daylight Factor”. This is the average illuminance (lux) inside a room at a standard height above floor level compared to the illuminance outdoors on an overcast day. It is usually stated as a percentage. Typically the daylight factor should be between 2-5%. Less than 2% is experienced as a dim space, whereas over 5% results in unnecessary heat gain. The illuminance of the sky is typically in the range 20,000 to 100,000 in direct sun, and between 5,000 to 20,000 when the sky is overcast. Two potential problems associated with the use of daylight in buildings are glare and heat. Glare occurs when a bright light source such as the sun is in the field of view of users. It can also occur when reflections of the sun are in the field of view. The simplest way to control glare is to avoid large windows on the east and west elevations, and ensure that windows on the north elevation are shaded to control the low winter sun. The south elevation is very seldom exposed to direct sun, and even then it is at an oblique angle that is less of a problem. For windows that are exposed to direct sun at certain times of day and year, this can be controlled by careful design of the geometry of windows and the use of shading devices such as blinds or shutters.

Daylight is always associated with heat, and the challenge is to maximise the benefit from daylight with minimum heat gain. Daylight actually has a far better luminous efficacy than any electrical light source as can be seen in the graph.

Generally daylight entering through windows provides far higher light levels than are actually required, resulting in significant associated heat gains. Typically the heat input from direct solar radiation on a horizontal plane is about 900W/m2, whereas indirect radiation through a window is typically 350W/m2 at midday in summer.

9.5. Light Fittings The fitting into which a light source is installed is an

important consideration in achieving energy efficiency.

The Fittings for fluorescent tubes are called luminaires and come in a variety of types, suitable for different applications.

The important consideration in selecting a fitting is to achieve maximum efficiency without compromising the quality of light. This requires a fitting that transfers as much light as possible from the lamp to the working surfaces, without resulting in direct glare, veiling reflections or excessive brightness ratios.

The important features of a luminaire are the reflector and the lens. Common types of luminaire are described below.


Channel luminaires. This simplest form of luminaire is simply a tube holder

with a white reflector. This has a high efficiency, but can result in glare problems since the lamp is visible.

Prismatic diffuser. This uses an acrylic prismatic diffuser to conceal the lamps,

resulting in low surface brightness, reducing glare problems. It is not very efficient, due to light losses in the diffuser.

Parabolic louvre. This provides excellent glare control without compromising

efficiency, using reflective aluminium louvres to conceal the lamps from low viewing angles.

Uplighter. In this system the lamp is concealed by a reflector that

directs the light onto a curved reflector that in turn directs it down into the room.

Luminaire Typical total light output ratio (% of lamp flux)

Channel 80 – 90

Prismatic diffuser 55

Parabolic louvre 70

Uplighter 60

Table 9.3 Performance characteristics of luminaires (source:

Lascon catalogue)

Channel Parabolic louvre

Diffuser Concealed lamp

Fig. 9.5 Typical luminaires for fluorescent lamps.


Task and examples of applications Illuminance [Lux] Lighting to infrequently used areas Minium service illuminance 20 Interiror walkway and car-park 50 Hotel bedroom 100 LIft interior 100 Corridor, passageways, stairs 100 Escalator, travellator 150 Entrance and exit 100 Staff changing room, cloak room, lavatories, stores 100 Entrance hall, lobbies, waiting room 100 Inquiry desk 300 Gate house 200 Lighting for working interiors Inrequent reading and writing 200 General offices, shops and stores, reading and writing 300 - 400 Drawing office 300 – 400 Restroom 150 Restaurant, cafeteria 200 Kitchen 150 – 300 Lounge 150 Bathroom 150 Toilet 100 Bedroom 100 Classroom, library 300 – 500 Shop, supermarket, department store 200 – 750 Museum and gallery 300 Localised lighting for exacting task Proof reading 500 Exacting drawing 1000 Detailed and precise work 2000

Table 9.4 Recommended average illuminance levels. (Source:

Malaysian Standard MS 1525:2001)

9.6. Light Requirements Indoor light requirements vary depending on the task to be

carried out. Typical lighting requirements for a variety of tasks are given in table 9.4.

In work environments such as offices or schools it is

generally more effective to provide a low level of background lighting, sufficent for orientation and general activities, say 150 - 200lux and local task lighting at each work station as required for the particular activity. This results in savings both on the initial installation cost as well as recurrent expenses compared to providing a sufficient background light level for typical office tasks (300-400lux).

9.7. Lighting Control Control of lights may be manual or automated. Effective

zoning of lights in different circuits is critical to enabling energy efficient behaviour. This should provide enough flexibility to allow for variations in use patterns and availability of daylight.

Sensors including light level sensors and occupancy sensors are available that can be used in automatic control systems and combined with dimmers, on/off switches and time switches to achieve energy savings. Light level sensors combined with dimming controls can automatically reduce levels of artificial light in relation to the availability of daylight.


9.8. Strategies for Energy Efficient Lighting The challenge in lighting design is to provide sufficient

light where it is required at the times when it is required, without providing excess light. If this is done using the most appropriate light sources and fittings, and combined with an effective control system, then substantial energy savings can be achieved.

The key strategies to achieving this are as follows:

o Define light requirements. o Use daylight as much as possible. o Select efficient sources and fittings. o Effective design of lighting layout. o Effective control systems.

9.8.1. Define light requirements. An accounting approach is probably best, establishing a

clear ‘budget’ that specifies the lighting levels required at

different locations at different times. Avoid specifying lighting levels that are higher than actually needed. Providing low background light levels with flexible task lighting at workstations ensures sufficient light where it is actually needed.

Quality of light should also be considered, including

particular requirements regarding glare, brightness ratio, etc.

These requirements should be included in the Design Brief,

and agreed with the client at the pre-design stage of the project.

9.8.2. Use daylight as much as possible. The availability of daylight is greatly affected by the

overall shape and orientation of the building, so this is an important opportunity for coordination between different members of the design team. Generally north and south facing walls offer easier opportunity for daylight without

Fig. 9.6 Examples of lighting control


problems from direct sunlight. The east and west facing walls are subject to direct sunlight in the morning and evening respectively, and windows facing these directions therefore need to be provided with shading devices.

The use of daylight is limited by access to external walls.

Various features can be used to increase the penetration of daylight further into the interior of a building, including light shelves, light pipes, and skylights.

Fig. 9.7 Use of a lightshelf to increase daylight penetration. (Source: Advanced Lighting Guidelines, New Buildings Institute)

Light shelves are usually located near the ceiling, often

above a window to reflect daylight onto the ceiling and back into the interior of the building. The increase in interior light levels using a light shelf is illustrated in Fig. 9.7.

Daylight can also be introduced through the roof with

skylights. Again the challenge is to avoid heat gain and direct sunlight, which can be done with shading devices and careful orientation.

Light pipes can be used to ‘transport’ light from the roof,

through a roof space into the interior of a building. They are basically ducts with highly reflective interior surfaces.

9.8.3. Select efficient light sources and fittings. For most industrial and commercial applications with low

ceiling levels the most effective background lighting will fluorescent tubes. The most efficient are T5 tubes, and the most practical size is 1200mm since these are easy to change and not so vulnerable to breakage as the longer 2400mm tubes. Indirect fittings should be considered where possible, since they provide a more even lighting level (lower luminance ration) and therefore allow for lower absolute light levels than direct fittings.

For localised task lighting and most residential

applications, CFL lamps are most appropriate. They should not be undersized, and it is recommended to use a ratio of 3:1, when replacing incandescent bulbs, rather than the more optimistic 4:1 ratio often claimed. (i.e. a 75W incandescent bulb can be replaced with a 25W CFL). (EDR Design Brief: Lighting).

High Intensity Discharge lamps, such as Metal Halide

lamps should be used in situations where high intensity point sources of light are required, typically in high ceiling


industrial or commercial applications and for outdoor lighting.

9.8.4. Effective design of lighting layouts. The number and location of light fittings is important to

ensure that the required light levels are achieved with a minimum of fittings. The use of formulae and diagrams has largely been replaced with software packages that are available, many for free, that allow modelling of different lighting arrangements.

