lisa iszatt - thesis - material configuration: the relationship between thermal capacitance and...

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Lisa Iszatt July 2007 Material Configuration ii

Material Configuration: The Relationship Between Thermal Capacitance and Resistance in an

Extruded Clay Block

Lisa Iszatt

A thesis submitted to the School of Computing and Technology, University of East London, as a requirement for a degree of MSc

Architecture: Advanced Environmental and Energy Studies

July 2007

Lisa Iszatt July 2007 Material Configuration i

Preface This thesis investigates the use of less environmentally harmful materials to give the equivalent thermal comfort benefits of concrete block wall systems, through the addition of a thermally heavy material. Thermal mass is increasingly identified within the building industry as a major tool in reducing over heating. In the UK climate this has traditionally been limited to high occupancy buildings, but with the UKCIP021 scenarios predicting extreme temperature rises over the next century the need to design housing for future climates has arisen. The problem with using concrete blocks to provide thermal mass is that large amounts of energy are used in production of both the blocks themselves, and of the cement mortar and rigid insulation that the wall system requires. It is widely believed that the embodied energy is justifiable as it is dwarfed by the energy use over the lifetime of a building2. However, as more efficient buildings are produced, this proportion becomes more significant. There are a number of other environmental issues on which heavy weight concrete block wall systems also score badly. Of surprising enormity are water extraction (approximately 625 litres per square metre of wall system), and ecotoxicity pollution to water (approximately 260 m3tox per square metre of wall system) 3. Extruded clay blocks (ECBs), although not completely benign are less environmentally harmful in material use and production. They also have the benefit of efficiency over non-module or completely unfired clay products, making them more commercially viable. ECBs are continually modified to improve thermal resistance. This has been explored for decades by a range of manufacturers and has resulted in different configurations of block, using various sizes and shapes of air void as insulation. This thesis explores the possibility of using the configuration of the ECB to enhance thermal performance; adding thermal mass to the inside face of the block, by varying the density. Experiments are conducted using a physical test cell and two types of computer based modelling to test various configurations of block against concrete blocks. Clay powder is used to fill the gaps of an existing ECB and the reactions to dynamic heat flow are tested. Temperatures both sides and throughout the blocks are analysed.

The following conclusions are drawn regarding environmental savings:

- ECBs with 4 to 6 rows filled with clay create similar thermal environments to medium weight concrete blocks, in UK high-density office scenarios.

Assessment was made of consequent environmental savings, which indicated: - 30.6% and 25.4% reductions in CO2 emissions respectively, - Between 62.1% and 99.6% savings for other environmental indicators including pollution

to air and water, water extraction, waste disposal and transport pollution and congestion4

The following conclusions are drawn regarding thermal mass location within walls:

- The current orthodoxy of locating thermal mass close to the inside face of a wall for maximum thermal benefit is verified.

1 UKCIP (2002) - Predicts future UK temperatures based on various scenarios of greenhouse gas emissions 2 For example Webb (2007) 3 Derived from BRE (2002-a,b,c,d & 2006). See chapter 11. 4 For units and more detail, refer to chapter 12: Tables 12.1 a & b.

Lisa Iszatt July 2007 Material Configuration ii

- Fixed volumes of mass at varying distances from the material edge give greater results than increased volumes of mass at a fixed distance.

Recommendations for future research to address identified limitations of ECBs include:

- Investigations into the extrusion process to create more extreme configurations.

The intention would be to vary the structural line and therefore void sizes, to allow distinction between thermal mass and protected insulation. This could potentially reduce block widths and the need for sacrificial polystyrene in the firing process. Larger physical testing, and development of HFS models is also recommended, to verify the results of this thesis and to test the thermal behaviour of more extensive configurations of block.

Acknowledgements

This thesis was made possible by information, advice and support from various sources. Grateful thanks are given to the following:

Mike Thompson and all of the MSc: AEES staff, for conceiving and developing such an

inspiring course; Melissa Taylor, my thesis supervisor, for advice on developing the scope of investigation,

and for enthusiasm and encouragement; Bobby Gilbert, for originally developing the Heat Flow Spreadsheet, for on-going advice

on its use and for his clarity in explaining complicated issues. Also for developing a U-Value Calculator Spreadsheet which helped to inform the process of test cell results analysis, and for guidance in using IES;

Lawrence Brown for his helpful guidance on building and developing the test cell and analysing results. Also for the lending of the data logging kit;

Simon Earland, of Earland Engineering and the Heat Transfer Society, for checking, verifying and correcting aspects of the explanation of heat transfer through voids. This section was developed from methods explained in JP Holman’s Heat Transfer, as recommended by Bobby Gilbert.

Simon Tucker, for the thorough explanations of thermal mass given in course lectures and his paper Simplified Thermal Assessment in the A6 Unit Book, from which research leads for chapter 3 were drawn. Also for guidance in IES.

My colleagues at Architype ltd, for creating a stimulating and supportive environment, particularly Peter Griffiths and Ben Humphries for proof reading;

Werner Holfeld of Ziegel in Germany, and Richard Cook of Natural Building Technologies for material data;

Francis Iszatt and Geoff Williams for research input; Kristin Trommler for interviewing Albert Sommer of Ziegel on my behalf; Jana Iszatt, Toby and Claudia Stuable, for translating German texts; Daniel Grint, for general sustenance and support.

Lisa Iszatt July 2007 Material Configuration iii

Contents Chapter 1 Introduction .…………………………………………………………………………01 1.1 Background ……………….…………………………………………………………01 1.2 Overview ......……………….………………………………………………….…02 Chapter 2 Extruded Clay Blocks (ECBs) ………...…..………...……………….………03 2.1 Introduction .…………………………………………………………………………03 2.2 Materials and Production Process …….…………………………………………03 2.3 Use in construction ………………..…….…………………………………………04 2.4 Use in the UK ………………………...…….…………………………………………04 2.5 Configurations ………………..…….…………………………………………05 2.6 ECB Physical Dimensions & Properties ………………………………………05 2.7 Adjustments to ECBs …………………..….…………………………………………06 Chapter 3 Thermal Mass …………………..……...…..…………………..…………….07 3.1 Thermal Capacitance and Thermal Resistance …………………...…………07 3.2 Current Standards ………………..…….…………………………………………07 3.3 Benefits and Drawbacks of Thermal Mass ………………………………………08 3.4 Factors Affecting Thermal Mass …….…………………………………………08 3.5 Summary ……….………………..…….…………………………………………10 Chapter 4 Methodology …………………..……...…..……………………………..……..……11 4.1 Introduction …………………………………………….………………...…………11 4.2 Physical Test Cells ………………..…….…………………………………………12 4.3 Computer Simulation: IES ………………………..………………………………12 4.4 Heat Flow Spreadsheet ……….…….…………………………………………13 4.5 Summary ………………..……….…….…………………………………………13 Chapter 5 Process: Material Properties Analysis ...……………………….……………14 5.1 Introduction …………………………………………….………………...…………14 5.2 Thermal Transfer Through Voids ……….………………………………………14 5.3 Derivation of ECB Solid Element Properties .....…..………………………………17 5.4 Derivation of Layer Properties For IES and HFS Models …..…………………18 5.5 Summary ………………..……….…….…………………………………………19 Chapter 6 Process: Physical Test Cell ………....……………………….……………21 6.1 Introduction …………………………………………….………………...…………21 6.2 Set Up ……….………………..…….…………………………………………21 6.3 Equipment …………………..……………………..………………………………23 6.4 Method ………………..……….…….…………………………………………25 6.5 Calculations …………………………………………….………………...…………25 6.6 Assumptions & Inaccuracies ……………..…………………………………………28 6.7 Summary …………………..……………………..………………………………30 Chapter 7 Process: Computer Simulation: IES ……………………...………….……31 7.1 Introduction …………………………………………….………………...…………31 7.2 Test Cell Calibration Set Up ………….….…………………………………………31 7.3 Buffered T14 Office ……….....……………………..………………………………32 7.4 Semi Buffered T11 Office ……….…….…………………………………………32 7.5 Stand-Alone T11 Office ………..………………….………………...…………32 7.6 Limitations of the IES Models ……………..…………………………………………32 Chapter 8 Process: Heat Flow Spreadsheet ……….……………...………….……………34 8.1 Introduction …………………………………………….………………...…………34 8.2 Mathematical Background of Existing HFS ………………………………………34 8.3 Method and Adaptations ....……………………..………………………………36 8.4 Limitations of the IES Models ……………..…………………………………………38 Chapter 9 Results: Steady State Analysis ……….……………...………….……………39 9.1 Test Cell Results .…………..……………………….………………...…………39 9.2 IES Results …….……………………………………………………………………41

Lisa Iszatt July 2007 Material Configuration iv

Chapter 10 Results: Dynamic Analysis ……….……………...………….……………43 10.1 Test Cell Results .…………..……………………….………………...…………43 10.2 IES Results …….……………………………………………………………………44 10.3 HFS Results …….……………………………………………………………………47 Chapter 11 Results: Scaling Up …………………..…….……………...………….……………50 11.1 Introduction ...…..…...……..……………………….…………….……...…………50 11.2 Office 1: 16Sqm / T14 configurations ..……………...………………………………50 11.3 Office 2: 16Sqm / T11 configurations & Concrete blocks ……...……….…..…51 11.4 Office 3: 240Sqm / T11 configurations & Concrete blocks …...………….……..57 Chapter 12 Implications and Recommendations For Further Research ..…………..60 12.1 Introduction ...…..………….……………………….…………….……...…………60 12.2 Environmental Savings ………...……………..……………………………….60 12.3 Production ...…..…………..………………..…….…………….……...……….…61 12.4 Buildability ...…..…………..………..…………….…………….……...……….…62 12.5 Cost ………....…..…………..………..…………….…………….……...……….…62 12.6 Summary ...…..…………..….…….…………….…………….……...……….…63 Chapter 13 Conclusions ………...………….………..…….…………...………….……………64 13.1 ECB Comparisons to Concrete Blocks ....…..….…………….……...………64 13.2 ECB Limitations ………...………….…………...………………………………65 13.3 Location of Thermal Mass ……….………………....………….……...………….66 13.4 Scope and Limitations of the Thesis ….……………...…………….…..............…66 Appendices ………...………….………..…………………..….…………...………….……………67 References ………...………….……….………….……..…….…………...………….……………69 Bibliography ………...………….……….………….……..…….…………...………….……………70

List of Figures

2.1 ECBs on site: Thin bed mortar being applied between courses ……........................04 2.2 ECB Various Configuration Types for ECBs ……...…....................................................05 2.3 ECB Physical Dimensions of T14 365 ..................................................................05 2.4 Specific and Volumetric Heat Capacities for Various Materials ...............................06 2.5 Clay Added to ECB .…..…..............………….…...…....................................................06 2.6 Heat Transfer Mechanisms Through ECB ..................................................................06 3.1 Diurnal capacities of different materials ……….......................................................09 3.2 Proportional Areas Needed of Exposure to Types of Gain for Comparative Thermal Mass Benefits ………............................................10 5.1 Properties of Air at Atmospheric Pressure ..................................................................16 5.2 Derivation of Thermal Conductivity for ECB Solid Elements ...........................................18 5.3 Assumed Extent of 1D Heat Flow Through Single ECB ...........................................19 5.3 Assumed Extent of 1D Heat Flow Through ECB in Series ...........................................19 6.1 Exploded View of Test Cell Set Up ..............................................................................21 6.2 Plan View of Test Cell Set Up ..............................................................................22 6.3 Section Through Test Cell Set Up ..............................................................................22 6.4 Photos of Equipment .....................................................................................................24 6.5 ECB & Clay Powder .....................................................................................................25 6.6 Thermocouple Positions Through ECB ..................................................................25 6.7 Hot Box Construction .....................................................................................................28 6.8 Heat Transfer Mechanisms Through Hot Chamber .....................................................29 6.9 Heat Transfer and Infiltration Through Test Cell ..........................................................29 7.1 IES: Test Cell Calibration Set Up…...….........................................................................31 7.2 IES: Multiple Test Cell View…...…..................................................................................31 7.3 IES: Semi Buffered Office Diagram …............................................................................32 8.1 HFS: Position of Nodes Through ECB ..................................................................34 8.2 HFS: Spreadsheet Set Up in Excel ..............…............................................................35

Lisa Iszatt July 2007 Material Configuration v

8.3 HFS: Spreadsheet Set Up – Caclculation Precedents ...........................................36 8.4 HFS: Spreadsheet Set Up– The Effect of Introducing Heat Gains.................................37 9.1 TC:Hot Chamber and ECB middle air temperature above CC temperature....................39 9.2 TC: Temperature differences through ECB for configuration OC .................................40 9.3 TC: Temperature differences through ECB for configuration 9C.................................41 9.4 IES: Steady State Profiles for 2 Layered and 10 Layered Models……………................41 9.5 IES: Temperature Differences at Power Off…………………….……………................42 10.1 TC: Dynamic Temperature Profiles of Configurations 0C to 9C………………..............43 10.2 TC: Dynamic Temperature Profiles at Peak Temperatures…..………………..............44 10.3 IES: Dynamic Temperature Profiles for 2 Layered and 10 Layered Models…..............45 10.4 IES: Dynamic Temperature Profiles at Peak Temperatures……………….…..............45 10.5 IES: Anomalies in Temperature Around Peak……………….…...................................46 10.6 HFS: Dynamic Temperature Profiles in a 1m3 Test Cell……….….............................47 10.7 HFS: Dynamic Temperature Profiles: Increasing Void Before Fixed Volume of Mass………….….........................................48 10.8 HFS: Dynamic Temperature Profiles: Configurations 0C to 5C………….…...............48 10.9 HFS: Dynamic Temperature Profiles: Increasing Mass After Fixed Void……………..………….….........................................49 11.1 IES Office 1 – Temperature Profiles Over 3 Days…………..…...................................51 11.2 IES Office 2 – T11 Temperature Profiles Over 1 Week…………..............................52 11.3 IES Office 2 – T11 - Tuesday and Wednesday……………......................................53 11.4 HFS Office 2 – T11 - Tuesday and Wednesday……………......................................53 11.5 HFS Office 2 – T11 - Tuesday and Wednesday Peak Temperatures.........................54 11.6 HFS Office 2 – T11 Simplified Layers - Tuesday and Wednesday Peak Temperatures...........................................................54 11.7 HFS Office 2 – T11 Thermal Behaviour of 0C and 7C For Detailed and Simplified Models - .......................................................................55 11.8 HFS Office 2 – T11 Simplified Layers – Hourly Temperature Gradients Through 0C...............................................................56 11.9 HFS Office 2 – T11 Simplified Layers – Hourly Temperature Gradients Through 9C...............................................................56 11.10 IES Office 3 – General Temperature Profiles of Multiple Blocks in July.........................57 11.11 IES Office 3 – Typical Peak Temperature Profiles of Multiple Blocks……...................58 11.12 IES Office 3 – Hours of Over Heating for 25°C Threshold…….................................59 11.13 IES Office 3 – Hours of Over Heating for 26°C Threshold…….................................59 12.1 ECB Configuration Ideas for Future Research…………..…….........................................62

List of Tables 2.1 Physical Properties of T14 365 ..............................................................................05 5.1 Properties of Air at Atmospheric Pressure .........................................,........................17 5.2 Effective Conductivity of Air at Various Temperatures ..............,............................17 5.3 Material Properties Used in Computer Modelling ......................................................20 6.1 List of Equipment Used ..........................................................................................23 6.2 Test Cell Envelope and ECB Properties ..................................................................23 6.3 Radiative Heat Transfer Co-efficients ..................................................................23 6.4 Convective Heat Transfer Co-efficients ................................................................. 23 6.5 Heat Loss Through Each HC Wall ............................................................................. 23 6.6 Derivation of Air Change Rate ..............................................................................27 11.1 Concrete Block Properties ..........................................................................................51 12.1a Environmental savings for ECB 6C over medium weight concrete block walls per m2 wall system ..................................................................61 12.1b Environmental savings for ECB 4C over medium weight concrete block walls per m2 wall system ..................................................................61 12.2 Comparative Thicknesses of Concrete Block EPS Wall Systems ...............................63

Lisa Iszatt July 2007 Material Configuration vi

List of Symbols A Area (m2) c specific heat capacity (kJ/kgK) or (J/kgK) ρ Density (kg/m3) E Emissivity Factor (No Unit) g Acceleration due to gravity (m/s2)

!

