INTEGRATING COST & ENGINEERING CONSIDERATIONS 

IN

DESIGNSJAYGOPAL KOTTILIL

Senior Manager (MEP Engineering)Doha14th May 2014

What & Why HVAC ???

Heating, Ventilating, Air‐Conditioning

Traditional Zero‐Energy Air‐Conditioning

Modern Day Air‐Conditioning

Temperature

Relative Humidity

Noise Level

Indoor Air Quality

Life Safety

HVAC in Real Estate Developments

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Reliable

Robust

Safe

Economical

Sustainable

Real Estate Developments ‐ Financials

Expenditure• Capital / First Cost• Operating Cost

Revenue

Return on Investment

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Real Estate Developments ‐ Capital Expenditure

Land

Infrastructure

Building

Professional fees

Financing & Insurance

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Real Estate Developments ‐ Operating Expenditure

Utility (Electricity, Water, District Cooling, LP Gas, Telecom etc.)

Facility Management (Maintenance, Replacements, etc.)

Marketing

Finance & Insurance

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Real Estate Developments ‐ Revenues

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Real Estate Developments ‐ Return on Investment

Capital cost recovery per year spread over ‘n’ years Operating cost recovery annually

A. Total expenditure recovery per annumB. Total revenue per annum

Minimize expenditure!             Maximize revenue!

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Infrastructure Capital Cost

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25%

5%

15%

20%

25%

10%

Electricity

Street lighting

Potable water

Drainage (Sewer and Stormwater)

District cooling

Telecommunication

Building Capital Cost

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27%

19%

22%

15%

17%

Structure

Envelope

Mechanical

Electrical

Interior finsihes

M+E Capital Cost

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28%

5%

4%

27%

8%

6%

7%

15%HVAC

Plumbing

Drainage

Electrical power

Voice and Data

ELV

Fire detection & protection

Sanitary appliances

Sustainable Developments Qatar National Vision 2030

• Economic Growth, Social Development and Environmental Management• Economic development and protection of the environment ‐ neither of which 

should be sacrificed for the sake of the other

Sustainable Developments• Urban Connectivity • Site

• Materials

• Outdoor Environment• Cultural & Economic Values

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Electricity Usage in Qatar

0% 5% 10% 15% 20% 25% 30%

Residential buildings

Commercial buildings

Industrial use

Others

Plant use

Losses

HVAC Component

Residential buildings: 60%

Commercial buildings: 50%

Engineering Objectives

Optimize First Cost              Reduce Energy                  Conserve Water

Sustainable design Be compassionate to the end‐user

Engineering Objectives

always, always,

Always Remember …

HVAC Engineering Design Considerations

MAXIMIZE design accuracy & efficiency

RESIST over‐designing

PREVENT over‐engineering

Engineering DesignDesign is an iterative process …… progresses through different stages

ARCHITECT

STRUCTURAL ENGINEER

HVAC ENGINEER

PLUMBING ENGINEER

ELECTRICAL ENGINEER

LIGHTING DESIGNER

ELV ENGINEER

FIRE PROTECTION ENGINEER

DESIGN/PROJECT MANAGER

COST MANGER

Design Accuracy

* According to BSRIA BG/6 A Design Framework for Building Services 2nd edition

Conventional RIBA Definition Design Accuracy *

Concept Concept Stage C ± 25%

Scheme Design Development Stage D ± 20%

Detailed Technical Design Stage E ± 15%

Tender Documents Production Information Stage F ± 5%

Over‐designHow? Application of incorrect design criteria (internal/ external criteria) Use of static design techniques Over‐use of design margins in rudimentary calculations Safety margins applied to plant & equipmentConsequences of over‐designed systems Occupies additional space and volume Loss of leasable/saleable area Increased capital cost Increased operating cost due to inefficient operation Increased utility charges (particularly for district cooling applications)

Over‐engineering

Over‐engineering is not Over‐design.

Over‐engineering results from over specifying materials, equipment and installation details.

Over‐engineering is normally addressed through value engineering exercise.