9.8.5. Effective control systems. Having achieved an efficient lighting layout, it will only achieve energy efficiency in practice if the lights are effectively controlled, such that they are turned on only when actually required, and off at all other times. This requires appropriate zoning, whereby the lights that are required at different times are on separate switching circuits. Typically this may result in two or three zones in a room, based on distance from windows. Areas furthest from windows may require lights to be on at all times of occupation. Areas closer to the windows can use daylight for much of the daytime. Zoning should also relate to occupancy patterns, so that if only one two people are working they have the opportunity to turn on only those lights that are needed.

The choice between manual or automatic control of lights is critical. People tend to switch lights on when there is insufficient light for the task they are doing, but not switch

Fig. 9.8 Energy savings from use of dimmers controlled by light sensors. (Florida Solar Energy Center).

them off when they are no longer required. It is therefore often best to design the system such that the occupants turn lights on, and they turn off automatically.

Using light level sensors in combination with dimmers to maximise the use of daylight can result in large energy savings as illustrated in the following diagram.


In this case an office space with south-facing windows had a control system that used electronic dimming ballasts to control the lights in response to available daylight resulting in a saving of 38%. (EDR Design Guide: Lighting).

9.9. Standards for Energy Efficient Lighting A large number of lighting codes and standards are

available in different countries. These aim to control the amount of energy consumed for lighting by setting limits on the installed lighting capacity for different purposes. They may also have requirements for switching and control to ensure that the building operators have the ability to control lighting efficiently.

The requirements of some typical lighting standards are

given in the table below:

Lighting energy (W/m2) by building type Standard Office Retail Hotel School ASHRAE 90.1-2001

14 20 18 16

Malaysian Standard 1525-2001

20 20-30 17-20 18-25



9.10.1. Books and papers EDR. Design Brief: Lighting. Energy Design Resources. Lascon. Comprehensive Catalogue, 1998/99. Lechner, N. 1990. Heating, Cooling, Lighting – Design Methods for

Architects. USA. John Wiley & Sons. Benya, J., et. al. “Advanced Lighting Guidelines” 2003. New

Buildings Institute. http://www.newbuildings.org/lighting.htm.

9.10.2. Codes and Standards ASHRAE Standard 90.1-2001. Energy Standard for Buildings

except Low Rise Residential Buildings. Malaysian Standard MS1525: 2001. Code of Practice on Energy

Efficiency and Use of Renewable Energy for Non-Residential Buildings. Department of Standards, Malaysia.

9.10.3. Websites EDR. Energy Design Resources . http://www.energydesignresources.com/ EERE Building Technologies Program Home Page http://www.eere.energy.gov/buildings/ New Buildings Institute http://www.newbuildings.org/

WBDG - Whole Building Design Guide http://www.wbdg.org/ The Lighting Association http://www.lightingassociation.com/ CLEAR http://www.learn.londonmet.ac.uk/packages/clear/index.ht

ml

SECTION 10 OPERATION & MAINTENANCE AND BUILDING MANAGEMENT SYSTEMS ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES FOR BOTSWANA Revision 0 July 2007

Energy Efficiency Building Design Guidelines for Botswana – Section 10. Operation & Maintenance, and BMS Page 3

CONTENTS

10. OPERATION & MAINTENANCE 4

10.1. Overview 4 10.1.1. Design for Operation and Maintenance. 4 10.1.2. Operation and Maintenance Manual. 4 10.1.3. Building Management Systems 4

10.2. Design for Operation & Maintenance 4 10.2.1. Facility Management. 4 10.2.2. Resilience. 4 10.2.3. Recommendations. 5

10.3. Operation & Maintenance Manual 5 10.3.1. Typical format for an O & M Manual 6

10.4. Building Management Systems 7

10.5. Resource Material 8 10.5.1. Books and papers 8 10.5.2. Websites 8

Energy Efficiency Building Design Guidelines for Botswana – Section 10. Operation & Maintenance, and BMS

10. OPERATION & MAINTENANCE

10.1. Overview This Section addresses the subject of operation and

maintenance. The different topics that are covered are briefly described below.

10.1.1. Design for Operation and Maintenance. It is important that a building is designed with the

capability and resources of the users and operators in mind to ensure that it is able to function as intended. Different approaches to operation and maintenance are considered.

10.1.2. Operation and Maintenance Manual. The Operation and Maintenance Manual is an important

tool in ensuring the effective and energy efficient functioning of the building. A basic outline of such a document is suggested.

10.1.3. Building Management Systems Building Management Systems are briefly described, and

the conditions under which they are appropriate are considered.

10.2. Design for Operation & Maintenance

10.2.1. Facility Management. In Botswana until recently there was little awareness of the

importance of building operation. Even large and complex buildings in many cases do not have a dedicated ‘Facilities Manager’ or similar employee who is responsible for the

operation and management of the building. As a result, control of air conditioning equipment, lighting, etc is largely left to the individual occupants who generally are not given any training in how to achieve the best performance from the building at minimum cost.

Designing a building with the control systems that can

achieve high levels of energy efficiency is pointless if these are not managed to achieve this. It is therefore essential that the building owners understand the human resource structure that will be required to operate and maintain the building, and commit to implementing this in coordination with the building commissioning and handover process.

10.2.2. Resilience. Maintenance requirements may vary greatly depending on

the materials, components and systems that are included in the building. The implications of departures from the ideal maintenance programme may also vary, depending on the resilience of the different elements of the building.

Fig. 1 Modern building in Gaborone, highly

dependant on mechanical cooling.


For example, a highly insulated ‘active’ type of building

may become uninhabitable in a very short time if the air conditioning system breaks down. It will therefore require backup power supplies, redundancy in the mechanical equipment and efficient planned maintenance procedures to ensure that the backup kicks in when a fault occurs. In contrast, a climate sensitive building that has a high level of interaction with its surroundings may be more resilient, and merely become less comfortable, but still habitable while breakdowns are being repaired.

Generally there is a strong correlation between effective

maintenance and energy efficiency. Poor maintenance of equipment tends to result in lower efficiency, and hence higher cost in relation to performance. In some cases poor maintenance may reduce actual operating cost, but always at the expense of environmental quality. Large numbers of blown fluorescent tubes or air conditioners that are dysfunctional may save money, but at the expense of poor lighting levels, or uncomfortable rooms, which will result in poor productivity and employee morale.

10.2.3. Recommendations. o Discuss operation and maintenance requirements

during client briefing meetings, and include these in the design brief.

o Prepare outline operation and maintenance manual at an early stage, and include information as design and construction proceed.

o Discuss O&M implications with client as design and construction proceed, to ensure that these are understood and accepted.

10.3. Operation & Maintenance Manual On larger projects it is becoming common for the building

design team to be required to prepare an Operation and Maintenance Manual to be handed over to the client on commissioning of the project.

This is an opportunity to ensure that the energy saving

concepts that have been designed into the building are formally communicated to the owner and hence to the users of the building.

Ideally the outline of the O&M manual should be prepared

at an early stage of the design, and updated as the project develops. In this way, the team will ensure that O&M considerations are addressed at each stage of the design.

The contents of the O&M manual will vary between

different projects, depending on the systems that are included in the buildings.


10.3.1. Typical format for an O & M Manual A typical format would be as follows:

1. GENERAL INFORMATION 1.1. Building Location, Ownership and Tenancy 1.2. Building Physical Data 1.3. Building Construction History 1.4. Utility Providers 1.5. Other Important Contacts 2. O&M OBJECTIVES AND GOALS 2.1. O&M Objectives 2.2. O&M Goals 3. O&M MANAGEMENT 3.1. Organisational chart 3.2. Job descriptions 3.3. External Contracts 4. BUILDING SYSTEMS 4.1. Building Structure 4.2. Building Envelope 4.3. External works and landscaping 4.4. Internal Finishes 4.5. HVAC system 4.6. Electrical system 4.7. Telecommunications 4.8. Water 4.9. Waste water

5. ACTIVITY SCHEDULES 5.1. Operational Task Schedule 5.2. Maintenance Task Schedule 6. O&M PERFORMANCE MEASUREMENT 6.1. Indicators 6.2. Baseline data 7. O&M PROCEDURES AND REPORTING 7.1. Timesheets 7.2. Equipment File 7.3. Activity Schedules 7.4. Work Order File 7.5. Indicator Data File 7.6. Quality Assurance 8. O&M PLANNING AND REVIEW 8.1. Annual plan 8.2. Annual budget 8.3. Monitoring and review APPENDICES All relevant documents including title deeds,

insurance, drawings, schedules manuals, contracts, etc.