Grx

Grashof Number (No Unit)

!

h or

!

hc Convective heat transfer coefficient (W/m2K)

!

hr Radiative heat transfer coefficient (W/m2K)

k Conductivity (W/mK)

!

ktotal

‘total conductivity’, representing heat transfer due to both conduction and convection (W/mK)

!

ke ‘effective conductivity’ due to convection (W/mK)

L Length or Height (m)

!

Nu Nusselt number (No Unit)

!

Pr Prandtl Number (No Unit) Q Power input (W) q Power generated within node (W) R Thermal Resistance (to conductivity) (m2 K/W)

!

Rcv

Resistance to ‘effective conductivity’ due to convection (m2 K/W)

β Thermal expansion coefficient (1/K) Ta1 Air temperature adjacent to ECB surface in hot chamber (°C) Ta2 Air temperature adjacent to ECB surface in cold chamber (°C) Tm1 Approximate mean radiant absolute temperature in hot chamber (°C) Tn1 Environmental temperature in hot chamber (°C) Tn2 Environmental temperature in cold chamber (°C) Tr1 Mean radiant temperature in hot chamber (°C) (Baffle Temperature) Ts1 Mean surface temperature of specimen in hot chamber (°C) Ts2 Mean surface temperature of specimen in cold chamber (°C) (T1 - T2) or ∆T Temperature difference (°C or K) U Thermal Transmittance (U-Value) (W/m2K) µ Absolute viscosity (kg/m.s or Pascal-seconds, Pa.s) ν Kinematic viscosity (m2/s) x Distance or Width (m) α Thermal diffusivity (m2/s)

List of Abbreviations

0C Zero Rows of Clay Added to Block CO2 Carbon Dioxide 9C Nine Rows of Clay Added to Block ECB Extruded Clay Block 0A5C Five Rows of Clay After Zero Rows of Clay

Added to Block EPS Expanded Polystyrene

1A8C Eight Rows of Clay After One Row of Clay Added to Block

IES Integrated Environmental Solutions- Virtual Environment Software Package

AC/h Air Changes Per Hour HFS Heat Flow Spreadheet CC Cold Chamber HC Hot Chamber

Lisa Iszatt July 2007 Material Configuration 1

1 Introduction 1.1 Background Global Issues Environmental degradation of Planet Earth is increasingly being accepted as a direct result of anthropological development. The rapid increase in greenhouse gasses and the corresponding temporal change in the last century is the most recognised and comprehensible indication of this link. This has been firmly substantiated by the Fourth Assessment Report Summary of the Intergovernmental Panel on Climate Change 2007, in which previously tentative predictions of catastrophic consequences are described as ‘almost certain’5. Carbon dioxide is one of the major greenhouse gasses, and since the industrial revolution atmospheric concentration has increased from 280 ppm to 379 ppm in 2005, and by 1.9ppm per year in the last 10 years. This significantly exceeds the natural range over previous the 650,000 years of 180 to 300 ppm6. Reducing CO2 emissions is an important factor in preventing run-away climate change, and countries ratifying the Kyoto protocol have set a series of reduction targets over the coming years. The Building Industry In the UK, as in most countries, the majority of our industries, services and transport rely on energy from burning fossil fuels, which pollute the environment. Renewable energy technologies can enable human development to continue whilst limiting ecological damage, but for this to be achieved, our energy requirements must also reduce significantly. The building industry is currently responsible for 50% of global carbon dioxide emissions7, and has been identified as an area where energy requirements and consequent pollution can be vastly reduced. CO2 emissions by the building industry occur during product manufacture and transport, construction and operation. There is often a conflict between reducing emissions at each of these stages. A balance must be struck between the embodied energy due to the manufacture and transport of a material and the energy that will be saved over the lifetime of a building due to the use of that material. It is widely argued that operational energy, particularly in high occupancy buildings, greatly outweighs embodied energy over the building’s lifetime8. The majority of operational energy savings result from reducing space-conditioning requirements, by creating a more stable thermal environment. Thermal Mass: Production and Performance A common example of this ‘energy payback’ is the use of concrete as thermal mass to regulate the temperatures of high occupancy buildings and thus lessen the cooling plant load. Unfortunately this equation does not take into account non-energy related ecological impacts of the material, including resource depletion, water use and toxin content. It also neglects to consider concrete’s inability to deconstruct or decompose, due to its nature as a compound and exacerbated by reinforcements and brittle binders. To account for all these factors and both current and future emissions, a low impact, well performing material would need to be specified.

5 & 6 IPCC (2007) 7 Roaf (2004, Pg5) 8 Webb (2007)


This thesis is concerned with reducing thermal conditioning requirements by using materials with comparatively low environmental impacts during production, to reduce emissions and other impacts noted above. An existing building product is identified and adjustments are made to affect its thermal performance. Specific configurations of thermal capacitance and resistance within the building material are evaluated with respect to their effects on temperature over time.

1.2 Overview In addition to the environmental impacts listed above, thermally massive materials, largely due to their density, tend to have a correspondingly high conductivity. This contributes to their ability to absorb heat and return it to the surface at a later time. This conductive ability leads to the loss of heat to the outside unless the material also has sufficient thermal resistance. To allow thermal coupling of the material with the heat carried by internal air, it is necessary to insulate on the external face of the material. Due to its exposure to the elements, this requires rigid insulation, which is generally environmentally less benign than softer insulation used in timber construction. Extruded Clay Blocks (ECBs) ECBs are a popular European building material, which due to their internal configuration are thermally resistant and do not require extra insulation to satisfy UK Building Regulations. They are classified as a thermally light to medium weight material, due to their low density. However, the internal matrix of clay and void gives the opportunity for thermal mass to be added in rows to the block. This thesis will investigate the use of clay powder to increase the thermal capacity of an ECB. It will use the existing matrix to experiment with various configurations of thermal capacitance and thermal resistance, using physical test cells, computer simulation, and heat flow calculations. The next three chapters describe ECBs, discuss existing orthodoxy concerning the use of thermal mass in buildings, and introduce the methodology. Subsequent chapters detail each experiment carried out. The final chapters compare the results obtained from each, and discuss potential practical applications. Limitations of the study are also considered and suggestions made for future research.


2 Extruded Clay Blocks (ECBs)

2.1 Introduction The ECB used in this study is the Thermoplan ZT14 Poroton produced by Ziegel in Germany, and supplied in the UK by Natural Building Technologies. ECBs have been used for over a century throughout Europe, due to their flexibility and efficiency. They are able to meet structural, thermal resistance, and fire protection requirements without additional reinforcement, insulation or chemical additives. ECBs also achieve a much more accurate tolerance in the vertical dimension than standard concrete blocks or bricks, allowing a thin bed mortar to be used of just a few millimetres instead of the standard 10mm mortar. The tongue and groove form on the sides negates the need for mortar between blocks on the same course. This greatly reduces material consumption and enables easier deconstruction and reuse.

2.2 Materials and Production Process Compared to concrete blocks, the ECB manufacturing process is less environmentally harmful, as firing temperatures are lower and there are no chemical additives bound into the finished material. Additives in concrete blocks account for a small percentage of the cement content and can include airing agents, water reducing agents, accelerators, retarders, water repellents and adhesive agents9. These remain compounded within the material long after its useful life, and there are issues with ground leaching at landfill. EBCs are still fired however, which requires energy and makes their decomposition extremely difficult, proven by the constant discovery of medieval clay building products, although the lack of chemicals additives does make this less of a problem. The ECB in question is fired to 1050°C, which is significantly lower than cement firing, at 2000°C10. This in turn signifies a reduction in emissions. Unfired clay and earth construction benefits from further reduced energy input (providing travel distances are kept to a minimum), and its ability to return, as found, to the ground. It also benefits from high thermal capacitance. Unfortunately it is currently difficult to specify unfired clay and earth products on a mass scale in low budget schemes, especially for public sector clients, due to the lack of commercial guarantees available. The ECB base material is raw clay, but secondary sacrificial materials are used to reduce the density. Either saw dust or polystyrene is mixed into the clay and extruded into one long block including perforations, which is cut to size and fired11. The choice of sacrificial material has a bearing on the environmental credentials of the finished block. Polystyrene produces a more efficient end product, but is more polluting when burned than saw dust. The porous nature, created by the sacrificial material in the extrusion and firing process, produces a lighter block and allows the wall to ‘breathe’. This allows less brittle renders to be

9 Berge (2000, Pg 97) 10 Berge (2000, Pg 98) 11 Albert Sommer of Ziegel (Telephone interview with Kristin Trommler – November 2006)


used, replacing cement with lime, which is fired to a lower temperature and is generally not enhanced with chemical additives. The production process reveals that ECBs are not perfectly benign. They are fired, sometimes with polluting secondary materials, which makes them more ecologically harmful than unfired clay products. Compared to concrete blocks however, which they are likely to compete with on a commercial level, there are many environmental benefits such as reusability, a reduced firing temperature, and lack of chemical additives. The integrated insulation and porous structure also reduces the need for, or impact of secondary materials.

2.3 Use in Construction ECBs can be used below ground but still require concrete strip foundations and a concrete or engineering brick plinth wall is often used. This is a standard requirement of masonry construction, and below ground concrete can only be significantly reduced by using framed construction methods. Laying the block is relatively simple. As discussed in 2.1, no mortar is required between blocks horizontally and very little is used between blocks vertically, due to the tongue and groove form and low vertical dimension tolerance. The thin bed mortar is easier to apply than cement mortar and can be rolled into place by machine to achieve an even spread, as shown in figure 2.1.

Blocks can be cut to form openings and angles. Although more care must be taken than with concrete blocks as the thermal and structural matrix must be retained. Chasing services into the inside face also affects thermal behaviour as the entire thickness of block contributes to insulative performance.

2.4 Use in the UK Although ECBs are a standard building product in Europe they are rarely used in the UK. Current suppliers import the blocks from the continent, mainly Germany or France, which increases the embodied energy of the material. It could however be argued that demand will lead to local production, which will reduce energy use in the long term, and provide healthy competition to the concrete industry.

In terms of cost, the materials and simplicity of construction would make ECBs a competitive option in principle. The relative youth of ECBs in the UK, does however drive up labour costs, as contractors attach a risk to working with unknown materials. There are few contractors in the UK with ECB building experience and some regions are not covered at all, leading to a lack of competitive pricing.

2.5 Configurations There are many types of ECB using different configurations, produced by various companies. Some examples are shown in figure 2.2. The partition blocks are much denser, as insulation does not need to be considered, and this leads to changes in the block’s internal pattern. The variety of 12 NBT (No Date-a)

Figure 2.1: ECBs on site: Thin bed mortar being applied between courses12


configurations introduces the possibility of varying the matrix to adjust thermal performance through the depth of external wall blocks. A denser layer to the inside would also allow a service chasing zone without compromising thermal resistance as discussed in 2.3.

Figure 2.2 Various Configuration Types for ECBs From NBT (No Date) except: *From Construction Resources (No Date), ** From Bouyer Leroux (No Date)

The thermal performance of ECBs is constantly being researched and improved upon. So far the best insulating block found by the author is the Thermoplan T11 by Ziegel, which achieves a U-Value of 0.29 W/m2K for a 365mm block. For experimental simplicity an early version of this block, the T14, has been chosen for its more regular clay and void matrix. This block is not as efficient an insulator, but can be modelled more easily in the simulation and equation based experiments. There is currently a version of the more efficient T11 block with the internal matrix of a T14 block in development in Germany. This block will be modelled for office scale scenarios.

2.6 ECB Physical Dimensions and Properties

Average Block Density 700 kg/m3 Thermal conductivity 0.14 W/mK U-value 0.35 W/m2K Heat Storage Capacity 255 kJ/m2K Specific Heat Capacity

(SHC) 1 kJ/kgK

Volumetric Heat Capacity (VHC)

700 kJ/m3K

248 m

m

365 mm

24

9 m

m

Table 2.1 (above): Physical properties of T14 36513 Figure 2.3 (left): Physical dimensions of T14 365

The key thermal properties of the Thermoplan T14 are given in table 2.1, and figure 2.4 gives comparative specific heat and volumetric heat capacities (SPC and VHC) for various heavy and 13 Ziegelwerk Klosterbeuren (No Date-b),


lightweight materials. It is shown that SPC does not vary a huge amount, but when density is factored in to give VHC, the range is much greater. ECBs are shown to have comparable values of VHC to softwood. The significance of thermal capacity is developed further in chapter 3.

Figure 2.5 Clay Added to ECB

Figure 2.4 Specific and Volumetric Heat Capacities for Various Materials *Adapted from Ziegel (No Date a) **Adapted from CIBSE guide A

Figure 2.6 Heat Transfer Mechanisms through ECB

2.7 Adjustments to ECBs

The layers of void throughout the ECB contribute to the thermal insulation due to the low conductivity of air. Convection currents within the voids also contribute to heat transfer through the block. To increase the thermal mass, clay powder will be added in layers to the block layer by layer, (figure 2.5). Figure 2.6 shows how heat transfer occurs through an existing ECB and through and ECB with three rows filled with clay powder. Chapter 5 describes these heat transfer mechanisms and the physical properties of air and clay in more detail. The ideal balance of clay and void will differ for different buildings according to heat load and orientation. Other factors affecting the performance of thermal mass will be detailed in the next chapter.