Initial Cooling Load Estimate Initial concept appraisals will be based upon W/m2 unit area. Rule of thumb values typically are,

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Design Temperature Criteria

External: 46OC & 33% RH (30OC wet bulb T) Indoor comfort: 24OC & 50% RH

Static Building Heat Gains

Solar Radiation Convention

Transmission Conduction

Infiltration Internal Lights Occupants Equipment

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Cooling Load Components

External loads Solar heat gain through fenestrations (windows) Conductive heat gain through fenestrations Conductive heat gain through exterior walls and roofs Conductive Heat gain through partitions & interior doors Heat gain from outdoor air infiltration

Internal loads People Electric lights Equipment

Ventilation load (Outdoor air tempering)27

Heat Gains through Fenestration

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Fenestration types

(Source: GUARDIAN Glass)

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Heat Transfer ‐ FenestrationSolar Heat Gain Coefficient (SHGC)• Percentage of solar energy incident on the glass that is 

transferred indoors (directly and indirectly)• Direct heat gain – Solar energy transmitted• Indirect heat gain – Solar energy absorbed and 

reradiated/convected

Shading Coefficient (SC)• Considers shading and tinting of glass

• SC = SHGC ÷ 0.87 approximatelyFor monolithic clear 3mm glass, SC=1.00 and SHGC=0.87

Thermal Conductance Value (U) expressed in W/m2.OK• Heat gained/lost due to the difference between indoor and 

outdoor air temperatures

Fenestration comparison

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(Credit: GUARDIAN Glass)

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Typical case

• Burj Khalifa features more than 174,000 m2 of fenestration

• High thermal performance glazing

• SHGC ˂ 0.25 (SC ˂ 0.29)

• U‐Value ˂ 2.00 W/m2.OK

(Source: GUARDIAN Glass)

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External walls exposed  to sun

Walls

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Heat Gains Conversion into Cooling Load 

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Infiltration – Common Air Leakage Paths

Driving Mechanisms for Infiltration

Stack effect ‐ Air density differences due to indoor and outdoor air temperatures

Wind pressure

Building cracks and openings

Realistic Infiltration Estimate Method

Actually occurs at the perimeter façade

Practical calculation ‐ based on façade area & expected air‐tightness (Typical facade air‐tightness values 0.6 – 1.4 L/s.m² facade area at 50 Pa)

In reality, occurs at all times and can be positive or negative depending on wind conditions; generally an average value is used

Can be suppressed to some extent by pressurization of the building

Estimating Infiltration

Maximum Average Air Infiltration rates in Air Changes per hour (AC/h)CIBSE Guide A –

Table ref. Building ‘Leaky’ building Moderately ‘tight’ building

Table 4.15 Office : Air conditioned, 2000–8000m2 0.60 0.20

Table 4.16 Office : Air conditioned HQ‐type building, 4000–20000 m2 0.65 0.25

Table 4.17 Factories, Warehouses, Halls 0.65 0.25

Table 4.18 Schools 0.70 0.25

Table 4.19 Hospitals and Health Care buildings 0.60 0.25

Table 4.20 Hotels 0.85 0.30

Table 4.21

Dwellings – 1 floor 1.15 0.40

Dwellings – 2 floors 1.00 0.35

Apartments – 1 to 5 floors 1.00 0.50

Apartments – 6 to 10 floors 1.60 0.55

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Internal Heat Gains

Electric lights

People

Equipment and appliances

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Internal Heat Gain ‐ Lights

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Internal Heat Gain ‐ Lights

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Internal Heat Gain ‐ Lights

Heat from ceiling‐recessed luminaires has two (2) components

Heat to conditioned space Heat to ceiling plenum

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Internal Heat Gain ‐ Occupants

Anticipated simultaneous occupancy – Furniture scheme OR ASHRAE 62.1 Degree of activity

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Internal Heat Gain ‐ Equipment Estimate heat gains from equipment for anticipated simultaneous 

operation. ASHRAE Handbook of Fundamentals provides guidance.