10.4. Maintenance Maintenance is the client's responsibility, but all too often

clients employ poorly qualified staff and only attend to equipment when it stops working. Preventive maintenance consists of weekly and monthly checks on equipment, and early replacement of filters, fan belts etc when they show signs of wear. Fans operating with dirty, partially blocked filters will use more energy and not achieve their design ventilation rates.

In any chilled water or LTHW system, it is essential that

the water quality is maintained and that the correct chemical dosing is used. Poor water treatment will drastically reduce the life of the equipment. Checks should also include spotting any water leaks from pipes or equipment. If leaks are not repaired immediately they can lead to damage of the building fabric as well as highly accelerated corrosion due to increased oxygen levels in the pipework systems. In any system with open cooling towers, good maintenance is essential to avoid the risk of Legionella virus and other problems developing.

Good preventive maintenance can both increase the lifetime

of equipment and also improve its efficiency thus reducing energy use.

10.5. Building Management Systems Building Management Systems are electronic controllers

linked together via a computer network which are used to control important pieces of plant such as air handling units,

chillers, pumps and so on. Variables such as set point control temperatures and hours of operation can be adjusted using software, and the controllers can also be programmed to achieve very sophisticated levels of control such as turning plant on at night when external temperatures are suitable for night cooling.

Typically they are installed in large buildings over about

10,000m2. While they are principally used to control HVAC equipment, but may also operate lighting, fire control and security systems.

BMS has the potential to provide energy savings of up to

about 10% if it is effectively implemented. However many systems have been found to be under performing, resulting in lower energy savings or no savings at all. (EDR Design Brief: Energy Management Systems).

For a BMS to be effective it is essential that it is designed

to suit the requirements of the building, correctly installed and commissioned and regularly maintained to ensure that it functions as intended.

BMS has the potential to achieve substantial energy

savings. It should however only be considered if the resources are available to design, install, commission, operate and maintain the system.


Fig 10.2 BMS system


10.6.1. Books and papers EDR. Design Brief: Energy Management Systems. Energy Design

Resources. http://www.energydesignresources.com/resource/18/ EECOB Project, Dept. of Energy, Botswana. Nov. 2005. ‘Guidance

on Developing Building O&M Manuals Part II’. Lechner, N. 1990. ‘Heating, Cooling, Lighting – Design Methods

for Architects’. USA. John Wiley & Sons.

10.6.2. Websites ASHRAE American Society of Heating, Refrigerating and Air-

conditioning Engineers. http://www.ashrae.org/ CIBSE Chartered Institute for Building Services Engineers http://cibse.org WBDG - Whole Building Design Guide http://www.wbdg.org/

SECTION 11 SIMULATION ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES FOR BOTSWANA Revision 1 September 2007

25 Fri2002

26 Sat 27 Sun 28 Mon 29 Tue 30 Wed 31 ThuTi /D t


CONTENTS

11. SIMULATION 5

11.1. Summary 5

11.2. Overview 5 11.2.1. Definition. 5 11.2.2. History. 5 11.2.3. Opportunities 5 11.2.4. Limitations 6

11.3. Simulation Tools 7

11.4. Elements of Simulation 12 11.4.1. Weather and location data. 12 11.4.2. Building construction data. 14 11.4.3. Occupancy and equipment. 15

11.5. Simulations. 16 11.5.1. Output reports. 17 11.5.2. Analysis. 17

11.6. Design Stages 17 11.6.1. Scheme Design 18 11.6.2. Detailed Design 19

11.7. Building Performance Simulation 20 11.7.1. Compliance with Codes and Standards. 20

11.8. Resource Material 21 11.8.1. Books and papers 21

Energy Efficiency Building Design Guidelines for Botswana – Section 11. Simulation

11.8.2. Codes and Standards 21 11.8.3. Websites 21

Energy Efficiency Building Design Guidelines for Botswana – Section 11. Simulation Page 5

11. SIMULATION

11.1. Summary This Section gives an overview of the role of simulation in

the building design process. The opportunities that simulation offers and its limitations are considered.

A number of available software packages are compared in a

table that provides basic information on the features, capabilities and cost of each, as well as the links to further information.

The elements of simulation are described, indicating the

information that is needed regarding climate, location and the building itself.

The role of modelling in different stages of the building

design process is then considered in more detail.

11.2. Overview

11.2.1. Definition. Simulation is defined in this context as the use of computer

software tools to predict the performance of buildings, particularly with respect to indoor environment, energy transfer and lighting.

11.2.2. History. Software tools for building simulation have been available

for about the last 30 years, but much development has taken place in the past 10 years making such tools more easily available and user friendly. The main constraints in the use of simulation have been the availability and cost of the software, availability of detailed weather data, and even more so, the skills and time required to use these.

11.2.3. Opportunities There is a wealth of information available on how to design

energy efficient buildings for different climates. This includes suggestions for orientation of buildings, use of shading devices, placement of insulation and thermal mass, and appropriate use of ventilation. Many architects and engineers are aware of these concepts and apply them to the buildings that they design. It is however only with the use of computer simulation tools that the actual quantitative impact of different approaches can be determined with useful accuracy. Especially interactions between different building systems and the feed-backs involved can be analysed, which is generally not possible without an


advanced simulation software except in a very simplified form.

It ‘makes sense’ that a building should be orientated to

present the smallest elevations to the rising and setting sun, but what is the actual effect on internal temperature or energy consumption of a different orientation? How sensitive is the relationship? What is the effect on performance of a shift in orientation of say 10, 20 or 30 degrees from the optimum?

It ‘makes sense’ to control heat transfer through the roof by

fitting insulation and having a light coloured roof surface, but how much insulation is economically efficient? How much difference does the roof colour make?

For buildings at the design stage, questions such as these

can only be reliably answered by carrying out simulations that provide actual quantitative information on the dynamic behaviour of the proposed design.

The use of simulation in the building design process allows

the design team to quantify the actual impact of such design decisions, so that rational decisions leading to the most cost effective approach can be made based on actual quantitative information. A key advantage is that through the use of advanced simulation software such information becomes available much earlier in the design process than would otherwise be possible thereby providing many opportunities for improving thermal performance in as cost effective a manner as possible.

The usefulness of energy simulation is greatly enhanced when it is combined with lifecycle cost analysis (See Section 12, Life-Cycle Cost Analysis). The combination of these two modelling tools enables rational choices to be made regarding measures that impact on energy performance in the context of the total cost of a building over long periods of time, even over its entire expected life to demolition.

11.2.4. Limitations Naturally the benefits of simulation come at a cost. The

software itself can be quite expensive, depending on the package that is selected. The greater cost however is the time and skill required to set up the simulation and run the various scenarios to provide the required information.

The more accurate and detailed the model, the more time is

needed to prepare it, so it is important to determine the minimum amount of detail required to provide the information that is relevant at each stage of the design process.

In practice the economics of building simulation need to be

considered in determining the extent to which it is appropriate to apply it in the design methodology. There are substantial economies of scale, such that a large building is not proportionally more time consuming to model than a small building, and there is therefore more opportunity to use simulation for large projects. Large projects in general also have more to gain from simulations since the increased size brings with it increased complexity as well. Therefore accuracy of simplified methods quickly


deteriorates with increasing size and complexity of buildings.

Much information may be obtained from simulation of

typical ‘generic’ building types in a particular climate. This information can then be applied to a large number of individual buildings that are essentially similar to the generic building. An exercise to model a number of ‘generic’ building types in the Botswana climate has been carried out under the Energy Efficiency and Energy Conservation in the Building Sector project. The results of this are available in the report: ‘Parametric simulation of the energy performance of three generic building types in Gaborone, Botswana’. Department of Energy, Government of Botswana, January 2007.