3 Thermal Mass 3.1 Thermal Capacitance and Thermal Resistance Thermal Capacitance refers to the material’s ability to store excessive heat energy when it is not needed and to release it when needed, or at a time when it can be dispersed more easily. In residential buildings, solar energy stored during the day is useful at night for space heating. In high occupancy buildings used primarily in daytime such as offices and schools, thermal mass is used to absorb casual internal heat gains from people or equipment, and is, similarly to a battery, discharged at night, ready for recharge the next day. This cooling process is often assisted by ventilation, described as night purging. A material’s ability to store heat is dependent on many factors due to the material and the surrounding environment including:

Material: Physical properties, Thermal properties, Density Surface colour (emissivity)

Physical dimensions Surface area, Depth

Environment: Location External/internal wall Ceiling Floor

Heat gains Direct Diffuse Remote

These will be discussed further in 3.4

Thermal Resistance is much easier to quantify. It refers to a material’s ability to resist heat flow through a specified thickness of a material, and is inversely proportional to the conductivity of the material.

3.2 Current Standards Standards for thermal resistance in buildings in the form of insulation have been written into the UK Building Regulations since their introduction in 1987, whereas thermal capacitance has only recently been acknowledged by the regulations as an important factor, due to the difficulty in quantifying the effects of thermal mass in buildings. The steady state equations used in SAP14 assessments disregard the effects of using thermally heavy or lightweight materials.15 The 2006 changes to ADPL16 require dynamic simulation to be used to predict energy use and CO2 emissions. Dynamic simulation considers all thermal properties of a material and models the effects of ventilation and temperature variations on these over time. ADPL also mentions thermal mass as a method of limiting overheating, but is still relatively ambiguous as to its appropriate use.

14 Standard Assessment Procedure: The Government's recommended system for energy rating of dwellings 15 Gilbert (2005) 16 Approved Document Part L of the Building Regulations


3.3 Benefits and Drawbacks of Thermal Mass The benefits of thermal mass in high occupancy buildings are clear, as it reduces the amount of cooling load required to keep the building temperature below a comfort threshold, and produces a lag between heat input and heat output that can be exploited diurnally. In temperate climate residential buildings, keeping the building warm and not cooling it down is the priority for most of the year, and thermal mass may not be appropriate. The increased length of time required raising the fabric of the building up to a comfortable temperature conflicts with the intermittent heating load resulting from modern occupancy patterns. The lag in temperature useful in high occupancy buildings has been found to waste energy in a domestic situation17. Another school of thought recommends that UK houses be designed for the Mediterranean climate predicted by the UKCIP0218 scenarios for the next century, and thermally massive buildings are identified as a way to deal with this passively19. Passive solar houses have used thermal mass for decades, exploiting direct solar radiation to store heat in the building fabric for use later. Investigations have been carried out in the last 50 years into the science of passive solar energy, and various conclusions have been drawn as to the best use of thermal mass.

3.4 Factors Affecting Thermal Mass Thermal mass is difficult to understand, and therefore difficult to design into a building. Various rules of thumb have been developed through experience, experimentation and by applying and adapting the laws of heat transfer. Some aspects of thermal mass design are easy to generalise. Surface colour, or emissivity, is important in allowing radiative heat to be transferred into the material in the first instance, and darker matt colours are most effective. A large surface area is also important but this must be balanced with its location. Other aspects are more difficult to generalise as being good or bad.

3.4.1 Physical Properties of the Material The Basic physical properties affecting thermal storage capabilities are:

C Specific heat capacity (J/kgK) ρ Density (kg/m3) K Conductivity (W/mK)

Specific heat capacity is the relationship of energy input to temperature change of a material, defined as the heat energy required raising the temperature of 1 kg of material by 1°. In practical terms, a material with a high SHC takes longer to raise its temperature and more heat energy is absorbed. Density refers to the ratio of mass and volume of a material. A material with a higher density would require a greater amount of energy per volume to raise its temperature. Volumetric Heat Capacity (J/m3K) is the product of SHC and density, and is more useful in determining a material’s thermal capacity. Conductivity describes the rate of heat transfer through a material. A higher conductivity allows heat to be transferred away from the surface and into the material more quickly. This keeps the

17 Eg: Baker and Steemers (1994); Isaacs and Donn (1994, Pg 26) 18 UKCIP (2002) 19 Bill Dunster Architects (2004)


internal face relatively cool and allows more heat to be transferred from the space into the material, improving the material’s performance as a thermal store. For the heat stored within the material to return to the room heat transfer in the opposite direction must occur. This could be brought on by a change in room air temperature or a change in conductivity deeper into the wall, for example by a separate layer of insulation.

3.4.1 Effective Depth of Thermal Mass: Rules of Thumb Existing orthodoxy implies that for thermal mass to be effective it must be in contact with or very close to the internal surface of the material. There are various theories as to the depth of effective thermal mass. It is clear that the effectiveness is dependent on the intensity of heat gain, but rules of thumb are often quite contradictory. Johnson states that for surfaces subject to direct solar radiation thicknesses of 20-30 cm are useful, whereas if the heat gain is diffuse, then larger areas of 10-15cm thick are more appropriate20. Mazria’s investigations found that for direct gain, depths greater than 8 inches gave little increased benefit, and that after 16 inches the difference was negligible21. Baker and Steemer, however, assert that for diurnal temperature cycles anything more than 5cm is ineffective22.

3.4.2 Effective Depth of Thermal Mass: Diurnal Heat Capacity Thermal mass on external walls has to be carefully balanced with thermal insulation to prevent loss of heat to the outside. Various equations have been developed by the passive solar house movement to help determine useful thicknesses of thermal mass. Balcomb derives the useful thickness of thermal mass from a material’s diurnal heat capacity (DHC). This is described as the daily amount of heat per unit of surface area and per degree of temperature swing that is stored and then given back to a room in a 24 hour period23. DHC is dependent upon specific heat capacity, density, conductivity, depth and the time period over which the heat is stored. Plotting DHC against thickness of various materials shows that a peak DHC is reached and that

after that point the return of heat back to the room is out of phase with the 24 hour cycle24. The result is that heat returns during the next cycle at a point when the wall is subject to heat gains. This decreases the temperature gradient between the air and the wall surface and therefore reduces its ability to conduct heat into the material. It will therefore be less effective as a thermal store. This is more important in some situations than others. In high occupancy buildings excess heat is not required at a later point, and generally needs to be dispersed half way through the cycle. A thickness

20 Johnson, 1992, Pg199 21 Mazria, 1979, Pg 137-140 22 Baker & Steemer, 1994 23&21 Johnson, 1981, pg143

Figure 3.1: Diurnal capacities of different materials (Plotted from data from Johnson, 1981, pg143)


past that at which the optimum DHC is achieved, will cause the periodity to be out of phase with the convenient discharge time, usually at night. This requires increased ventilation to cool the mass down to a point at which it can be recharged the following day. A natural diurnal drop in temperature will encourage the return of heat to the material surface anyway, but ensuring that the material is in phase with diurnal requirements, will enable this process to occur more efficiently. In a residential building where casual gains are not as high and the heat will at some point become useful again, the phase is not as crucial. Givoni introduces the idea of effective heat capacity EHC, which resembles DHC but takes long-term storage effects into account25. It draws on the solar load ratio model, which gives month by month estimates of building back up heat26, and consequently does not diminish at a specific thickness.

3.4.2 Location and Heat gains Location also has an effect on thermal capacity depending on exposure to heat gains and surface area. Thermal mass can be categorised as Primary, Secondary and Tertiary, according to whether it receives direct or indirect solar gains or if it is located remotely, receiving gains mainly via convection (from the room next door for example). Baker and Steemer approximate the relative effectiveness of mass types as shown in figure 3.2

There is debate as to whether the location of thermal mass in internal or external elements effects its DHC28. There are however clear benefits of using internal walls as thermal mass as they are generally subject to more direct solar gains and less interruptions in surface area, for example by windows. Another major benefit is that insulation need not be considered. This is shown by the configuration of internal ECB blocks in figure 2.2 which are much denser than ECBs used externally.

3.5 Summary There are many theories as to the effective positioning of thermal mass within a wall. It is generally agreed that the mass needs to be coupled with heat gains from the room and therefore needs to be very close to the inside face of the material. This thesis will test this orthodoxy and the effects of varying the position and depth of thermal mass throughout the block. The next chapter describes the methods used.

25 & 28 Givoni (1987, Pg 28) 26 Jones and Wray (1992, Pg185) 27 Approximated from Baker & Steemer (1994)

Proportional Areas Needed of Exposure to Types of Gain for Comparitive Thermal Mass Benefits

Primary

Secondary

Tertiary

Figure 3.2 Proportional Areas Needed of Exposure to Types of Gain for Comparative Thermal Mass Benefits27


4 Methodology

4.1 Introduction The aim of this thesis is to test the effects of varying the configuration of Thermal Capacitance and Thermal Resistance across an ECB. This Methodology will introduce and assess the tools used to test these configurations. The three methods used are a physical test cell (or hot box), computer simulation software, and a heat flow spreadsheet. Each will be described in more detail in the following chapters. The three experiments have varying levels of accuracy and areas of usefulness for understanding thermal behaviour. Physical test cells and computer simulations are often run in conjunction as comparison and validation. Physical test cells have the advantage of using real life materials whereas computer simulations use given physical and thermal data describing the material. Simplifications are made to describe the layers of material and any horizontal variation, for example joins are difficult to model. The advantage of computer simulation is that external factors influencing thermal behaviour such as infiltration due to test cell construction are minimised, and it is quicker to make adjustments to the model. It is however harder to identify where mistakes have been made in computer simulations. The transparency of physical testing can reduce this as each step is carried out at a slower pace and it is easier to follow the logic of the experiment. Conversely, the increased level of human interaction with the experiment can lead to increased opportunity for error. These various experimental pros and cons make validation between the two processes essential. For thermal analysis the major advantage of computer simulations over physical test cells is the speed at which real life scenarios can be modelled. Physical test cells are not scaled representations of a room, as thermodynamics is dependent on the dimensions of a space, and whereas the dimensions of a room can be scaled, thermal properties of a material can not. They are instead useful for comparing isolated thermal parameters to each other in a controlled environment. For this reason the experiments will be carried out first with physical test cells and the results validated by computer simulation. Computer simulation will then be used to simulate real life scenarios bearing in mind any potential inconsistencies that may have been identified between the two processes. As a further comparison, a mathematical model will then be used to assess heat transfer through various configurations of material. This will serve as a tool to validate and expand on patterns emerging from the other two experiments. One of the main limitations (similarly to the computer simulation) is that it relies on published properties of the materials involved, which may differ slightly to reality or be unexpectedly affected by other processes within the material. It also relies on a simplified geometry. The HFS, which has been calibrated with IES29, is more useful in describing heat transfer through the various layers of the ECB due to the detail of its graphical output. In this instance it will serve to explain, or contest, results obtained from the other two experiments.

29 Gilbert, 2005


4.2 Physical Test Cells As stated above, physical test cells are not scaled representations of a room. They are a controlled environment in which room conditions are simplified to test a specific aspect of thermal behaviour. They are useful for comparing one set of thermal properties with another set tested in near to identical conditions. Thermal tests can be executed externally to test real weather, using a set of identical external test cells simultaneously to ensure conditions are kept constant. This involves introducing an area of glazing to each cell to monitor the effects of solar gains over time. Thermal tests can also be carried out in a controlled internal environment. In this case a single cell can be set up and the experiment repeated for each variation, as thermal conditions can be kept constant and are not dependent on weather. These types of test cells are known as hot boxes and in laboratory conditions are used to determine approved thermal properties of materials. For this experiment the internal controlled hot box will be used, due mainly to the number of experiments that are required. It is also not essential to use real weather data as it is a behavioural comparison for given temperatures between configurations that is being examined, so a controlled heating profile is more useful in the first instance. The computer simulation, once calibrated to consider physical test cell results, will then be used in testing more realistic scenarios as they will be quicker to set up.

4.2.1 Method The test cell is constructed following the general principles set out by BS EN ISO 899030. It consists of hot and cold chambers either side of the ECB, in which a range of temperatures are measured. All physical properties of the wall materials are known. Steady state conditions are carried out initially and thermal transmittance results are compared to published and calculated data, to establish the degree of error. It is anticipated that there will be a large degree of inaccuracy in empirical thermal transmittance results, due mainly to the size of the sample and consequent surface perimeter to area ratio, but also to infiltration and inconsistencies in heat output from the lightbulb source. These areas of inaccuracy are discussed in detail in chapter 6. Dynamic heat transfer in the test cell is then tested by infilling voids with clay and testing each configuration. For experimental consistency this is simplified to a heat source being applied for 30 minutes and then thermal measurements taken throughout the test cell for the next 7.5 hours. The aim is to determine how effective each configuration is at moderating temperature extremes (thermal capacitance) while preventing heat flow through the block (thermal resistance).

4.3 Computer Simulation: IES The computer simulation software used is the IES Virtual Environment (VE) package. IES is an Integrated Environment, with a front end, Model Builder, that gives a visual interface to inputted data. The information is then analysed in separate interlinked software packages that use results obtained from each. This experiment will use Model builder to replicate the geometry of the physical test cell. Apache will then be used to model the thermal properties of the materials and the heating profile.

30 British Standard EN ISO 8990:1996 - Thermal Insulation – Determination of steady-state thermal transmission properties – Calibrated and guarded hot box (1996)


Model Builder represents each wall as a single line, which is given properties in Apache. Standard wall build-ups can be used, or created using the database of materials. It is also possible to modify and create new materials by setting data for U-Values, density and thickness, for example. The most challenging aspect of modelling an ECB in IES is dealing with the layers of clay and void. IES only allows a maximum of 10 layers of construction per material whereas an ECB has 51 layers including the voids. Modelling ECB solid elements and voids separately, only 4 void spaces can be represented within the 10 layers, after which an average value for thermal properties must be used for the remaining block. (The thermal values for each of these layers are derived from published data and heat flow calculations as described in chapter 5). The IES model is compared with the TC in this detail for the existing ECB and for the ECB with up to 4 layers of void filled with clay, both in steady state and dynamically heated conditions. The configurations 1 to 9 layers are then modelled using two simplified layers (an average for ECB solid element and clay powder, and an average for ECB and air void), and the results are compared. Infiltration and heat source errors derived from the test cell steady state calculations are entered as a single rate of heat loss in the IES models as infiltration.

4.4 Heat Flow Spreadsheet The Heat flow Spreadsheet developed by Gilbert31 uses a mathematical model in Microsoft Excel to predict heat flow through a material or combination of materials. Numerical approximations of equations describing the Physics of Heat Transfer are solved for a series of nodes across the material and the temperature of each node is calculated over a series of set time steps. Using conditional formatting in Excel to give temperature values a colour, a visual representation of 1- Dimensional dynamic heat flow is given. The spreadsheet is used in conjunction with the test cell and IES experiments as a further validation tool. It is also very useful for giving quicker results for each configuration so the limited number of tests that can be undertaken in the test cell (due to time) can be expanded upon. Its advantage over IES is the ability to measure each layer more accurately. It does however rely on average properties for each layer. As only one-dimensional heat transfer is being modelled, the clay bridges across the void layers need to be considered in these averages.