35 W/m2

8 W/m2

17 W/m2

Final (Dynamic) Cooling Load

Represent orientation of the  building and the way in which the owner will operate the building. 

Use dynamic energy/ thermal simulation of a 3D model of the building using proprietary simulation software.

Undertake modeling as soon as the architectural form has been substantially  developed so that utility loads can be assessed as early as possible.

From experience the results of dynamic simulation have reduced the rule of thumb cooling loads by 30 – 40% and 20 – 25% lower than a static model.

The reductions are assisted by incorporating the demand controlled fresh air and energy recovery features into the simulation. 

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Dynamic Thermal Model

Un‐rendered 3‐D building models can be imported into simulation software 

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Dynamic Thermal Model

o Thermal templates are created and assigned to the room spaces and zones.o Incorporate internal heat gain data specific to the space.

Schedules are created according to room type for all internal gains (occupancy, lighting, etc.).

Dynamic Thermal Model

Dynamic Thermal Model

Dynamic thermal model utilizes profiles for internal gains Peak loads of different zones do not occur at corresponding times When considering peak coincidental load, many of the variable peaks do 

not occur at corresponding times In static load calculations, these variable peaks are summated

0

500

1,000

1,500

2,000

2,500

3,000

Internal gain(kW)

Solar gain (kW) Externalconduction gain

(kW)

Infiltration gain(kW)

Sensible CoolingLoad (kW)

Total  CoolingLoad (kW)

1,723

280 371 259

2,213

2,633

1,253

245 346 244

1,8682,025

100% Static Model

Profiled Dynamic Model

Fresh (Outdoor) Air Management

Fresh air treatment (tempering) can constitute 30 ‐ 40% of the total cooling load

1.0 m³/sec of fresh air = 40 kW / 11.5 TR cooling energy with energy recovery devices

1.0 m³/sec of fresh air = 72 kW / 20.5 TR cooling energy without energy recovery devices

Fresh air distribution sizing will be based upon 100% zonal requirements but they will not necessarily occur simultaneously

To minimize impact on plant capacity & operating cost:

Use energy recovery devices (Heat wheel, Run‐around‐coil, Heat pipe, etc.) Variable volume fresh air distribution system (VFD fans) Demand controlled fresh air (Use of CO2 sensors) Occupancy profiles for the respective spaces (Timed operation)

Design Margins

Cooling loads ‐ 10% on sensible load; 5% on latent load

Flows ‐ 5% on calculated value

Pressure ‐ 10% on calculated value

Terminal equipment ‐ 5 to 10% over zone cooling load

On site cooling plant ‐ 10% over coincidental cooling load

District cooling service ‐ 0% on coincidental cooling load (even slightly under‐subscribing DC service is in order)

0.90 1.10 1.60 1.40 1.80

District coolingsystem

Water cooledchiller system

Air cooled chillersystem

Air cooled VRFsystem

Split AC system

kW/TR

Costs ‐ Cooling Systems

 ‐

 2,000

 4,000

 6,000

 8,000

 10,000

 12,000

 14,000

 16,000

District coolingsystem

Water cooled chillersystem

Air cooled chillersystem

Air cooled VRFsystem

Split AC system

QAR/TR

District cooling system

Water cooled chiller system

Air cooled chiller system

Air cooled VRF system

Split AC system

30‐Year Capital Expenditure

30‐Year Maintenance Expenditure

30‐Year Utility Expenditure

30‐Year Life Cycle Expenditure

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Design Principles ‐ Recap

o Use correct external and internal design temperatures

o Select right fenestration materials

o Design heat resistant external walls and roof

o Select energy efficient lighting luminaires

o Adopt correct dynamic occupancy  & activity levels

o Use established equipment heat gains

o Allow infiltration based on façade area & expected air‐tightness 

o Undertake dynamic thermal modeling

HVAC Road Map

Set up statutory regulatory body for design verification

Integrate and regulate design criteria for all building types

Establish and benchmark design efficiency and energy use

Audit designs prior to issuance of building permit

Development Processes

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