11.3. Simulation Tools A large number of software packages are available for simulating buildings. They differ widely in complexity and ease of user interface. A report prepared in July 2005 (Crawley et. al.) provides a comparison of 20 building energy simulation programs including an assessment of their capabilities. The authors recommend that it may be most efficient to use a suite of different programs for different stages of the design process. The report contains 14 tables detailing the specific features and capabilities of the programs. The comparison of 17 programs in Table 11.1 is largely based on information from this report.

It can be seen from the table that there is considerable variety in the available software, in terms of their features, performance and price. Price is not necessarily an indicator of capability or quality, and some of the most comprehensive and powerful software is available free (e.g. EnergyPlus, which however has a very cumbersome user interface.)


Software package

URL Features

HVAC modelling

Interface Price (P)

BSim www.bsim.dk Advanced dynamic Thermal simulation. Includes moisture analysis, Daylight analysis, natural ventilation, contribution from building integrated PV systems, advanced simulation of shades and solar illumination in and around the building etc.

Various / Complex

Accepts DXF input. Produces output files compatible with Excel. Can export data to various specialized programs like Radiance and CFD software. User friendly graphic interface. Can generate the necessary climate input files from user-provided data (e.g. measured hourly data) using very flexible input criteria

EUR2,680 P20,500 Plus annual support subscription fee of approx. P 4500

DesignBuilder www.designbuilder.co.uk

Provides a graphic input and output interface for EnergyPlus

Various Graphical input for building model. Graph / table output formats.

US$1,449 P8,830

ECOTECT www.ecotect.com Highly visual and interactive. Comprehensive scripting engine.

Simple Can export to specialised programs e.g. Radiance, EnergyPlus, etc.

US$690 P4,200

Ener-Win members.cox.net/enerwin/

Energy consumption analysis. Peak loads. Daylighting analysis. Life-cycle costing.

Simple US$49.00 P300


Software package

URL Features

HVAC modelling

Interface Price (P)

Energy Express www.ee.hearne.com.au Design tool for evaluating energy efficiency of commercial buildings. Separate packages for architects and engineers.

Simple / Complex

Fast and accurate input.

AUD$945 P4,223

Energy-10 www.nrel.gov/buildings/energy10

Intended for early stages of design of residential and small commercial buildings. Full life-cycle costing.

Simple Fast, user-friendly input. Built-in graphs illustrate different strategies.

US$325.00 P1,980

EnergyPlus www.energyplus.gov Primarily a simulation engine. Integrated simulation for temperature, comfort and loads. Moisture analysis. Complex modelling of HVAC systems and controls.

Complex Text file input and output files. Suitable for use with purpose made interface programs, e.g. DesignBuilder.

free

eQUEST www.doe2.com/equest Easy to use. Energy cost estimating. Daylighting and lighting system control. Energy efficient measures.

Simple

Interactive input interface. Output graphs to compare alternatives. 3D view of building geometry. HVAC system diagrams.

free

ESP-r www.esru.strath.ac.uk/Programs/ESP-r.htm

Models thermal performance, air flow, HVAC systems and electrical power flow.

Complex Can increase model complexity as a project develops. Works with third party tools such as Radiance.

free


Software package

URL Features

HVAC modelling

Interface Price (P)

HAP www.commercial.carrier.com

Simulates building energy performance to derive annual energy use. Used for sizing and design of HVAC system.

Complex GUI input. Graphical and tabular reports. Comparative reports for alternative schemes.

?

HEED www.aud.ucla.edu/heed

Single zone simulation program for use at the beginning of the design process. Energy cost analysis.

Simple User friendly GUI input interface. Graphical output reports comparing alternative schemes.

Free

IDA ICE www.equa.se/ice Based on a general simulation platform. Can model displacement ventilation, active chilled beams, radiative devices, air and water based slab systems.

Complex Four levels of interface, from simple, wizard to programmer.

SEK18,000 P15,000

IES<VE> www.iesve.com Dynamic thermal simulation tool. Can link to MacroFlo for ventilation and infiltration analysis. Links to SunCast for shading and solar penetration analysis. Part of a suite of programs covering many aspects of building design.

Complex Results viewed in Vista, a graphics tool for presentation and analysis.

?


Software package

URL Features

HVAC modelling

Interface Price (P)

SUNREL www.nrel.gov/buildings/sunrel

Models small buildings dominated by envelope loads, including natural ventilation and infiltration.

Simple Graphical interface may be used to create input files.

US$50 P305

Tas www.edsl.net A suite of programs that simulate thermal performance of buildings and their systems. Models natural and forced airflow.

Complex Wizards for creating models. Graphical results reporting with multi-run comparisons.

?

TRACE 700 www.tranecds.com Models building and HVAC systems in four phases: design, system, equipment, economics. Specifically intended for optimisation of the HVAC system.

Complex Wizards for creating models. Graphical results reporting with multi-run comparisons.

?

TRNSYS sel.me.wisc.edu/trnsys A modular transient system simulation program adapted to model building thermal performance, HVAC system performance. Easily adapted to develop special purpose applications.

Complex Visual interface for data input. Full source code provided for components and simulation engine.

US$4200 P25,600

Table 11.1. Camparison of energy simulation software


11.4. Elements of Simulation

11.4.1. Weather and location data. A key requirement for accurate simulation of energy

performance or lighting in buildings is comprehensive and relevant data for the weather conditions.

Weather data is often compiled into a database that includes

hourly data for various parameters for a typical meteorological year. A standard format and methodology for the preparation of such a database has been adopted by most developers and is called TMY2 (Typical Meteorological Year 2). To prepare a TMY2 file for a particular location, hourly data for as many years as possible must be collated, and analysed to determine the averages for each month. The most representative full month’s data for each month of the year is then selected, and used to build up a ‘year’ of hourly data. The first and last days of each month are then modified to smooth the transitions from one month to the next. In this way the different data parameters are kept together for each hour, and realistic variation within each month is maintained.

TMY2 files are readily available for many locations around

the world, but unfortunately not many in Southern Africa, and none in Botswana. The EECOB project has developed a weather files for Gaborone and Maun for use with EnergyPlus and DesignBuilder. Weather files for other locations in Botswana will also need to be developed due to the variation in climate across the country (see Section 3, Climate).

Different software packages use different weather file

formats, but most include a translation package to enable a TMY2 file to be translated into the required format.

The weather data required by a particular package depends

on the approach taken in modelling different heat flow and lighting processes. Typically they will include the following:

• Dry bulb air temperature. • Wet bulb air temperature. • Relative humidity. • Atmospheric pressure. • Wind speed. • Wind direction. • Direct normal radiation. • Diffuse horizontal radiation. • Horizontal infrared radiation.

The location is defined by the longitude and latitude as well

as the elevation above sea level. Other information that may be required includes ground

temperatures at various depths.


Fig. 11.1. Hourly average temperature and Relative

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11.4.2. Building construction data. The building needs to be defined, both in terms of the

envelope geometry and the types of materials. The input interface for this information is an important

consideration in selecting a simulation programme. At one extreme is a programme like EnergyPlus, which is

entirely based on text input. Each vertex of each surface of the building needs to be defined by its Cartesian coordinates, which is a time consuming and tedious process.

Other programmes provide graphical tools to input the

geometry, similar to simple CAD tools, while some allow the basic geometry to be imported as a DXF file from a CAD programme such as AutoCad.

The definition of the materials is generally supported by

libraries of standard components and combinations of components, which may be edited by the user.

Fig 11.2 Building construction (DesignBuilder)


11.4.3. Occupancy and equipment. The occupancy of the building and the equipment to be

operated need to be specified, including the times of occupation and use of equipment. These are typically specified with schedules to define the times of occupancy and starting and stopping times for equipment use. The power consumption and efficiency of equipment needs to be defined to determine the heat output. (See Fig. 11.2.)