4.5 Summary All three tests are useful or accurate in different aspects of thermal analysis for this specific study. The above methodology is a starting point from which changes are made as experiments are undertaken, and opportunities and limitations arise. The order of testing is also indicative as results from all three experiments begin to inform each other.

31 Gilbert (2005) & Gilbert (No Date)


5 Process: Material Properties Analysis

5.1 Introduction For the IES and HFS models, values need to be derived for the individual materials, material layers and combinations of layers. For the existing ECB T14, data is obtained from thermal transmittance tests conducted in Germany using a 2.25m by 1.19m test wall. The resistance of the ECB wall was measured as 2.776 m2K/W32. In order to dissect this information into conductivity values for the individual materials, and average values for layers, the following steps were taken. 1 Calculation of Heat transfer through void spaces from first principles. (SECTION 5.2) 2 Approximation of surface resistance for the original data (using CIBSE guide A) 3 Calculation of conductivity of solid parts of the ECB T14 (figure 5.2) (SECTION 5.3) 4 Approximation of conductivity of clay (from data sheets and test cell results) 5 Calculation of total resistance for ECB in test cell 6 Calculation of average conductivity for void and clay layers 7 Calculation of layer combinations for simple models of each configuration (SECTION 5.4)

Summarised tables of material properties that were used in the

IES and HFS models are included at the end of this chapter.

5.2 Thermal Transfer Through Voids The primary source for the following method used is HOLMAN33, with validation by EARLAND. For temps 0 to 30 deg C, conductivity of air, k is in the range 0.0241 - 0.0265 W/mK. A constant value of k = 0.026 W/mK has been assumed for this experiment. The margin of error as the temperature changes is considered minimal compared to other variables in the experiment. As there are air gaps in the ECB, heat transfer by convection must also be considered. Convection is more complicated as it incorporates fluid dynamics, and must be considered in two dimensions. Resistance to convection is normally calculated by the equation:

!

Rcv

=1

h [1]

Where h is the convective heat transfer coefficient, and is generally derived by experiment. For simplification heat transfer by convection is considered as effective conduction,

!

ke. The

resistance to effective conduction is defined by the equation

!

Rcv

="x

ke

[2]

For total conduction through the void the following equation is used 32 Gesellechaft für Qualitätssicherung und Materialprüfung mbH, (1998, pg 3) 33 Holman (2002, Chapter 7)


!

ktotal

= k + ke [3]

!

ktotal

Is ‘total conductivity’, representing heat transfer due to both conduction and convection (W/mK)

!

k Is conductivity due to conduction (W/mK)

Where

!

ke Is ‘effective conductivity’ due to convection (W/mK)

5.2.1 Derivation of Effective Conduction The derivation of ke is calculated using dimensionless numbers, which are derived empirically, and can be used for a known and limited set of circumstances. These are used to simplify predictions of heat transfer by convection. Grashof Number Approximates the ratio of the buoyancy to viscous force acting on a fluid and is defined by the equation

!

Grx ="2g# T

1$T

2( )x 3

µ2 [4]

ρ Is density (kg/m3) g is acceleration due to gravity in (m/s2) β is the thermal expansion coefficient (1/K) (T1 - T2) is temperature difference (°C) x is distance (m)

Where

µ is absolute viscosity (kg/m.s or Pascal-seconds, Pa.s) The thermal expansion coefficient can be calculated by the change in volume and density of a substance during heat transfer at a constant pressure, and is defined by the equation

!

" =1

V

#V

#T

$

% &

'

( ) P

= *1

+

#+

#T

$

% &

'

( ) P

[5]

For gases the volume V is approximately proportional to the absolute temperature T, hence this is simplified to

!

" =1

T [6]

Prandtl Number The Prandtl number is used in the study of forced and free convection, and is given by

k

cPr

µ= [7]

Where c is the specific heat capacity (kJ/kgK) Nusselt Number The Nusselt number is used to approximate the difference between actual heat transfer observed in reality and that predicted by conduction alone, and is defined by


!

Nu "ke

k [8]

Combining [8] with [1] and [2] gives

!

Nu =hx

k or

!

h = Nuk

x [9]

Combining Grashof, Prandtl and Nusselt Numbers to Approximate Effective Conduction Through experimentation the following relationship between the Grashof, Prandtl and Nusselt numbers has been established

!

Nu = C(GrxPr)

n L

x

"

# $ %

& '

m

[10]

C = 0.197 n = 1/4 m = -1/9

Empirical relations for free convection in enclosures for a defined set of scenarios34

Where

L is height (m) Combining [8] with [10] gives

!

ke

k= C(Gr

xPr)

n L

x

"

# $ %

& '

m

[11]

Equation [11] can now be used to calculate heat transfer by convection.

5.2.2 Effective Conduction for Average Temperatures

Properties of air at atmospheric pressure

0.5

1

1.5

2

2.5

3

3.5

-73.15 -23.15 26.85 76.85

Temperature deg C

Va

rio

us

un

its

(s

ee

le

ge

nd

)

!

c

µ

k

where ρ is density (kg/m3) c Is specific heat

capacity (kJ/kgK) µ is absolute viscosity

x 105 (kg/m.s) k is conductivity x 102

(W/mK)

Figure 5.1 Properties of air at atmospheric pressure35 34 Holman (2002, Pg 338) 35 Plotted from Holman (2002, Pg 602)


Before determining a value for effective conduction it is important to consider that material properties of air vary with temperature. As expansion of [11] reveals, effective conduction is dependent on many of these properties, which could cause accumulative inaccuracy over a large temperature range. Figure 5.2 plots various material properties of air.

Table 5.1 lists values derived from the figures used to plot the graph in figure 5.2, for the material properties of air at 0°C, 20°C and 30°C. The values are used to calculate effective conduction at these temperatures to determine whether this will be a significant factor in heat flow calculations.

Rearranging [11] with the appropriate empirical relations for free convection in enclosures36 gives

!

ke

= 0.197 " Grx"Pr( )

14L

x

#

$ % &

' (

)19

*

+ , ,

-

. / / " k [15]

Table 5.2 shows that

!

ke varies only marginally between

0°C and 30°C. A value of

!

ke = 0.01 W/mK is taken as an appropriate level

of accuracy for this experiment.

Using a value of k=0.026 W/mK for conduction as discussed at the beginning of this section, the following total value for heat transfer through the ECB voids is derived.

!

ktotal

= 0.026 +0.01 = 0.036 W/mK

This corresponds well with rules of thumb used to approximate heat transfer through voids37.

5.3 Derivation of ECB Solid Element Properties Density and specific heat capacity are given for the solid parts of the ECB block, by Ziegel data sheets38. For conductivity, the fractional resistances of section types through the ECB were calculated, (see figure 5.2) using assumed surface resistances from CIBSE standard tables. Conductivity values for ECB solid were inputted and iterated until the total resistance matched published data. Calculated conductivities are 0.087 and 0.539 W/mK respectively for T14 and T11 solid elements.

36 Holman (2002, Pg 338) 37 Earland (2007) 38 Gesellechaft für Qualitätssicherung und Materialprüfung mbH ,(1998, pg 3)

Tem

pera

ture

ρ de

nsity

c sp

ecifi

c he

at

capa

city

µ ab

solu

te

visc

osity

x 1

05

k co

nduc

tivity

T/°C (kg/m3) (kJ/kgK) (kg/m.s) (W/mK) 0 1.304 1.0055 1.713 0.0241 20 1.21 1.0057 1.812 0.0257 30 1.166 1.006 1.861 0.0265

Table 5.1 Properties of air at atmospheric pressure.

T 0°C 20°C 30°C Grx 152.079 109.025 92.806 Pr 0.715 0.709 0.706

!

ke 0.0106 0.0104 0.0103

Table 5.2 Effective conductivity of air at various temperatures (Various Units – See Figure 5.1)


Red indicates extent of each section type Excel Spreadsheet Fractional

Area (%) Resistance

(m2 K/W)

TYP

E 1

0.804 6.411 TY

PE

2

0.025 3.296

TYP

E 3

0.025 3.056

TYP

E 4

0.012 5.932

TYP

E 5

0.025 0.420

TYP

E 6

0.075 0.420

TYP

E 7

a &

7b

0.033 1.884

TYP

E 7

b

Condensed version of each part of excel spreadsheet used for section types. Y

ellow = void. G

rey = solid EC

B.

0.0004 6.909

Figure 5.2 Derivation of thermal conductivity for ECB solid elements

5.4 Derivation of Layer Properties For IES and HFS Models The average material properties for layers across the block differ according to whether the block is analysed individually, as in the test cell (figure 5.3), or in series, as in a wall (figure 5.4). Due to the conductivity occurring at the edges. For the single block in the test cell the tongue and groove edges are considered as isolated by the EPS walls, and therefore resisting heat flow from the hot to cold chamber. This is a simplification, as heat flow does not only occur in one dimension, but it is also the level of detail


that would be considered by the calculations in the simulations used. For the ECBs in series, the tongue and grooves are simplified to rectangles for analysis of material layers through this section type. A gap of 1mm is modelled as tolerance where the tongue and grooves do not quite meet. It is observed that the gap allowed at this point has a noticeable effect on the total resistance of the ECB wall.

Figure 5.3 Assumed Extent of 1D Heat Flow Through Single ECB

Figure 5.4 Assumed Extent of 1D Heat Flow Through ECB in Series

For the T14 and T11 blocks the following need to be established.

1. Calculation of total resistance of ECB (for a single block and in series) 2. Calculation of conductivity for average void layer 3. Calculation of conductivity for average clay layer 4. Calculation of layer combinations for simple model of each configuration

The values for clay were taken from CIBSE data sheets39. This listed various clay based building materials, of which clay pavoirs were selected due to the similarity in density measurement to those tested and physical test cell observations, (although only an approximation could be derived from these as is discussed in chapter 6). For the average clay and void layers a similar spreadsheet to that illustrated in figure 5.2 was used to find fractional resistances and then average conductivities for each row. The density and specific heat capacity values are derived from a fractional percentage of each material in the layer according to volume. For calculation of average layer combinations an average conductivity value is calculated from the total resistance of a number of simplified layers. The density and specific heat capacity values are again derived from a fractional percentage volume of each layer.

5.5 Summary The final values used in the IES and HFS models are summarised in table 5.3 below. When entering material properties into computer based simulations there are feasible inaccuracies due to human error and original data inaccuracy. These are increased for a complex material such as an ECB due to the number of steps and the quantity of data needed.

39 CIBSE (1999)


Table 5.3 Material Properties used in computer modelling

T11

T14

CLAY

AIR

Co

nd

ucti

vit

y

(W/m

K)

0.5

39

0.8

70

1.8

00

0.0

36

Den

sit

y

(kg

/m3)

1430.0

00

1430.0

00

1500.0

00

1.3

00

SH

C(J

/kg

K)

998.0

00

998.0

00

840.0

00

1006.0

00

AV

ER

AG

E M

AT

ER

IAL

LA

YE

RS

AV

ER

AG

E C

OM

BIN

AT

ION

LA

YE

RS

CLAY L

AYER

1

CLAY L

AYER

2

VO

ID

LAYER

1

VO

ID

LAYER

2O

C1C

2C

3C

4C

5C

6C

7C

8C

9C

LAYER 1

LAYER 1

LAYER 2

LAYER 1

LAYER 2

LAYER 1

LAYER 2

LAYER 1

LAYER 2

LAYER 1

LAYER 2

LAYER 1

LAYER 2

LAYER 1

LAYER 2

LAYER 1

LAYER 2

LAYER 1

LAYER 2

Th

ickn

ess

(m)

0.3

65

0.0

24

0.3

41

0.0

38

0.3

27

0.0

52

0.3

13

0.0

66

0.2

99

0.0

80

0.2

85

0.0

94

0.2

71

0.1

08

0.2

57

0.1

22

0.2

43

0.1

36

0.2

29

Co

nd

ucti

vit

y

(W/m

K)

1.6

44

1.6

80

0.1

14

0.0

93

Co

nd

ucti

vit

y

(W/m

K)

0.1

44

1.0

56

0.1

40

1.1

24

0.1

40

1.1

58

0.1

40

1.1

78

0.1

40

1.1

92

0.1

40

1.2

02

0.1

41

1.2

09

0.1

41

1.2

15

0.1

41

1.2

19

0.1

41

Den

sit

y

(kg

/m3)

1488.2

33

1490.9

48

241.4

69

186.0

46

Den

sit

y

(kg

/m3)

665.9

12

1451.8

37

643.5

03

1458.2

27

644.0

68

1461.1

76

644.6

83

1462.8

74

645.3

56

1463.9

78

646.0

95

1464.7

53

646.9

10

1465.3

27

647.8

14

1465.7

69

648.8

22

1466.1

20

649.9

54

SH

C(J

/kg

K)

840.0

00

840.0

00

978.0

95

984.5

34

SH

C(J

/kg

K)

925.1

27

840.0

00

927.4

74

840.0

00

927.4

18

840.0

00

927.3

57

840.0

00

927.2

91

840.0

00

927.2

18

840.0

00

927.1

37

840.0

00

927.0

48

840.0

00

926.9

49

840.0

00

926.8

37

Resis

tan

ce

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T11 - MULTIT14 - SINGLE T14 - MULTI


6 Process: Test Cell 6.1 Introduction The test cell used was a hot box, for reasons discussed in 4.2. The hot box is a controlled environment, to keep the conditions as similar as possible for each configuration.

6.2 Set Up

Figure 6.1 Exploded view of test cell set up The Test cell was set up as in figure 6.1. The dimensions of the hot chamber and cold chamber measured approximately 0.25m x 0.25m x 0.25m each. The external walls consisted of two layers of 60mm EPS, staggered to improve air tightness, with a layer of matt black painted cartridge paper to the inside. The thermocouples and lightbulb lead were fed through holes in the upper face of the test cell, which remained fixed in place. The holes were then filled with sealant and covered with gaffer tape on the external face. The thermocouple in the middle of the block was fed through a cylindrical cut out of the upper EPS face and fixed to a pencil for stiffness, and to ensure that it did not touch the clay edges. This was then fed into the centre of the block for each configuration. The cylindrical cut out was wrapped in a layer of carpet underlay foam for air tightness. Figure 6.2 shows other air tightness measures taken. The front face of the test cell was unfixed. This was kept as two separate layers enabling taping around the edges of each. Sealant was used wherever elements were fixed. The tongue and groove edges of the ECB were filled with EPS strips and the block was then wrapped in a double layer of carpet underlay foam on four


sides to form a buffer to infiltration around the edges. This also made it easier to remove after each experiment. The thermocouples were used to measure temperature throughout the test cell. This information was read by the data logger and fed into the laptop as shown in figure 6.3.