The equipment definition may also include specification of

HVAC equipment, depending on the purpose for which the simulation is being carried out. Initial simulations to test out different envelope options may be carried out without any HVAC equipment specification, and report either on the ‘floating’ room temperatures, or define the heating and cooling energy needed to achieve defined indoor environment conditions.

Lighting equipment must also be defined. Again there is

often the choice to define actual lighting layouts, and allow the programme to calculate the loads, or to define target light levels and have the programme determine the lighting loads to achieve these. In this case the contribution of daylighting through windows and other openings may also be determined by the programme if this facility is provided.

Fig. 11.3 Typical input data (DesignBuilder)


Fig. 11.4. Typical output from simulation (DesignBuilder).

11.5. Simulations. Having input all the required information relating to the

climate, location, building, occupation and equipment, the simulation runs may be performed. Typically a number of simulations will be run for each of several scenarios to try out the effect of changing one or more parameters.

The different simulations in each case may include

different climatic conditions, e.g. typical summer and winter weeks, and a full year, depending on the purpose of the simulation. The sizing of HVAC equipment requires a simulation of the most extreme conditions under which the required indoor climate conditions are to be fulfilled.

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11.5.1. Output reports. Output reports may be in the form of text files that can then

be imported into a spreadsheet programme for further processing(as with EnergyPlus), or the programme itself may generate both tabular and graphic output reports.

It is critical to consider what information is relevant at any

particular stage of the design process, and how to use it to best advantage. This will be considered in further detail in subsequent sections of this paper.

11.5.2. Analysis. The results of the simulations may be analysed in a number

of ways, depending on the purpose of the simulation. Typically the selected indicators may be plotted on a graph

for various simulations to illustrate the effect of changing various parameters.

In other cases it may be more appropriate to present the

results in a table format, e.g. where further calculations are to be performed using the results.

11.6. Design Stages Simulation may be used as a tool at various stages of the design process. At each stage, the objectives, methods and analysis will be different. The design stages are discussed in more detail in Section 5. Design and Construction Process.

Fig. 11.5. Cost / benefit of design change with regard to

energy savings. (Source: ENSAR Group)


11.6.1. Scheme Design The scheme design stage is the stage at which there are the greatest opportunities coordinate and integrate the design of the different building systems to achieve the energy efficiency targets and criteria that were defined in the Design Brief. At this stage it is relatively easy and cheap to make substantial changes in the design approach, before the detailed design has been carried out. Building Simulation can be an effective tool in achieving this, since it allows the design team to try out a number of initial concepts and evaluate their performance under the climatic conditions of the proposed site.

11.6.1.1. Model preparation. For this purpose the model should not require a lot of detail, since it is the general concepts that are being evaluated. Suitable software packages for this purpose should provide a fast and easy input interface, so that various approaches can be modelled without taking too much time. Typically the software may automatically generate windows to a specified ratio of wall area for each elevation. Lighting may be specified in terms of the required lux levels, and air conditioning systems by indicating the set points and the times when these are required to be achieved.

11.6.1.2. Simulations and results. The objectives of simulation at this stage are to compare

the effectiveness of different design approaches, and in particular the interaction of different building systems.

A decision therefore needs to be made as to what the most

appropriate indicators for success will be. This may vary for different building types.

For buildings that are unlikely to use mechanical cooling or

heating, the indicator may be ‘comfort temperature’ (weighted average between radiant temperature and dry bulb temperature). If heaters are likely to be used in winter, it may be appropriate to use heating energy as the indicator in winter.

For buildings that will be fitted with HVAC systems,

annual energy use may be used as an overall indicator. However other indicators may be needed to determine the effectiveness of particular building elements. Typical summer and winter week results will indicate whether the building functions well under each of these conditions.

In all cases it is also helpful to analyse the energy flows

between the building and its surroundings under different conditions. This will indicate where the major heat gains and losses are occurring. This information can be used to identify opportunities to improve performance, e.g. by increasing insulation, relocating translucent elements, etc. accordingly.


Through an interactive process involving the entire design team working with the simulation exercise it is possible to coordinate the design of the different building systems such as the envelope, lighting, mechanical systems, etc. to arrive at an integrated design that meets the specific requirements of the design brief.

11.6.2. Detailed Design At the detailed design stage, building simulation can be used to quantify the energy and indoor environment impact of design decisions in each of the areas of speciality, and in particular regarding the interactions of different building systems. At this stage it becomes necessary to provide more detailed information in preparing the model, such as the actual position and shape of windows and other translucent elements, placement of internal thermal mass, air flow and ventilation elements, lighting arrangements, HVAC systems, etc.

11.6.2.1. Envelope design Aspects of envelope design that can benefit from

simulation include the following: • Placement and capacity of thermal mass / insulating

elements and their impact on HVAC loads and / or thermal comfort.

• Interaction of daylighting strategies with artificial lighting systems.

• Geometry of shading devices at different times of day and year.

• Interaction of the mechanical systems with internal and envelope loads at different times of day and year.

11.6.2.2. Lighting design Purpose made lighting design software may be used for

detailed simulation of lighting systems. Some thermal modelling programmes are able to link to lighting software, e.g. ECOTECT and ESP-r are able to interface with the Radiance.

Particular aspects of lighting design that can benefit from

simulation include the following: • Interaction of day lighting and artificial lighting

strategies. • Checking for solar glare problems at different times of

day / year. • Ensuring that required light levels are achieved. • Determining areas that require supplemental light at

different times of day and year. • Checking on control strategies to avoid excess lighting

provision.

11.6.2.3. Mechanical systems design Building simulation programmes are a particularly

powerful tool for optimising the design of HVAC systems. They allow dynamic modelling of the interaction between climate, building fabric, occupants / equipment and the mechanical systems which cannot be achieved by static design methods. This can lead to significant savings in installed capacity. In a study of a large office building in Dublin, Beattie and Ward compared the actual installed capacity which had been designed using the CIBSE admittance method, with the design that would have been arrived at using dynamic modelling techniques. The results showed wide variations in peak cooling loads, with excess capacity of between 28% to 91% actually installed in


different zones of the building compared to the required capacity based on the dynamic modelling. (Beattie and Ward)

Particular aspects of mechanical design that can benefit

from simulation include the following: • Dynamic modelling of envelope and internal loads to

determine system capacity requirements. • Testing different system configurations to optimise the

selection of systems for heating, cooling, and ventilation.

• Optimise control systems.

11.7. Building Performance Simulation The final application of simulation to the building design process is in predicting the energy performance of the building after the design stages have been substantially completed. Simulation may be used to confirm that the building will meet the criteria set out in the Design Brief before commencing construction, and making any necessary changes. It may also be used to verify compliance with Codes and Standards, either as part of a statutory compliance procedure, or to demonstrate adherence to voluntary guidelines. Simulation may also be used to assist in lifecycle cost analysis, to predict energy costs over the life of the building. Some software packages include cost analysis

modules for this purpose. In fact LCC may in many cases be a primary optimisation parameter when choosing between options for the design.

11.7.1. Compliance with Codes and Standards. It may also be carried out as part of the procedure to verify compliance with energy standards, guidelines and regulations. Many codes for energy performance include two alternative procedures for compliance. One requires the applicant to demonstrate that each element of the building complies with the requirements of the code for that particular element, e.g. the aggregate ‘u’ value of a wall or a roof. An alternative procedure allows the applicant to demonstrate by a simulation using an approved software package that the overall performance of the building is within specified limits. An example of such a code is the ASHRAE Standard 90.1-2001 “Energy Standard for Buildings Except Low-Rise Residential Buildings”.



11.8.1. Books and papers Beattie, K.H., Ward, I.C., 1999: The Advantages of Building

Simulation for Building Design Engineers. Dublin Institute of Technology, University of Sheffield. Proceedings, IBPSA conference, Tokyo 1999. BS 1999 - cd PB-16

http://www.ibpsa.org/%5Cproceedings%5CBS1999%5CBS99_PB-16.pdf

Crawley, D. B., Hand, J.W., Kummert, M., Griffith, B.T., July 2005:

Contrasting the Capabilities of Building Energy Performance Simulation Programs. US Dept. of Energy; Energy Systems Research Unit, University of Strathclyde; Solar Energy Laboratory, University of Wisconsin-Madison; National Renewable Energy Laboratory, Golden, Colorado, USA.

(http://www.eere.energy.gov/buildings/tools_directory/pdfs/contrasting_the_capabilities_of_building_energy_performance_simulation_programs_v1.0.pdf)

Bauer, C and Groth, A. EECOB Report: Parametric simulation of

the energy performance of three generic building types in Gaborone, Botswana. Department of Energy, Government of Botswana, January 2007.

11.8.2. Codes and Standards ASHRAE Standard 90.1-2001. Energy Standard for Buildings

except Low Rise Residential Buildings.

11.8.3. Websites EDR. Energy Design Resources . http://www.energydesignresources.com/

SECTION 12 LIFE-CYCLE COST ANALYSIS ENERGY EFFICIENCY BUILDING DESIGN GUIDELINES FOR BOTSWANA Revision 1 September 2007

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Energy Efficiency Building Design Guidelines for Botswana – Section 12. Life-Cycle Cost Analysis Page 3

CONTENTS

12. LIFE-CYCLE COST ANALYSIS 4

12.1. Summary 4

12.2. Overview 4 12.2.1. Definition and description. 4 12.2.2. Opportunities 5 12.2.3. Limitations 5

12.3. Elements of Life-Cycle Cost Analysis. 7 12.3.1. Essentials. 7 12.3.2. Stages of LCC Analysis. 7 12.3.3. Stage One – Define Data. 7 12.3.4. Stage Two – Analysis. 8 12.3.5. Stage Three – Evaluation. 9

12.4. Illustrative example. 10 12.4.1. Stage One – Define Data. 10 12.4.2. Stage Two – Analysis. 11

12.5. Resource Material 12 12.5.1. Books and papers 12 12.5.2. Websites 12

Energy Efficiency Building Design Guidelines for Botswana – Section 12. Life-Cycle Cost Analysis

12. LIFE-CYCLE COST ANALYSIS

12.1. Summary This Section gives an overview of life-cycle costing (LCC)

as it is applied to building projects. The relevance of LCC to energy efficient building design in particular was discussed in Section 5, Design and Construction Process.

LCC is defined, and the opportunities and limitations of this

costing system are considered. One of a number of possible approaches to calculating LCC

is described, with references to sources for more detailed information and instructions.

An example of the application of LCC analysis is described

to illustrate how it may be used to assist in decision making at the design stage of a project.

12.2. Overview

12.2.1. Definition and description. Life-cycle Costing is defined in this context as: A method of cost analysis that estimates the total cost of a

project over a period of time that includes both the construction cost and ongoing maintenance and operating costs.

LCC is one of a number of tools that can be used to assess

the cost effectiveness of various investment options.

Others include: o Simple Payback. o Internal Rate of Return. o Net Present Value.

Simple payback is a cost analysis method whereby the annual

savings arising from an investment is estimated, and divided by the investment cost to give the number of years required to recover the cost of the investment. This may also be compared to the expected time to replacement of the system or component. For example, if a solar heater costs P12,000 and results in a saving of P1,000 per year and has an expected life to replacement of 10 years, the payback time is 12 years and it would not be financially viable to make the investment. If the annual savings is doubled (e.g. due to increase electricity cost), then the payback becomes 5 years and the investment is now viable.

Internal Rate of Return is the annualised return on

investment, based on the amount saved in relation to the amount invested. This is compared with similar indicators, such as the interest rate that could have been earned in an investment account to determine whether the investment is cost effective.

Net Present Value is a method of assessing the present value

of future costs and returns, using a ‘discount rate’ to quantify the relative value of having access to money now compared to having access to it in the future.


LCC is more complex than any one of these tools, in that it takes into consideration a greater number of relevant factors than the other methods. These include:

o Replacement cost for components or systems. o Expected time to replacement. o Maintenance costs. o Variations in projected prices for energy and other

inputs. o Variations in projected interest rates.

12.2.2. Opportunities Historically investment decisions relating to buildings have

tended to be based on estimates of the initial construction cost, with little or no consideration for costs relating to operation and maintenance throughout the life of the building.

Sharply rising energy costs have highlighted the opportunity

for overall savings in the life of a building that can be achieved by investing in more energy efficient solutions initially. Savings on other operating and maintenance costs can also be considered, e.g. using building finishes that do not need frequent re-painting.

LCC is a cost analysis tool that allows such factors to be

quantified at the design stage, so that informed decisions can be made regarding the cost effectiveness of different possible design solutions.

In some building codes it is a requirement that LCC be

applied at an early design stage to demonstrate that the

building has been designed for minimum life-cycle cost. (e.g. Iowa Code 2001).

The development of software packages that allow for

accurate simulation of the energy performance of buildings has greatly increased the effectiveness of LCC, as it is now relatively easy to predict the effect on annual energy cost of changes in the design of a building. This information is essential to allow accurate LCC analysis to be carried out.

12.2.3. Limitations As with all predictive pastimes, the output from a LCC

analysis is only as good as the input. It relies on a large number of assumptions, some of which may be quite accurate, and others that cannot be, since they are based on predictions of circumstances far into the future. With regard to energy cost, the most difficult predictions to make are those related to the future cost of energy supplies.

The decision as to how energy cost will change in the future

may have a large impact on whether a particular intervention is cost effective or not in a life-cycle analysis.

Likewise, the costs of materials, labour, finance, etc need to

be estimated for the full period under consideration, often 50 years or more, which obviously requires some very creative guesswork.

The task has been made somewhat easier in that standard sets

of assumptions for many of these variables are available, e.g. from the USA government that are required to be used for LCC analysis that relates to government codes. This means


that valid comparisons can be made between different projects. However, if the predictions are inaccurate or based on false assumptions regarding the future, then the wrong decisions may result for a large number of buildings.

Another problem lies in predicting the useful life of different

components and relating these to the time frame for the analysis. Using a longer time frame, such as the life expectancy of the building has advantages in that it allows all costs and benefits related to the project to be considered, including cost of demolition, salvage value of materials, etc. However this time frame tends to be so long that sensible predictions of costs, discount rates, rental values etc. are unrealistic.

When shorter periods are used for the analysis, care must be

taken to avoid errors arising from component replacement periods that are of a similar order to the analysis period.


12.3. Elements of Life-Cycle Cost Analysis.

12.3.1. Essentials. A life-cycle cost analysis determines the estimated cost of all

aspects of owning a building over a specified period of time. Often this is the anticipated life of the building to demolition, in which case the cost of disposing of the building may also be included. These costs are all reduced to Net Present Value (NPV), which is a measure of their value in today’s currency (i.e. 2007 Pula value).

By reducing all costs and savings to NPV, the impact of

inflation or deflation on value is removed, allowing comparisons between costs at different times in the future (or past).

The result of a LCC analysis is therefore the total cost of

owning the building over the specified period, at today’s prices. This is typically calculated for a number of alternative solutions. The results are then compared to show the relative benefits of the different alternatives. This information is then used to assist in making an informed choice between the alternative solutions.

12.3.2. Stages of LCC Analysis. Essentially LCC analysis carried out in three stages as

follows: Stage 1. Define data. Stage 2. Analysis. Stage 3. Evaluation of results.

12.3.3. Stage One – Define Data. The first stage in performing a LCC analysis is to define the

information that is needed for each option that is to be analysed.

The key data required are as follows:

o Construction cost. o Financing cost. o Recurrent operating costs.

Energy costs. Non energy costs. Maintenance costs. Cyclical maintenance. Repairs. Equipment replacement costs.

o Taxation costs and benefits. o Demolition and disposal cost. o Income generated (typically impact on productivity or

sales, sale of electricity to the grid, etc.) In each case the present value of future costs must be

estimated. This varies from current value due to two different factors.

One factor by which future costs must be adjusted is the

inflation rate, or the change in price over time. Assuming that all costs change at the same rate over time, this can be disregarded, if the analysis is carried out on the basis of constant currency, e.g. in 2007 Pula.