Figure 6.2: Plan view of test cell set up

Figure 6.3: Section through test cell set up


6.3 Equipment

A list of equipment used is given in table 6.1 and each are described further in the following sections.

6.3.1 Test Cell Envelope: Material Properties

Material Thermal Conductivity (W/mK) Thickness (m) Source

Expanded Polystyrene (EPS) 0.035 0.12 CIBSE

Cartridge Paper Painted Matt Black 0.06 0.0005 CIBSE

ECB T14 0.146 0.365 Ziegel (eliminating assumed surface resistance)

Table 6.2 Test cell envelope and ECB properties The properties of the test cell envelope and ECB T14 are given in table 6.2. The U-Values for each wall of the hot chamber were calculated using the above information and standard values for surface resistance. The values used were defined by the equation below, using the data in tables 6.3 and 6.4.

1 1 Rs =

6/5Ehr + hc Rs = Ehr + hc

Internal surface resistance External surface resistance

Where E Is the emissivity factor of specimen surface (Typically 0.9) hr Is the radiative heat transfer co-efficient (W/m2K) hc Is the convective heat transfer co-efficient (W/m2K)

40 & 25 CIBSE Guide A

Test Cell Envelope Expanded polystyrene (EPS) Cartridge paper painted matt black Gaffer tape / Sealant Apparatus: Data logger 25W, 5W and 2W light bulbs and leads Wattage and current meter Sheet metal (as a radiation barrier) Materials ECB T14 (as described earlier) Clay powder (for filling the ECB incrementally)

Table 6.1 List of Equipment Used

Mean Temp of Surfaces hr Direction of heat transfer hc Hot Chamber wall U-Value

(W/m2K) Heat loss through

wall* (% total) 0 4.6 Horizontal 2.5 ECB 0.3633 19.1

10 5.1 Upwards 5.0 EPS Horiz 0.3072 16.2 20 5.7 Downwards 0.7 EPS Horiz 0.3072 16.2

EPS Horiz 0.3072 16.2

Table 6.4 Convective heat transfer co-efficients (W/m2K) 41 EPS Up 0.3059 16.1

Table 6.3 Radiative heat transfer co-efficients (W/m2K) 40

EPS Down 0.3074 16.2 Table 6.5 Heat loss through each HC wall

*(When cold chamber = external air temperature)


Table 6.5 gives assumed U-Values for hot chamber walls and the percentage heat loss expected through each wall given equal cold chamber and external temperatures. These were adjusted according to measured temperature differences.

6.3.2 Apparatus Data logger and thermocouples The data logger used is the Pico TC-08 Thermocouple Data Logger. This takes readings from 8 thermocouples (TCs) simultaneously. The thermocouples used are K Type Exposed Wire with a fibreglass coat, which can be used to record temperatures in the range -60°C to 350°C. The data logger runs directly from a PC and is capable of taking 4 readings per second from each thermocouple. The data can be analysed whilst being recorded both numerically and graphically. It is also possible to set up certain calculated parameters, which enable equations based on input temperatures from thermocouples to be continually updated whilst the experiment is in progress. This gives the user an overview of the results, allowing errors to be spotted early. Alarms can be set for each parameter (input from thermocouples or calculated parameters) so that the power input can be switched on and off at specific temperatures, allowing continuity between experiments. The calculated parameters used are described in 6.3.1 The light bulbs used were:

- 25W, 240V, GLS Incandescent - 5W, 12V Tungsten Halogen - 2W, 12V Lilliput LED

The wattage and current meter displays the power consumption of an appliance, and was used to monitor the power input via the light bulb to the hot chamber.

Figure 6.4 Photos of Equipment The radiation barrier was used to ensure an even spread of radiative heat to the ECB surface, to avoid heat being concentrated towards a point on the surface. A sheet of aluminium was used for this purpose, and painted black on the front surface to minimise reflective radiation to the ECB surface (see figure 6.4, bottom right). The back of the barrier was left unpainted, to reflect heat to


the back of the hot chamber onto the black paper surface of the external walls. This also helped to eliminate direct radiation to the ECB surface.

6.3.3 Added Material: Clay Powder

The clay used was Scarva Earthstone Architectural Clay. This was air dried for 48 hours before being ground to powder form. Power was used rather than wet clay, as the water content would have been difficult to keep constant. Wet clay would have a higher specific heat capacity increasing its thermal mass to varying degrees, which would affect the thermal performance measured.

6.4 Method The thermocouples were placed throughout the test cell and in the external air as set out in figure 5.6. The light bulb was switched on and the temperatures recorded by each logger. Various heat inputs were tested. The ECB was brought to a steady state with a 5W bulb (average power consumption 4.5W), which took approximately 13.5 hours. The data readings were observed, and steady state was defined as all temperature readings varying less than 0.05 degrees over a period of 1000 seconds. The average temperatures were taken over this period to calculate the U-Value. This was compared to the known U-Value, to determine the accuracy of the test cell, and derive a value for infiltration heat loss and other errors. From this an air change rate was calculated for use in further configurations and in the IES and HFS models.

Figure 6.6 Thermocouple positions through block

6.5 Calculations This section describes the calculations used to determine thermal transmittance through the existing block, for calibration with published figures. In larger scale tests, surface resistance and

Figure 6.5 ECB and Clay Powder


coefficients for radiation and convection heat transfer can also be determined, which could be used for IES computer simulation and heat flow spreadsheet models. It was discovered however, that the level of inaccuracy due to the size of the test cell made this very difficult, and values from standard tables (figures 5.2 and 5.3) were used instead. The following data was used to determine a value for thermal transmittance (U-Value)42.

Defined parameters Q Power input Average 4.5W A Metered area (specimen surface) 0.0625m2 E Emissivity factor of specimen surface Assumed 0.9 Measured parameters Ta1 Air temperature adjacent to ECB surface in hot

chamber (°C) Thermocouple 4

Tr1 Mean radiant temperature in hot chamber (°C) (Baffle Temperature)

Thermocouple 3

Ts1 Mean surface temperature of specimen in hot chamber (°C)

Thermocouple 5

Ta2 Air temperature adjacent to ECB surface in cold chamber (°C)

Thermocouple 8

Ts2 Mean surface temperature of specimen in cold chamber (°C)

Thermocouple 7

Single values are taken for the temperature values listed above due to the limited size of experiment and number of thermocouples available. In an experiment with a larger metered area and chamber volume it would be necessary to take averages, as these values would vary more considerably. The mean radiant temperature, refers to the radiant temperature seen by the specimen, and in this instance is measured as the mean baffle temperature, specimen side. As the other surfaces are painted black and thus their reflective ability reduced, radiation from these surfaces to the specimen surface is assumed to be negligible. This is also due to the narrow angle of wall surface seen by the specimen surface. Calculated parameters Tm1 Approximate mean radiant absolute temperature in hot

chamber (°C)

Tm ≈ (Tr1 + Ts1)/2

hr1 Radiation coefficient in hot chamber (W/m2K) hr = 4σ Tm

Where σ is Stephan’s constant [5.67x10-8 (W/m2K4)] Tn1 = Ts1(Q/A)+Ehr (Ta1-Tr1).Ts1 Tn1 Environmental temperature in hot chamber (°C) (Q/A)+Ehr (Ta1-Tr1)

Tn2 Environmental temperature in cold chamber (°C) Tn2 = Ta2 Through initial testing it was observed that the environmental temperature approximated the air temperature adjacent to the ECB within an error factor of 0.01 degrees. For the cold chamber it was therefore decided that the air temperature would be used to represent environmental temperature. From the above parameters the U-Value can be calculated: U Thermal transmittance of specimen (W/m2K) U = Q A (Tn1-Tn2)

42 Method from BS EN ISO 8990:1996


Infiltration losses and Air Change Rates To determine an infiltration rate for the test cell a spread sheet was set up to analyse the measured data. Table 6.6 gives an overview of the method used.

SURFACE U-VALUE (W/m2K)

Q (W) % Q Q IDEAL

(W) Q INFIL LOSSES

(W) AIRCHANGES

(AC/h)

ECB 0.3633 0.501 17.293 0.778 0.277 2.2

EPS Horiz 0.3072 0.479 16.553 0.745 0.265 1.9

EPS Horiz 0.3072 0.479 16.553 0.745 0.265 1.9

EPS Horiz 0.3072 0.479 16.553 0.745 0.265 1.9

EPS Up 0.3059 0.477 16.483 0.742 0.264 1.9

EPS Down 0.3074 0.480 16.564 0.745 0.266 1.9

TOTALS 2.897 100 4.5 1.603 11.6

Table 6.6: Derivation of Air Change Rate The U-Values for each wall are as given in table 6.4 and heat transfer through each wall (Q) is given by the equation Q = UA (Tn1-Tn2) Where U is the known U-Value (W/m2K) A Is the surface area m2 Tn1-Tn2 is the temperature difference Degrees C or K The temperature difference between hot and cold sides of the ECB is defined above. For the temperature difference between the hot and cold sides of the external test cell walls, the temperature at the back of the hot chamber (thermocouple 2) and the external temperature (thermocouple 1) were used. For the external reading, the temperature difference around the hot chamber side of the test cell was measured at various points throughout the experiment, and was found not to vary by more than 0.2 degrees around the average. This was varied in the spreadsheet and found to affect the resultant air change rate by 0.1 AC/hour maximum. The temperature was assumed constant, and the air change rates for each external wall were therefore taken as averages of total infiltration through the external fabric. The percentage heat flow through each wall was calculated from the heat flow for each element and the total heat flow through all of the elements. Q Ideal, is the heat flow through each element given the percentages from column 3, and assuming no infiltration. Infiltration losses are calculated as the difference between ideal and actual heat flow. The number of air changes per hour are calculated by the following formula AC/h = Qlosses 3600ρcV(Tn1-Tn2) where Qlosses is infiltration losses (W) ρ Is the density of air (assumed 1.3 kg/m3) c Is the specific heat capacity of air (assumed 1006 J/kgK) V Is the volume of the hot chamber (approximately 0.0156m3) Tn1-Tn2 is the temperature difference Degrees C or K


The measured infiltration rate was 11.6 AC/h on average. This is extremely high. Steady state tests were also performed with the 25W and the 2W bulb, but it was found that this degree of inaccuracy remained. The next section describes assumptions and inaccuracies that will have affected this result.

6.6 Assumptions and Inaccuracies British Standard EN ISO 8990:199643 has been used for guidance on hot box design. British Standards are used to regulate the empirical derivation of thermal transmission properties of materials, generally U-Values, and as such is onerous in their requirements. As the point of this experiment is not to determine specific thermal properties, but to compare the results of adjustments with each other this level of detail is less essential. However, it is important to consider the effects of an increased thermal capacity on thermal transmittance as a comparison between configurations, and so a reasonably accurate reading is useful. In laboratory conditions where thermal properties are to be determined, inaccuracies occur due to equipment design, calibration and operation and specimen properties. Specimen properties include example thickness, thermal resistance and homogeneity. The details that have necessarily been simplified or omitted will be considered as limitations.

6.6.1 Hot Box Design

Figure 6.7 Hot box construction

43 British Standard EN ISO 8990:1996 (1996) Thermal insulation - Determination of steady-state thermal transmission properties - Calibrated and guarded hot box


The following specifications were designed according to BS EN ISO 8990:1996

- The hot box was designed around for the material to be tested

- Cold side chamber was designed to the same size and emissivity as the hot side.

- The walls were made as air and vapour tight,(figure 6.7), and as thermally uniform as possible

- Depth of chamber was restricted to a size suitable to fit all equipment

- Hot spots on the surface were minimised by the use of a baffle. This shielded the ECB from direct radiation from the bulb, to give a more even surface temperature, (Figure 6.8). This was also minimised by the low emissivity of the external wall surfaces.

Figure 6.8 Heat Transfer Mechanisms in Hot Chamber

The following limitations were identified It became apparent that the size was a significant limitation. The surface area of the ECB used in this experiment, 0.25 x 0.25m, is 1/6th of the BS recommendation of 1.5 x 1.5m. The resultant inaccuracy is due to the fact that surface coefficients will not be uniform, especially close to the borders of the test cell. The ratio of metered area to perimeter of meter area should also be reduced ideally, because 1 dimensional heat transfer will not be retained at perimeter, and will not form part of the calculations of heat transfer through each wall.

Figure 6.9 Heat transfer and infiltration through test cell

It is also recommended that heat transfer through walls should not exceed 10% of total heat energy transfer. The heat flow through the external envelope was calculated as approximately


81%. This can however be quantified by initial tests and factored into final calculations as a known imbalance. In laboratory conditions it is expected that the equipment used undertakes performance calibration and that all thermocouples are checked before each experiment. Reaction testing was conducted on each thermocouple before experiments (testing that each was reacting to being held for a few seconds and that temperature readings were the approximately the same between thermocouples), but more detailed testing would be beneficial. Complementary measurements of other materials in the test cell would also have been useful. For instance, the testing of a sample of the EPS used for the hot box external walls would have helped to assess the infiltration rate calculated by ECB steady state tests.

6.7 Summary The hot box constructed is a useful tool in measuring the effects of changes to the ECB with respect to temperature over time. There are however limitations, which are mainly a result of the small size of test cell and the consequent ratio of edges to surface area. The infiltration levels tested are very high, but are presumed to be mainly due to diagonal heat transfer occurring, which are not factored into the one-dimensional calculations used to analyse the readings.


7 Process: IES Simulation

7.1 Introduction IES was used to simulate the thermal behaviour of various sizes of space, levels of heat gains and ventilation strategies, for different ECB configurations and examples of concrete block wall systems.

7.2 Test Cell Calibration Set Up

For calibration with the test cell the set up was modelled as in figure 7.1. The hot chamber was set up as a room surrounded by buffer zones fixed at 22°C (by adding heating and cooling systems around the same set point). The external walls of the buffer zone were set as 5m of EPS. The partition walls between the hot chamber and buffer zone were set as 120mm EPS and 1mm of black painted paper to match the test cell. The ECB wall was modelled as an external wall to the sheltered zone within the buffer zone. The heat input was supplied by casual gains due to lighting, set to the same power rate as the test cell. Infiltration was fixed at 11.6 AC/h.

Figure 7.1 IES:Test Cell Calibration Set Up Multiple models were set up as in figure 7.2, and the ECB wall was adjusted for each. Two methods of modelling the configurations of ECB were employed. The first four configurations were modelled with 10 layers, as this was the maximum allowed by IES. This was achieved by modelling four void or clay layers between ECB layers, and then taking an average value for thermal properties for the remaining block.

The configurations 1 to 9 layers were then modelled using two simplified layers (an average for ECB solid element and clay powder, and an average for ECB and air void). The results were compared.

Figure 7.2 IES: Multiple Test Cell View


7.3 Buffered T14 Office This model was set up to test the difference in temperature predictions delivered by the modelling methods described above. The original model was scaled up to 16 square meter floor area and a 2.5m floor to ceiling height. Heat gains were set to 90 W/m2 to represent a high-density modular office44, and the infiltration rate was set at 5 AC/h as a standard ventilation level requirement for office spaces 45. This office was simplified to one external wall, with other surfaces joining a buffer zone. No windows were included, so that internal gains were considered in isolation.