Generally for LCC analysis of building projects it is assumed that costs other than energy costs change at much the same rate so that variations in inflation rate can be ignored. Energy costs however tend to fluctuate independently of general inflation, so an adjustment is made for the real rate of energy cost inflation, i.e. the rate at which energy cost changes relative to general costs.

The second factor by which future costs must be adjusted is

the discount rate. This reflects the perceived difference in value of an investment made today, compared to value of the same investment being made in the future. It is generally related to the real interest rate, i.e. the rate by which interest on investments differs from the general inflation rate. Future costs are adjusted to present value by applying the discount rate over the period between the present and the time when the cost will be incurred.

Standard ‘real’ inflation rates for different forms of energy

and standard discount rates are issued by the US government for use in LCC analysis for federal buildings, to ensure a uniform approach to LCC between different jurisdictions. These are available for download at:

http://www1.eere.energy.gov/femp/pdfs/ashb06.pdf Currently the ‘real’ discount rate used for assessing

Government investment projects in Botswana is 8.0%. (pers. comm.. Dr. K. Jefferis).

No official figures for future real inflation rates for energy

sources are available in Botswana, so an informed estimate must be made.

For variables that are difficult to predict, such as future

energy price variations it is helpful to check the sensitivity of the analysis to these variables by testing a number of different values (e.g. max, min and most likely) to see the impact on the results. This gives an indication of the confidence that can be applied to the results.

12.3.4. Stage Two – Analysis. The second stage is to carry out the actual computation of

life-cycle cost for each of the alternative scenarios that are being evaluated.

The basic equation for Life-Cycle Cost is shown below (from

Fuller).

LCC = I + Repl — Res + E + W + OM&R + O Definitions:

LCC = Total LCC in present-value (PV) dollars of a given alternative

I = PV investment costs (if incurred at base date, they need not be discounted)

Repl = PV capital replacement costs Res = PV residual value (resale value, salvage

value) less disposal costs E = PV of energy costs

W = PV of water costs OM&R = PV of non-fuel operating, maintenance

and repair costs. O = PV of other costs (benefits)


A negative value for other costs (‘O’) may be included to include a value for benefits relative to a base case, for example if increased lighting levels are expected to lead to productivity gains or increased turnover.

A large number of software packages are available that can

perform the calculations of LCC, making life considerably easier for the analyst.

A very detailed book on LCC analysis is the ‘Life Cycle

Costing Manual. NIST Handbook 135’. This is available for download from the US Dept. of Energy, Energy Efficiency and Renewable Energy.

(http://www.eere.energy.gov/buildings/)

12.3.5. Stage Three – Evaluation. The final stage in a LCC analysis is to compare the results for the different cases that were analysed. LCC cost is usually only one of a number of criteria that will be considered in making a choice between different options. LCC essentially quantifies the financial costs and benefits associated with each option. Other, non-financial factors may also need to be considered, such as aesthetics, access to finance (which may be dependant on availability of collateral, or budgetary limitations), availability of equipment, skills needed for operation and maintenance, and many other considerations. For complex investment choices it is helpful to use a rational decision making tool, such as a matrix to assist in evaluating the options in accordance with all the criteria. This is done by

assigning a value for each option against each criterion, say on a score of 1-5. Each criterion is then given a weighting depending on how important it is considered to be relative to the other criteria. The outcome is then a score for each option, the highest scoring option being the most valued. Such a tool can help to guide the decision making process, but is of course always limited by the quality of the decisions that are made in applying it.


12.4. Illustrative example. A simple example of LCC analysis is provided to illustrate

how the process works. This example was calculated using Energy eVALUator, a

simplified tool for life-cycle cost analysis from Energy Design Resources.

The example uses a typical classroom building for which an

energy performance simulation has previously been carried out using DesignBuilder and Energy Plus software. LCC analysis is used to evaluate the cost implication of providing 100mm of ceiling insulation, or using white roof sheets to reduce energy cost.

12.4.1. Stage One – Define Data. Item Baseline Insulated

CeilingWhite roof

sheets Building floor area [m2] 160 160 160 General inflation [%] 0 0 0 Electricity inflation [%] 5 5 5 Analysis period [yrs] 15 15 15 Project cost [P] 400,000 404,800 402,400 Discount rate [%] 8 8 8 Initial Energy expenses [P/yr]

4,330 3,505 3,440

Other operational expenses [P/yr]

1,792 1,792 1,792

Table 12.1 Input data for LCC. The input data was determined as shown in Table 12.1

It was assumed that the construction cost was paid for without loan. A discount rate of 8% was used, which is the recommended for government investment appraisals (see above). The analysis was performed at current Pula prices to remove the effect of inflation from the comparison. A differential inflation rate of 5% for energy costs was included to allow for energy costs to escalate at 5% more than other costs. A 15 year period was selected for the analysis.

Energy eVALUator is a simple-to-use Windows-based program for calculating the life cycle benefits of investments in improved building design. Energy eVALUator is designed to analyze improvements that reduce energy cost, improve employee productivity, and enhance tenant satisfaction. The tool is designed to help building owners, developers, tenants, architects, engineers, and facility managers by providing the financial information necessary for making decisions based on the economic merits of improved building design.


12.4.2. Stage Two – Analysis. This data was input into a project in the eVALUator software package which performed the necessary calculations. Output reports were generated that compare the LCC for both the alternatives with the baseline case and also provide the simple payback periods. The results were as follows:

Item Baseline Insulated Ceiling

White roof sheets

Analysis period [yrs] 15 15 15Project cost [P] 400,000 404,800 402,400Energy expenses [P] 52,229 42266 41,494Non energy expenses [P] 15,339 15,339 15,339Total life cycle costs [P] 467,568 462,405 459,233Simple payback [yrs] - 5.8 2.7

Table 12.2 Results of LCC. Cash Flow reports were also produced and used to provide a

graph showing the incremental savings achieved by both interventions. These illustrate the simple payback, which occurs were the incremental savings become zero as shown in Fig. 12.1

Fig. 12.1 Incremental savings.

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12.4.1. Stage Three – Evaluation. The results indicate that both ceiling insulation and using

white roof sheets are cost effective strategies for reducing energy cost.

Using white coloured roof sheets is the preferred alternative,

since it gives a shorter simple payback time, as well as a lower total life-cyle cost.

A further analysis could be carried out to determine the

impact of combining both strategies, using white coloured roof sheets and providing insulation over the ceiling. This would first require a further energy simulation to determine the effect on energy consumption, before the LCC analysis can be carried out.

The strength of LCC analysis is that it allows a rational

choice to be made, that would otherwise be based on hunches and guesswork. The weakness is the time and effort that it costs to carry out the analysis. This is greatly reduced by the availability of simple software tools that do most of the work.


12.5.1. Books and papers Fuller, Sieglinde. Life-Cycle Cost Analysis (LCCA).

National Institute of Standards and Technology (NIST) (http://www.wbdg.org/design/lcca.php) Fuller, Sieglinde and Petersen, Steven. Life Cycle Costing Manual

for the Federal Energy Management Program. NIST Handbook 135. 1995 edition. US Dept. of Energy.

Rushing, Amy S. and Fuller, Sieglinde K. Energy Price Indices and

Discount Factors for Life-Cycle Cost Analysis - April 2006 Annual Supplement to NIST Handbook 135 and NBS Special Publication 709

12.5.2. Websites EDR. Energy Design Resources . http://www.energydesignresources.com/ US Dept. of Energy, Energy Efficiency and Renewable Energy. http://www.eere.energy.gov/buildings/ WBDG Whole Building Design Group http://www.wbdg.org

SECTION 13 APPENDICES


Energy Efficiency Building Design Guidelines for Botswana – 13.APPENDICES Page 3

CONTENTS

1. PROPERTIES OF BUILDING MATERIALS 4

2. PROPERTIES OF BUILDING ELEMENTS - ROOF 5

PROPERTIES OF BUILDING ELEMENTS - WALLS 5

PROPERTIES OF BUILDING ELEMENTS - FLOOR 6

3. PROPERTIES OF GLASS 9

4. ASHRAE STANDARD 90.1 2001 (extract). 10

Energy Efficiency Building Design Guidelines for Botswana – Section 13. APPENDICES

1. PROPERTIES OF BUILDING MATERIALS

Density Specific heat Conductivity Source

kg/m3 J/kg.K W/m.K

Insulating materialsPolystyrene 15 1.4 0.037 aGlasswool 12 0.042 ePVC 1390 900 0.17 bPVC floor covering 0.4 aWoodwood cement 908 0.282 e

Concrete, brick and plasterPlasterboard 0.159 aConcrete medium density 1800 1000 1.35 bCast concrete 2000 1000 1.13 bPlaster (dense) 1300 1000 0.5 bVermiculite plaster (light) 480 880 0.144 aVermiculite plaster (dense) 960 880 0.303 aBrick (average) 1.21 a

Energy Efficiency Building Design Guidelines for Botswana – Section 13. APPENDICES Page 5

Density Specific heat Conductivity Source

kg/m3 J/kg.K W/m.K

Aggregate, rock and clayGranite 2.92 aSandstone 1.295 aBuilding sand 1500 840 0.3 aSlate 2500 750 1.4 aSoil 1500 850 1.5 aClay tiles 1922 920 0.84 a

TimberPine timber 500 2800 0.15 dHardwood (American Beech) 560 - 865 390 0.173 c

MetalsLead 11340 1900 34 a,cCast iron 7200 520 50 dSteel 7870 4860 51.9 cAluminium 2698 900 210 cCopper 8960 385 385 cSilver 10491 234 419 c

OtherAir 1.3 1 0.032 dWater 998 4182 0.609 cConcrete 2250 1000 2 dGlass 2500 700 1 d


2. PROPERTIES OF BUILDING ELEMENTS Construction thickness R value U value C CR Source

layers mm m2.K/W W/m2.K kJ/m2.K sec

ROOFGalvanised roof 0.190 5.263 22.949 4.360 a

Galvanised sheet 0.6 22.949

Galvanised roof with ceiling 0.530 1.887 27.449 14.548 aGalvanised roof 0.6 22.949Ceiling 10 4.500

Galvanised roof with 50mm insulated ceiling 2.030 0.493 27.450 55.724 aGalvanised roof 0.6 22.949Fibre glass insulation 50 0.001Ceiling 10 4.500

Galvanised roof with 100mm insulated ceiling 3.420 0.292 27.451 93.883 aGalvanised roof 0.6 22.949 a100mm fibre glass insulation 100 0.002Ceiling 10 4.500

Thatch 4.500 0.222 aThatch 250

Concrete tiles with underlay 0.345 2.897 56.250 19.406 bConcrete tiles 25 56.250Air gap 25 0.000Polythene 0.1 0.000


Construction thickness R value U value C CR Sourcelayers mm m2.K/W W/m2.K kJ/m2.K sec

WALLS

Solid half brick wall plastered 0.311 3.215 228.000 70.908 bPlaster 15 19.500Cement brick 105 189.000Plaster 15 19.500

Hollow block wall plastered 150mm 0.410 2.439 201.000 82.410 aPlaster 15 19.500Hollow cement block 150 162.000Plaster 15 19.500

Hollow block wall plastered 230mm 0.510 1.961 287.400 146.574 aPlaster 15 19.500Hollow cement block 230 248.400Plaster 15 19.500

Solid one brick wall plastered 0.394 2.538 435.000 171.390 bPlaster 15 19.500Cement brick 220 396.000Plaster 15 19.500

Cavity wall plastered 0.567 1.764 417.000 236.439 bPlaster 15 19.500Cement brick 105 189.000Air gap 50 0.000Cement brick 105 189.000Plaster 15 19.500

Cavity wall plastered with insulation 1.955 0.512 417.001 815.237 bPlaster 15 19.500Cement brick 105 189.000Air gap 50 0.000Glass wool 50 0.001Cement brick 105 189.000Plaster 15 19.500


Construction thickness R value U value C CR Source

layers mm m2.K/W W/m2.K kJ/m2.K sec

FLOORS

Concrete on DPC 0.231 4.329 200.626 46.344 bCast concrete 100 200.000PVC 0.5 0.626

Sources: a. Hamilton, L.B., et. al. 1984. Passive Solar Design Workbook. BRET. Botswana. b. EECOB Report: ‘Parametric simulation of the energy performance of three generic building types in Gaborone, Botswana’. Department

of Energy, Government of Botswana, January 2007. c. Matweb Material Property Data. http://www.matweb.com d. University of Warwick. Department of Engineering. Data Book 1977 e. National Institute of Standards and Technology, USA. Standard Reference Database 81. http://srdata.nist.gov/insulation/


3. PROPERTIES OF GLASS

Description Visible lightTransmission

[%]

Solar energy Transmission

[%]

Visible/Solar Transmission

[ratio]

Shading coefficient

[ratio]

U value [W/m2°C]

Clear float glass 1.00 SolarVue Blue – High Light 38 47 0.81 0.54 5.8 SolarVue Blue – Extra High Light 46 53 0.87 0.61 5.8 SolarShield Blue – S10 9 25 0.36 0.28 5.8 SolarShield Blue – S20 20 33 0.61 0.38 5.8 SolarShield Blue – S30 30 41 0.73 0.47 5.8 CoolVue Clear 72 47 1.53 0.54 5.8 InsulVue Coolblue (ColourVue +12mm air gap + ClearVue)

65 61 1.07 0.71 3.2

InsulVue Blue (SolarShield +12mm air gap + ClearVue) – S10

8 16 0.50 0.19 3.2


18 24 0.75 0.27 3.2


26 31 0.84 0.35 3.2

Table 3.1. Properties of Glass (from Smart Glass Catalogue, PFG Building Glass) Notes: The “Shading Coefficient” is the ratio of Total Solar Energy Transmission of a glass compared to the Total Solar Energy Transmission

for ordinary 3mm glass. The ratio of Total Visible Light Transmission compared to Total Solar Energy Transmission has been included to give a comparison of

which glass is most effective at transmitting maximum light with minimum energy. The higher the 'Visible Light Transmission', the clearer the glass will appear. The higher the 'Solar energy transmission', the more heat the glass is allowing into the building. Thus the ideal glass would have high Visible Light Transmission and low Solar energy transmission.


4. ASHRAE STANDARD 90.1 2001 (extract). Extract from : ASHRAE Standard 90.1 2001 Energy Standard for Buildings except Low Rise Residential Buildings Climate data for Pretoria are given in Table 4.1. and the corresponding values for envelope requirements are given in Tables 4.2. and 4.3. Climate parameter ValueLatitude 25.73SLongitude 28.28EElevation 1,330Heating Degree Days base 18°C 639Cooling Degree Days base 10°C 3,238Heating design Temp. 99.6% 4Cooling Design Temp DB 1.0% 31Cooling Design Temp WB 1.0% 17

Table 4.1. Climate data for Pretoria (source: ASHRAE Standard 90.1-2001 Table D3)


Wall, mass: a wall with a heat capacity exceeding (1) 143 kJ/m2K or (2) 102 kJ/m2K provided that the wall has a material unit weight not greater

than 1920 kg/m3 Wall, metal building: a wall whose structure consists of metal spanning members supported by steel structural members (i.e., does not include spandrel glass

or metal panels in curtain wall systems). Wall, steel framed: a wall with a cavity (insulated or otherwise) whose exterior surfaces are separated by typical steel stud walls systems). Wall, wood framed and other: all other wall types, including wood stud walls. Floors, mass: a floor with a heat capacity exceeding (1) 143 kJ/m2K or (2) 102 kJ/m2K provided that the wall has a material unit weight not greater

than 1920 kg/m3 Assembly max SHGC: solar heat gain coefficient (SHGC): the ratio of the solar heat gain entering the space through the fenestration area to the incident

solar radiation. Solar heat gain includes directly transmitted solar heat and absorbed solar radiation, which is then reradiated, conducted, or convected into the space.

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