7.4 Semi Buffered T11 Office

This office was set up to match the conditions modelled in the HFS, represented in figure 7.3. This assumes that every external element is a perfect insulator except one monitored wall. The internal heat gains and the ventilation strategy were kept the same as the buffered T14 office. For this experiment the original ECB, up to the ECB filled with 9 layers of clay were tested along with 4 types of concrete block wall construction: Heavy weight, medium weight, lightweight and aerated. IES and HFS results were also compared.

Figure 7.3 IES: Semi Buffered Office Diagram

7.5 Stand-Alone T11 Office For this model the floor area was increased to 240 square meters, and the floor to ceiling height to 3m. All external walls were set to the same material for each configuration. For this experiment more variations of concrete block were tested based on real examples. The casual heating gains were reduced to 60 W/m2 to represent a high density office of this scale (accounting for circulation and core areas). The ventilation was kept to 5 AC/h during the day and 2 AC/h was added for night purging. No windows or doors were added, so solar gains were not considered. Comparative peak temperatures and hours of over heating during the month of July were measured for each model.

7.6 Limitations of the IES Models IES gives a simplified interpretation of the conditions in a building, or room. It is set up to understand elements such as wall, floor and roof, and as such is not ideal for representing very small scale scenarios, such as the test cell. IES has trouble interpreting the effects of putting two rooms inside another room, as is the simulated translation of the physical test cell set up. The effects of the outer room did not prevent the inner rooms from being effected by external weather data. It is possible to adjust the weather

44 Knight and Dunn (No Date) 45 McMullan, (2002, Pg 94)


data in IES to read as a constant temperature (to simulate indoor conditions) by adapting and importing external weather files, but this could not be achieved in the time available. Instead several individual buffer rooms were set up that surrounded the hot chamber, which appeared to shield it from the effects of the weather data. It is unclear however, how much the internal temperature was affected by its surroundings, and the environmental conditioning of the buffer zone may have reduced the effect of heat generated within the hot chamber, for the initial models.


8 Process: Heat Flow Spreadsheet

8.1 Introduction The Heat flow Spreadsheet (HFS) developed by Gilbert 46 is used as further analysis to the results obtained from the physical and simulated tests. Section 8.2 explains the mathematic background to the original spreadsheet and section 8.3 explains methods used and modifications made to represent the conditions modelled in test cell and IES experiments. This includes adaptations to deal with the increased layers of material and the addition of very simplified weather data. Section 8.4 discusses the limitations of the models created.

8.2 Mathematical Background of Existing HFS As explained in chapter 4, the HFS uses Microsoft Excel to predict heat flow through a material or combination of materials. Equations derived from Heat Transfer equations were entered into excel and solved for nodes across the material. The temperature of each node is calculated over a series of set time steps. Using conditional formatting in Excel to give temperature values a colour, results in a visual representation of 1- Dimensional dynamic heat flow over time.

Figure 8.1 HFS: Position of nodes through ECB The ECB is simplified into nodes as shown in figure 8.1. The red circles represent the nodes and the smaller black circles represent a material change. The first and last nodes are on the internal and external faces of the wall, and nodes in between are placed centrally in each material layer. For each node the resistance of both materials is calculated from the conductivity and the distances shown in the first row of figure 8.1, and the total used for inter-nodal resistance.

46 Gilbert (2005)


Figure 8.2 HFS: Spreadsheet set up in excel

All of the material properties are entered at the top of the spreadsheet, broken down into nodal data and inter-nodal data. The coloured stripes across the top of the sheet represent ECB solid element (cream), clay (brown) and air (grey). These are copied across when changes are made to each model and the calculations in the dependent cells update accordingly. This takes a long time for complicated spreadsheets. The seconds between time steps, and heat gains and losses are defined in the box to the bottom left of figure 8.1. This information is fed into the main body of the spreadsheet, as indicated by the blue precedent47 arrows, where nodes read left to right, and time reads top to bottom. The calculations used for these were developed by Gilbert48 and are described below. The temperature of node n, at the next time step, p+1, is governed by temperatures of the node, and the nodes either side, n-1, n+1, at the current time step, p, the resistance between the nodes, the size of the time step, and the physical properties of the material. The Fourier equation governing heat flow by conduction, is converted into a finite difference equation that can be solved for each node and each time step, (for derivation refer to Gilbert).

!

Tnp+1 =

"t

Cn

Tn#1p #Tn

p( )Rn,n#1

+Tn

p #Tn+1

p( )Rn,n+1

+ q

$

%

& &

'

(

) )

+ Tnp [1]

(T1-T2) is temperature (°C or K) ΔT is the size of time step (s) C

is the thermal capacity of a node (j/kg) and is a product of Volume (x in 1-Dimensional heat flow), Density ρ and Specific Heat Capacity cp

R is the thermal resistance between nodes (°C/W)

Where

p is the time step, (p+1 is the next time step) n Is the node number (n-1 is the node before, n+1 is the node after) q Is the heat generated within the node For heat transfer by conduction, resistance between nodes is calculated by the equation

!

Rcd

="x

k [2]

47 Precedent arrows in excel show which cells are used to calculate the value in the current cell. 48 Gilbert (2005 & No Date)


Where k is conductivity (W/mK) Δx is the distance (m) The values entered are averages taken for each layer of material considering the effects of conduction in voids, as described in chapter 5.

8.3 Method and Adaptations The HFS is used to model the T11 semi –buffered office as described in chapter 7 and figure 7.2. Each external boundary is assumed to be a perfect insulator except for one wall, and as such heat transfer through this wall is considered in isolation. For the base room temperature as determined by external weather conditions, a sinusoidal temperature profile is assumed. This is modelled on results from the IES model with the casual gains removed. The difference in this base temperature from the previous time step before is added into the temperature difference of the inside room temperature. This is a simplified method of considering the weather effects of room conditions, the limitations of which are described at the end of this chapter. Figure 8.3 shows the simplified weather data (first set of precedent arrows) feeding into the column adjacent to the inside room temperature column, describing the weather generated base temperature of the room. Figure 8.3 also shows the variables feeding directly into the value for inside room temperature (second set of precedent arrows), which are derived from more sources than internal nodes (third set of precedent arrows). This is due to the value for heat generated within the node, q, (refer to equation [1] of this chapter), which is zero in most cases.

Figure 8.3 HFS: Spreadsheet set up – calculation precedents The value for q is calculated as the difference between heat generated and heat lost in the node. In this instance these are equivalent to casual gains and infiltration losses derived from air


changes. The equation for infiltration power losses is described in chapter 6, and is effected by air change rate, volume, specific heat capacity and density of air, and the temperature difference between inside and outside. In the initial models, before the weather data was introduced, the value for q was entered as infiltration alone until the time step at which the casual gains were included in the equation. The infiltration did not effect the temperature until there was a significant difference between internal and external temperatures.

In an early test cell sized model, the time step had to be reduced to one second (compared to 3 seconds for the model of the office, and 60 seconds for the original HFS). This increased the size of the spreadsheet (also decreasing the speed and convenience of the excel file) and meant that a greater number of equations had to be solved. It is suspected that this increased the level of error in the results, and for a very small model with minimal heat gains represented, the resultant temperature was extremely low, compared to the physical test cell. The calculation for the inside room temperature column was broken down into component equations to identify which part of the equation was having the greatest effect. It appeared that the conduction equation, (which considers the effects of the temperatures of the nodes either side) was disproportionately large compared to the effects of the power input, even without infiltration considered. The suspicion was that the scale of the model was the main contributor to this error, but it was considered beyond the scope of this thesis to completely resolve the issue. With increased power input however, the HFS gave results between blocks that were comparable with the test cell. It therefore deemed suitable to test the effects of more elaborate configurations of clay and void for a general performance comparison, as described in chapter 10.

At a larger scale, representing an office, the HFS model gave more realistic results that tallied well with the IES model in terms of peak temperatures. It did however describe the temperatures of the first few nodes rising very quickly to a plateau, representing a much steeper curve than illustrated in IES. Figure 8.4 shows the effect of introducing casual gains for a set time period (the red area). The yellow cells indicate heat being retained by the wall after the casual gains are removed. The small area of red cells represents higher temperatures. The fact that these do not travel far into the wall, suggests that the wall is behaving as a thermally lightweight structure, which was also shown for concrete block walls modelled with a large number of layers. To reduce the error due to the number of layers, further spreadsheets were set up with reduced and simplified layers. This produced slightly improved representations of temperature gradients, as described in chapter 11.

Figure 8.4 HFS: Spreadsheet set up –the effect of introducing casual gains


8.4 Limitations of the HFS Models The adaptations made to the original HFS have proven problematic. It is considered that the most likely explanation is due to the increased number of layers and time steps that have been modelled. It would be extremely beneficial to this study if these issues could have been completely resolved, as the HFS is unique in enabling an understanding of heat transfer within the wall. It is beyond the scope of this thesis and to dissect this problem any further, but it is considered as a vital area for further research into modelling complex materials. Considering the above, it should be noted that the HFS models have been successful in describing the comparative thermal performances between different materials under the same conditions. They have also been very useful in describing the effects of adjusting the position of thermally heavy materials within a wall. This is an area that has been under researched, as far as the author has established.


9 RESULTS: Steady State Analysis

9.1 Test Cell Results Steady state analysis was carried out on the block for configurations 0C, 1C, 2C, 4C and 8C (number indicates number of rows of ECB filled with clay). The heat input was 4.5W, which was removed after 33.9 hours, with data logging continuing for approximately 10 hours. For the graphs introduced in this chapter the following acronyms are used:

CC Cold chamber 0C – 9C Number of Rows of Clay in ECB MID Centre of ECB

TC Test cell AC/h Air Changes Per Hour HC Hot chamber DYN Dynamic

The bottom line in the title of each graph (4.5W – 33.89 HRS – 11.6 AC/h for example) refers to the power input over the period of time indicated and the number of air changes occurring. The larger title (for instance [44 HOURS] in figure 9.1) refers to the time period or key aspect represented by the graph.

9.1.1 Clay Conductivity Derivation The original ECB results were analysed to derive a value for air changes per hour for the test cell as described in chapter 6. This infiltration rate was then applied to the other configurations to confirm conductivity values for the clay powder. It was found that this gave unrealistically high values for conductivity, and the U-Value for each configuration was correspondingly found to increase disproportionately. This is shown in figure 9.1 as a lower hot chamber air temperature above that of the cold chamber, for the increased layers.

Figure 9.1 TC:Hot Chamber and ECB middle air temperature above CC temperature


One reason for this could be that the block was taking a longer time to reach a steady state, and that the temperature difference would have eventually risen had the heat input been continued for longer. It is however unlikely that the temperature differences would have increased enough to give a realistic U-Value, given the trend of the graph up to the point where the power was removed, and that the temperatures had not varied more than 0.05 degrees in the last 1000 seconds. This result is particularly surprising, as for the increased number of rows, the initial temperature differences between the hot and cold sides were higher. This, if anything would have lead to a higher than probable temperature difference at the peak of the graph. This suggests that the initial temperature does not have a notable effect on the readings after 13.9 hours of heat input. The inaccuracy is most probably due to the scale of the test cell, although less of a difference would have been expected between configurations as a result. Due to this inaccuracy, published figures for the conductivity of clay were used from this point, to inform the computer generated models.

9.1.2 Other Observations At the point where the gradient decreases (between 4 and 12 hours from the start) the temperature differences are most notable between 0C and 1C. The difference between 1C and 2C is much less at this point, and on closer inspection of the 2C series there seems to be some abnormality in the curve of the graph, possibly due to a minor change in power input at this point (the watt meter generally registered varying levels of power consumption around an average of 4.5W). This settles down as a steady state is reached, and the differences between the series follow a more logical pattern. There are depreciating temperature differences observed at the peak of the graph with increased rows of clay. There is 1 degree difference between series 0C and 2C, slightly less than 1 degree between 2C and 4C, and just over 1 degree between 4C and 8C (following the initial pattern a 2 degree difference would be expected). This indicates that the effect of thermal mass on reducing peak temperatures lessens as the number of rows increases. It also suggests that the block was not at steady state for all configurations, as this would have given more predictable, incremental temperature differences. Surface temperatures are more evenly distributed at the peak, but a decreasing difference is still observed for increased rows of clay (see appendix 1).

After the power was removed it was observed that the temperature at the mid point of continued to rise. This was most notable with increased layers of clay, (see figure 9.1, and the differences in temperature profiles between figures 9.2 and 9.3). This would indicate that heat transfer was still occurring from the hot chamber surface to the middle of the block, but not registering as a temperature rise in the cold

chamber. It is possible that infiltration in the cold chamber was causing this anomaly, but if anything, this would have registered as a larger temperature difference between chambers.

TC (0C) STEADY STATE WITH 4.5W POWER INPUT

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44

Time (hours)

Tem

p (

deg C

)

4 - HChamber - air (adj)

5 - HChamber - ECB surface

6 - ECB middle

8 - CChamber - air (adjacent)

7 - CChamber - ECB surface

1 - External - air

Figure 9.2 TC: Temperature differences through ECB for configuration OC


Another explanation, would be large amounts of heat stored by the external test cell walls. This would mean that the hot and cold chambers would not heat up as quickly as the air in the centre of the block.

This seems unlikely as EPS has a low thermal capacity. The high emissivity of the paper may have affected this performance, as the initial radiative heat transfer mechanism would be greater than without. There is however, not an obvious reason as to why this would be different for various configurations of clay within the ECB.

9.2 IES Results For the IES tests, configurations 0C to 9C were modelled as two layers, and configurations 0C to 4C were also modelled as 10 layers, as described in chapter 8. Hot chamber temperature above buffer zone temperature is shown in figure 9.4. Both sets result in steeper temperature gradients than the test cell, reaching a plateau much earlier. This was especially true of the 10 layered models, (described as 0C LAYERS to 4C LAYERS in the legend).

The peak temperatures were approximately 10° below those reached in the test cell, for the same power input and infiltration rate. Eliminating infiltration and reducing casual gains to give the same total power input addressed the possible effects of buffer zone conditioning, but this did not affect the results. It was again conceded that the scale was the issue, combined with the very low heat input, which may have caused calculation problems in IES.

At the point at which the power is removed the temperatures drop extremely quickly at first, before settling into a less steep gradient according to the degree of thermal mass in the block. Closer inspection of the peak temperature condition for the two layered set shows a more even spread of temperature differences than the test cell. This is a more realistic resemblance of what should be occurring at steady state for these configurations, (figure 9.5).

TC (8C) STEADY STATE WITH 4.5W POWER INPUT

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Time (hours)

Tem

p (

deg C

)

4 - HChamber - air (adj)

5 - HChamber - ECB surface

6 - ECB 15th row

8 - CChamber - air (adjacent)

7 - CChamber - ECB surface

1 - External - air

Figure 9.3 TC: Temperature differences through ECB for configuration 9C

Figure 9.4 IES: Steady state profiles for 2 layered and 10 layered models


IES: HC AIR - AIR IN BUFFER ZONE4.5W - 33.89 HRS - 11.7 AC/h

2

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Time (hours)

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p (

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C)

OC

1C

2C

3C

4C

5C

6C

7C

8C

9C

[POWER OFF - 33.89 HRS]

Figure 9.5 IES: Temperature differences at ‘power off’’

After the peak, during the cooling period, 0C cools far quicker than the other configurations. This difference decreases with increased layers of clay. This difference could be due to the fact that this configuration is modelled with only one layer, whereas the others are modelled with two. Again this may be a calculation error within IES, or it may indicate that after one row of clay there is less benefit from the thermal mass under these specific conditions. It is difficult to gauge any firm conclusion from these results due to the level of discrepancy from the test cell.


10 RESULTS: Dynamic Analysis

10.1 Test Cell Results The dynamic analysis was performed for configurations 0C to 9C. The heat input was 25W for 0.5 hours and the data logging was continued for a further 7.5 hours. The general pattern is a steep increase in temperature until the power input is removed, at which point the temperature drops very sharply at first before tapering off to a plateau at different rates according to the amount of clay added. It takes much longer for the storage effects of the increased layers of clay to register after the peak. In the steady state tests the increased rows of clay began to register higher temperatures sooner after the peak, before the point at which the gradient tapers off.

TC: HC AIR - CC AIR

25W / 8 HRS / 11.7 AC

-2

0

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7.0

7.5

8.0

Time (hours)

Tem

p (

deg

C)

0C

1C

2C

3C

4C

5C

7C

8C

9C

[8 HOURS]

Figure 10.1 TC: Dynamic temperature profiles for configurations 0C to 9C

The peak of the graph shows a less predictable order of configurations compared to the steady state results. The peak temperature differences are greater for the first few configurations, and then lessen between 3C and 6C, after which point the temperatures generally rise again until 9C, but the pattern is more chaotic, (figure 10.2). One reason for this could be experimental error. If the block had retained heat from one configuration to the next, temperatures may have shown an increase. If this had occurred for 5C to 8C it would explain the discrepancy. Another explanation, is that in order to start each experiment with near to equal surface and air temperatures between chambers, the cold surface of the block was artificially heated and then allowed to cool down until each surface had remained equal for a period of half an hour. This


added heat may have caused reduced temperature differences for the last few configurations, which would indicate that ideally, the results would have continued to converge. This experiment is quite volatile for such a short period of heat input, compared to the longer and lower heat input used in the steady state tests. It would have been ideal to have left at least 3 days between experiments until the temperatures throughout the block had completely evened out, but time constraints did not allow for this.

TC: HC AIR - CC AIR25W / 8 HRS / 11.7 AC

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Time (hours)

Tem

p (

deg

C)

0C

1C

2C

3C

4C

5C

6C

7C

8C

9C

[PEAK]

Figure 10.2 TC: Dynamic temperature profiles at peak temperatures

10.2 IES Results The IES tests showed a smoother peak at 0.5 hours than the test cell. This could be explained by the fact that results were analysed every 6 minutes by IES and every second by the data logger for the test cell. The connections between points on the graph would therefore give an inaccurate picture of temperature change during this short time. The 10 layered models also predicted much higher temperatures than the test cell (approximately 10° higher). The two layered models correlated more closely for the configurations 1C to 9C, which were however more closely grouped together, with 0C giving higher temperature predictions, (see figure 10.3).


Figure 10.3 IES: Dynamic temperature profiles for 2 layered and 10 layered models

The peak graph shows temperatures in the approximate ranges of 25.7°C to 26.8°C for 1C to 9C in IES compared with 25°C to 27.7°C in the test cell, (see figures 10.4 and 10.2). Within the peak temperatures there are some minor differences between the configurations. Figure 10.5 shows these temperature variations at 0.2 hours, 0.3 hours and 0.4 hours. This indicates a reduction in temperatures until a peak, after which temperatures rise gradually to another peak and fall again.

Figure 10.4 IES: Dynamic temperature profiles at peak temperatures


These peaks occur after different numbers of rows at each time step, indicating a small temperature lag. It is shown in figure 10.4 that the heavier weight models allow the temperature to rise fractionally more than the light weight models at first but reach a maximum point, as the temperature continues to rise in the lighter weight model experiments.

IES: HC AIR TEMP at 0.1, 0.2 & 0.3 HRS4.5W - 0.5 HRS - 11.6 AC/h

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1C 2C 3C 4C 5C 6C 7C 8C 9C

ROWS OF CLAY IN BLOCK

TEM

P (

deg

C) 0.2Hrs

0.3Hrs

0.4Hrs

Figure 10.5 IES: Dynamic profiles - Anomalies in temperature around peak


10.3 HFS Results There was difficultly in obtaining realistic results from the HFS for the very small test cell representation. This is believed to be due to the very low heat energy transfer through very small layer thicknesses and the accumulative error that this brought about. There may also have been an error in the equation inputs that could not be found in the time available. At this stage the HFS was instead used to test further configurations of an ECB in a 1m3 test cell with 120W input and 3 AC/h. The aim was not for absolute results but to compare the behaviour of more unusual configurations with one another, as this could not be tested thoroughly in the test cell due to time limitations.

Figure 10.6 HFS: Dynamic temperature profiles in a 1m3 test cell

Figure 10.6 plots temperatures for configurations between 0C and 16C. General profiles were similar to the test cell, but with a more predictable pattern between blocks. There is a reduction in peak temperature between 0C and 1C of approximately 2˚, after which the results converged and there was little noticeable difference between 2C and 16 C. During the cooling down period more differences were observed, and the ECBs with less rows of clay retained the heat for longer. The long term storage for the heavier blocks is not observed for approximately 6 hours, when the order of the configuration results begins to swap round, This was slightly more apparent in the test cell (figure 10.1), and much more apparent in IES, (figure 10.3). This indicates that the period of heat input was not long enough, or intense enough to allow heat to be conducted very far into the block, and that the heat that was absorbed took many hours to return to the room. Configurations 0A5C to 5A5C (indicates number of rows of air before number of rows of clay) were then tested, (see figure 10.7). This indicated that a constant volume of mass located away from the inner face still gave some benefit in terms of reducing peak temperatures, but was more significant after the peak. This pattern was compared to 0C to 5C (figure 10.8).


Figure 10.7 HFS: Dynamic temperature profiles: Increasing void before fixed mass

It was observed that rows 1A5C TO 4A5C are much closer to the 0C end of the scale in terms of thermal behaviour. The spread of results after the peak is again more apparent for both tests. The temperatures for the models with the mass located away from the ECB edge tend to drop much faster than indicated by the 0C model, despite having very similar peak temperatures, and begin to resemble the behaviour of the 1C model.

Figure 10.8 HFS: Dynamic profiles – configurations 0C to 5C

Figure 10.9 shows that increasing the layers of clay at a set point from the material surface has negligible effect on the temperature profile. This would indicate the importance of the first layer of clay.


Figure 10.9 HFS: Dynamic profiles - Increasing mass after fixed void

The general findings were that the current orthodoxy of thermal mass closer to the inside face of a material was proven correct. It was also found that an equal number of rows moved in from the edge incrementally (figure 9.7) gave greater differences in thermal behaviour than an increasing amount of clay a fixed difference from the inside face, (figure 9.9). The practical implications of this would be:

- Thermal mass should be as close to the inside face as possible - If the thermally massive part of the wall is located further in from the edge, adding to

the thickness makes less difference than moving the same amount of thermally massive material closer to the inside face.


11 RESULTS: Scaling Up

11.1 Introduction The experiments were scaled up to represent three different types of office. This was to test the configurations of ECB in a more realistic scenario to see if the same patterns were followed, and to add different types of concrete block wall types into the experiment. It also helped to iron out some of the problems that the IES and HFS models were having with the small scales experiments, and more realistic results were returned. The experiments concentrated on summer performance, as the issue was the ability of the material to limit over-heating. It is assumed that the winter performance would follow the same pattern between materials, but this would be an area for further research. The three office types are listed below.

1. In IES: 16sqm floor area and 2.5m floor to ceiling height. Using T14 block (as in the test cell scale experiment) with 90 W/m2 casual gains from lighting between 08:30 and 17:30 hours, and 5 AC/h ventilation, to represent a high density modular office. This office was buffered from the effects of external weather, and used to test the differences in modelling 2 and 10 layers.

2. In IES and HFS: Using T11 blocks with the same room dimensions, heat gains and

ventilation as above. This was semi buffered, as described in chapter 7, to match how the conditions are represented in the HFS.

The various ECB configurations were tested against heavy weight, medium weight, lightweight and aerated concrete blocks with EPS insulation to the external face. The EPS thickness was varied to give all four wall systems a U-Value equal to that of a T11 block filled with 6 rows of clay.

3. In IES: 240sqm floor area and 3m floor to ceiling height. A stand alone office with no

buffer zone and all external walls represented as the same type of wall build up. A layer of plasterboard was added to the inside face of each material as this would affect thermal performance within the office. The roof and floor were modelled as thermally lightweight. The heat gains were adjusted to 60W/m2 to represent a high density larger office. Ventilation was set to 5 AC/h in the daytime and adjusted to 2 AC/h at night to represent night purging.

The same configurations of ECB and types of concrete block were tested as before, with extra concrete block types considered from market investigations.

11.2 Office 1: 16Sqm / T14 configurations IES was used to test T14 configurations for different numbers of layers. It was found that the two layer models returned temperature predictions that were more spread out than the ten layer models. The air temperature in the increased layer model also rose more steeply. It would appear at this stage that a larger number of layers gives the material the qualities of thermally light weight construction than when modelled with fewer layers. This could be due to accumulative calculation errors in the conduction equations, or it could be that the averaged out


values for layer properties are unrepresentative of the block layers in reality. It would appear that the models with fewer layers give overall temperature profiles that are more in line with what was observed in the test cell, which stands to reason when the quantity of dense clay powder that went in to each row is observed.

Figure 11.1 IES Office 1 – Temperature Profiles over 3 days

11.3 Office 2: 16Sqm / T11 configurations & Concrete blocks This experiment compared various configurations of the T11 block with four types of concrete blocks. It is noted that various densities of block are available and the following list was compiled to indicate where the 4 blocks modelled fit in with real blocks on the market49, (see table 11.1). Block Type (by density) Density

(kg/m2) Conductivity

W/mK SHC

(J/kg˙C) EPS thickness*

(mm) Total thickness**

(mm) IES HEAVYWEIGHT 2300 1.63 1000 81.6 329.1 Hanson: Party Wall 2100 Unspecified 840*** - - Hanson: Evalast Background 1990 1.32 840*** 85 332.5 Hanson: Evalast Facing 1900 1.22 840*** 84.5 332 H

eavy

Hanson: Fenlite Background 1500 0.48 840*** 75 322.5 Hanson: Evalight Background 1450 0.47 840*** 74.7 322.2 Hanson: Evalite Facing 1450 0.47 840*** 74.7 322.2 IES MEDIUMWEIGHT 1400 0.51 1000 76 323.5 Hanson: Fenlite 1350 0.45 840*** 74 321.5 M

ediu

m

Hanson: Superlight Background 1100 0.4 840*** 71.9 319.4 Hanson: Superlite facing 1000 0.36 840*** 69.8 317.3 M

ed - Li

gh t

Hanson: Ultralight Background 850 0.295 65.2 312.7 IES AERATED 750 0.24 1000 59.4 306.9 IES LIGHTWEIGHT 600 0.19 1000 51.1 298.6 Li

ght

Table 11.1 Concrete block properties *thickness to achieve 0.339 W/m2K U-Value

**thickness to achieve 0.339 W/m2K U-Value (includes 12.5mm plasterboard and 20mm render)

***From CIBSE Guide A

49 Hanson (No Date)


The recorded specific heat capacity (shc) of concrete blocks varies between sources. IES for example lists shc as 1000 J/kgK for all weights of concrete block, whereas CIBSE guide A lists shc of aerated concrete blocks as 1000 J/kgK, and 840 J/kgK for light, medium and heavy weight concrete blocks. A value of 1000J/kgK was used for the purposes of this experiment, so the results would if anything give optimistic predictions for concrete block performance. The EPS thickness was varied to give all four wall systems a U-Value equal to that of a T11 block filled with 6 rows of clay, which was identified as the maximum addition of thermal mass in order to retain a sensible U-Value when plasterboard and render were added. Although in reality the availability of different EPS thicknesses are more limited, giving equivalent thermal transmittance values for each material was useful for comparing dynamic thermal behaviour of equally rated systems. The U-Value was 0.353 W/m2K for each without internal or external lining added, and approximately 0.339 W/m2K with 12.5mm plasterboard lining to the inside and 20mm external render. This would satisfy current UK building regulations.

11.3.1 Office 2: IES Results The results showed that 5C and 6C gave a similar performance to the medium weight concrete block modelled, fairly consistently over the course of a week in mid July, for both minimum and maximum temperatures.

IES: T11 OFFICE - SEMI BUFFERED - ROOM AIR TEMP

90W/M2 / 08:30-17:30 / 5 AC

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[1 WEEK]

Figure 11.2 IES Office 2 – T11 Temperature profiles over 1 week

Tuesday and Wednesday were then analysed more closely. It was observed that on each day the gradients of the ECB model temperatures rose more slowly, but continued to rise after the temperatures observed for the concrete block model started to plateau. One explanation for this could be the relatively high conductivity compared to specific heat capacity of the ECBs. This would mean that heat transfer was occurring into the block from the surface, but the heat capacity was not sufficient to retain this heat.


Figure 11.3 IES Office 2 – T11 - Tuesday and Wednesday

Figure 11.3 shows the relationship between the various configurations and external temperature. A slight lag is observed but generally the internal temperatures follow external temperature patterns, even in the absence of solar gain through windows.

11.3.2 Office 2: HFS Results

The HFS returned results in the region of those predicted by the IES models, but much more closely grouped together. The peak temperature ranges were approximately 29˚C to 32.5˚C for the IES model and between 32˚C to 33˚C for the HFS model. The trough temperature ranges were approximately 13˚C to 15.5˚C for the IES model and between 13.5˚C to 14.5˚C for the HFS model.

The simplistic profile is most likely a result of the simplified weather data entered into the model. For the weather temperature, a sinusoidal wave around an average of 16 was set up, based on the temperature profile of unoccupied rooms modelled by IES under the same weather conditions. This would not have allowed for intricacies in base room temperature, which tended to give more of a lag to the temperatures modelled in IES.

HFS: SEMI BUFFERED - ROOM AIR TEMPERATURE90W/M2 / 08:30-17:30 / 5 ACH

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0 4 8

12

16

20

Wednesday -

0

4 8

12

16

20

48

Time (day / hours)

Tem

p (

deg

C)

0C

1C

2C

3C

4C

5C

6C

7C

CONC med

CONC heavy

[2 DAYS]

Figure 11.4 HFS: Office 2 – T11 – Tuesday and Wednesday


HFS: SEMI BUFFERED - ROOM AIR TEMPERATURE

90W/M2 / 08:30-17:30 / 5 ACH

31.5

31.6

31.7

31.8

31.9

32.0

32.1

32.2

32.3

32.4

32.5

32.6

32.7

32.8

32.9

33.0

Tuesday -

0 4 8

12

16

20

Wednesday -

0 4 8

12

16

20

48

Time (day / hours)

Tem

p (

deg

C)

0C

1C

2C

3C

4C

5C

6C

7C

CONC med

CONC heavy

[PEAKS]

Figure 11.5 HFS: Office 2 – T11 – Tuesday and Wednesday peak temperatures

Within the peaks of the graph the relationships of the temperature results between materials correlated well with the IES model. It was found that the 5C and 6C gave similar results to the medium weight concrete model, and that the peak results for 4C and 3C were also falling to the same level on the first day. The step in temperatures from one day to the next would suggest that for the heat gains, ventilation and scale of the room, the walls modelled are retaining too much heat over night. This indicates that the diurnal heat capacity is out of phase with the time period, as discussed in chapter four, leading to incremental rises in peak temperature from day to day. This could have more effect in the HFS than the IES model as the IES model walls will not be perfect insulators, and a certain amount of heat loss, however small will occur through the thick EPS walls. Another possible explanation is that the number of layers, and consequent number of conduction equations that occur between the inside and out side of the block cause an error in the speed at which the heat is returned to the room.

Figure 11.6 HFS: Office 2 – T11 Simplified Layers – Tuesday and Wednesday peak temperatures


The block was remodelled for each configuration using average values for groups of layers as in the IES model, and reducing the number of layers from 51 to 12, as discussed in chapter 7. Comparing figures 11.5 and 11.6 shows that the spread of results between configurations greatly increased when layers were decreased and simplified. The gradient also reduced for the reduced number of layers, and the overall profile resembled the IES T14 office more closely, (which was sheltered from the effects of weather). A similar order in peak temperatures was observed for both sets of models, including the positions of the two types of concrete block. This suggests that although the increased number of layers is creating problems in the overall spread of temperate predictions, it is still useful in describing the general relationship between the ECB configurations and concrete blocks. Figure 11.7 below shows temperatures throughout the block for the existing ECB (0C) and the ECB filled with 7 rows of clay (7C) for the 51 layered models and the 12 layered simplified models. The colours indicate temperatures through the block at various distances from inside face (reading left to right) over time (reading top to bottom). The red areas indicate that the temperature of the node has raised 5˚ above initial temperature, orange indicates 2˚ and yellow indicates 0.1˚. For both configurations the area of red is surprisingly small. This indicates that the temperature of the nodes in these locations do not rise more than 5˚ above initial temperatures for a very long period of time. We know however from the previous graphs, that within this red zone the temperatures are rising very quickly to around 15˚ above initial temperatures. This behaviour is suited to light weight materials more than materials with a high thermal mass. The fact that the concrete blocks are recorded as following the same pattern indicates that it is not the ECBs that are performing as a light weight material, but that the equations entered into the HFS (or accumulative errors due to the sheer number of equations) that are misrepresenting the materials in this instance.

Figure 11.7 HFS: Office 2 – T11 Thermal behaviour of 0C and 7C for detailed and simplified models


Another observation is that high and mid range temperatures are registered for a shorter time in the 7C than the 0C 51 layered model, but low range temperatures remain in the block for longer. In the 12 layered simplified models the orange mid range temperatures continue from one day to the next (shown as a link between red areas). This is more representative of diurnal heat storage, but the small area of red (higher temperature storage) is still surprising. Figures 11.8 and 11.9 below, show the effect of thermal mass on temperature gradients through the simplified ECB configurations 0C and 9C at hourly intervals.

Figure 11.8 HFS: Office 2 – T11 Simplified Layers – Hourly temperature gradients through 0C

Figure 11.9 HFS: Office 2 – T11 Simplified Layers – Hourly temperature gradients through 9C


For both figures 11.8 and 11.9 the distance from the inside face of the wall is represented by the x-axis and node temperatures are represented by the y-axis. The small increase in temperature during the first 8 hours (blue series and blue dotted series) indicates that there is negligible heat flow into the block at this time (the heat gains would only be a result of the weather profile during this period). During the working day (from the red series to the red dotted series) temperatures rise suddenly, and remain above 30°C for this period. Between 17:00 hours and 18:00 hours, when the heat input is removed, temperatures drop suddenly, but are retained within the block to different extents in each model. Throughout the evening (from the purple series to the purple dotted series), the room temperatures are similar for both models, but the temperature gradients within the wall follow different patterns. Figure 11.8 shows that for the 0C configuration, higher temperatures are absorbed more quickly into the block. This can be seen by the form of the working hours series, which gradually swells towards a higher temperature towards the end of the working day. Figure 11.9 shows that for the 9C configuration the temperature gradients remain much more steeper during this period, but during the evening the gradients drop considerably, and at 24:00 hours the temperatures at approximately 130mm into the block are at least 1.5° higher than in the 0C configuration.

11.4 Office 3: 240Sqm / T11 configurations & Concrete blocks For the third office model, more types of concrete block were modelled with varying amounts of EPS insulation to give equal U-Values. The purpose was to investigate comparative summer time thermal performances for each configuration of ECB. For this experiment, a stand alone 240sqm office was modelled with a floor to ceiling height of 3 meters. All external walls were modelled as the same material in each case, with 12.5mm plasterboard lining to the inside and 20mm external render. This gave U-Values of approximately 0.339 W/m2K for each as described in section 11.3.

Figure 11.10 IES: Office 3 – General temperature profiles of multiple blocks in July


Figure 11.10 gives a general picture of temperature profiles over the month of July (based on London Kew Garden weather files), for all blocks modelled compared to external temperature. The temperature ranges between approximately 17°C and 27°C.

IES: 240 SQM OFFICE - Example Max Room Temperatures

26

26.1

26.2

26.3

26.4

26.5

26.6

26.7

26.8

26.9

27

16

17

18

Time (Hours)

Tem

pera

ture

(D

eg C

)

IES - Light

IES - Aerated

0C

Hanson Light ULB

2C

Hanson Medi-Light SLF

Hanson Medi-Light SLB

3C

1C

Hanson Medium FL

Hanson Medium - ELF

Hanson Medium - ELB

4C

Hanson Medium - FLB

IES - Medium

5C

6C

7C

8C

9C

Hanson Heavy - ELF

Hanson Heavy - ELB

IES - Heavy

Figure 11.11 IES: Office 3 – Typical peak temperature profiles of multiple blocks

Analysing a typical temperature peak (figure11.11) shows that the three heavy weight concrete blocks reduce peak temperatures the most, followed by 9C to 5C; the upper end of the medium weight blocks and then 4C. The biggest surprise is the position of the configuration 1C as will be discussed in more detail later. The fact that configurations 3C and 4C fall at either end of the hanson medium weight range is also surprising, and an improvement on predictions for the smaller scale office. It is also worth noting that configuration 5C is shown to reduce temperatures below the level of all of the blocks classed as medium weight. The temperature range is, however, less than 1 degree at this point. This is probably due to the simplicity of the model, which does not include glazing, and therefore the extremes of solar gain are not considered. The intention was to limit the effects of factors that were harder to identify. The addition of windows, as well as more comprehensive ventilation and casual gain strategies would be an area for further study. Figures 11.12 and 11.13 show hours of over heating for comfort thresholds of 25˙C and 26˙C respectively. These show both 0C and 1C performing better than expected in terms of reducing hours of over-heating. No obvious error was found in the data entered to explain this. The anomaly for the 0C and 1C configurations is most apparent for the 25°C threshold where 0C and 1C predict hours of overheating equivalent to the low end and high end of the medium weight concrete block range respectively. Configuration 1C is shown to allow fewer hours of over heating than 5C in this scenario, (figure 11.9). For the 26°C threshold, these two configurations move back towards their predicted places in the order of wall type performance, but still predict fewer hours of over heating than would be expected, (figure 11.10). There are also changes in the order of block performance at the upper end of the scale, with 9C reducing the comparative hours of over heating for a 26°C threshold, to


rank 2nd after the IES heavy weight block, and 4C and 5C performing equivalently to the top end of medium weight blocks.

Hours Over 25 degC in July

0

5

10

15

20

25

30

35

40

IES H

eavy

Hanson H

eavy -

ELB

Hanson H

eavy -

ELF

9C

8C

7C

6C

IES M

ediu

m 1C

5C

Hanson M

ediu

m -

FLB

Hanson M

ediu

m -

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Hanson M

ediu

m -

ELB

Hanson M

ediu

m F

L

4C

0C

Hanson M

edi-

Lig

ht

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3C

Hanson M

edi-

Lig

ht

SLF

Hanson L

ight

ULB

2C

IES A

era

ted

IES L

ight

Wall Type

Nu

mb

er o

f H

ou

rs

Figure 11.12 IES: Office 3 – Hours of Over Heating for 25°C Threshold

Hours Over 26 degC in July

0

1

2

3

4

5

6

7

IES H

eavy

9C

Hanson H

eavy -

ELF

Hanson H

eavy -

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7C

6C

5C

IES M

ediu

m 4C

Hanson M

ediu

m -

ELF

Hanson M

ediu

m -

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Hanson M

ediu

m -

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1C

Hanson M

ediu

m F

L

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edi-

Lig

ht

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3C

Hanson M

edi-

Lig

ht

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0C

2C

Hanson L

ight

ULB

IES A

era

ted

IES L

ight

Wall Type

Nu

mb

er o

f H

ou

rs

Figure 11.13 IES: Office 3 – Hours of Over Heating for 26°C Threshold

Regarding the OC and 1C results, it may be the case that the higher the threshold the more predictable the hours of over-heating modelled in each case. The suspicion is, that following the pattern of the T11 office (see figure 11.3), the gradient for fewer rows of clay are less steep but continue to rise after the heavier weight models reach a plateau. This suggests that for less extreme temperatures, it is more effective to have a thermally lighter material. The next step would be to investigate this further and to find out which levels of heat gains are most suited to which configurations of block. This would also have a bearing on thermal behaviour during winter months, and it would be useful to investigate the effects of different heating patterns on different block configurations.


12 Implications and Recommendations for Further Research

12.1 Introduction Given the results obtained from this study, this chapter explores the implications in terms of environmental savings of using ECB configurations, compared to the concrete block with which thermal performance compare most closely. It goes on to explore other implications arising from the research in terms of practical applications, considering production, buildability and cost. Recommendations are made for further research as they arise.

12.2 Environmental Savings Approximations of the environmental impact of concrete blocks and ECBs have been made using information obtained from the BRE Approved Environmental Profiles for wall systems50. The profiles used related to 1 sqm of the following wall types: 1. Internal plaster board, rockwool insulation, solid heavyweight concrete block and render 2. Internal plaster board, rockwool insulation, solid aerated concrete block and render 3. Internal plaster board, solid aerated concrete block and render 4. Expanded Polystyrene Insulation (15kg/m3) based on a thermal resistance of 1.45 W/m2K 5. Internal plaster board, NBT Thermoplan – 365mm masonry units (ECBs) and render The following assumptions were made to derive values for the medium weight wall with EPS insulation and for the ECB T11 6C and 4C block (filled with 6 and 4 rows of clay respectively).

1. The differences between wall types 2 and 3 above were taken as the values for rockwool insulation, which were then removed from the heavyweight concrete profiles to derive values for this system without rockwool (as this is presumed to be internal grade insulation).

2. An average was taken between heavy and aerated block wall systems for the medium weight concrete block wall system.

3. The EPS values were increased proportionally to represent the thickness used for the heavy and medium weight concrete blocks and these were then added to the totals for these wall systems.

4. The ECB values were increased proportionally with the increased density of the block with 4 or 6 rows filled. This does not take into account the proportion of the profiles attributed to the plasterboard lining and the render, so would give a slightly higher value than if these had first been removed. This also does not account for the fact that the clay powder is not fired. This does however give the opportunity for revisiting the method of adding the clay in powder form, for instance by working it into the extrusion process.

Tables 12.1 (a and b) give the assumed environmental profiles for the 3 wall systems derived from the above process. These are obviously approximations given the above limitations, which

50 BRE Certification Ltd (2002-a,b,c,d & 2006)


were left as such due to time constraints. On the whole however, these results would be conservative in terms of predicted environmental savings. Two anomalies are the categories ozone depletion and fossil fuel depletion. The original figures for ECB blocks were equal to and less than these environmental indicators respectively. It is not clear which part of the wall system these refer to. The equivalent values for ozone depletion, for the original ECB and concrete blocks could indicate that this is attributed to the plaster board, as this is common to both wall types. However, if polystyrene is being used as a sacrificial material in the ECB this would account for some level of pollution. This is an area which needs much more thorough research.

Table 12.1a (above) Environmental savings for ECB 6C over medium weight concrete block walls per m2 wall system Table 12.1b (right) Environmental savings for ECB 4C over medium weight concrete block walls per m2wall system Limitations aside, the 4C and 6C walls indicate large environmental savings in most areas. Percentage savings from the medium weight concrete block reference point, indicate that there are 25.4% and 30.6% reductions in CO2 emissions respectively for configurations 4C and 6C. This alone would be a significant saving over a large building. The major savings, however can be seen in the pollution to air, and pollution to water categories, along with water extraction, waste disposal and transport pollution and congestion. For all of these, environmental savings are between 62.1% and 99.6%. The transport pollution figure is quite surprising bearing in mind that ECBs are currently imported from Germany. The comparatively high figure for the concrete block wall system may stem from the import of cement from Asia, as is common practice. Or it could be a culmination of the many raw materials and additives that go in to making concrete. Along with the environmental factors involved in comparing these wall systems, there are other considerations concerned with the practicalities of delivering this product, which are discussed below.

12.3 Production The initial idea for this study was to fire blocks of various configurations from scratch, which would have varying densities throughout. The modification of this approach to using clay powder has allowed an easier experimental process. In terms of the practical applications for this research, it would seem sensible to return to the idea of extruding the configuration into the form from the outset before the block is fired. One limitation of this would be that the extruded clay, due to the sacrificial materials used, has a lower density and conductivity than the compressed clay powder, which would give less thermal mass benefits than this study has shown. It would however, retain a lower U-Value for a thicker layer of solid ECB.

Issue Unit CONC-M Total ECB 6C Saving (Units) Saving %

Climate Change kg CO2 eq 59 44 15 25.4

Acid Deposition kg S02 eq 0.51 0.18 0.332 65.2

Ozone Depletion kg CFC11 eq 7.9E-11 9.99388E-11 -2.09E-11 -26.5

Pollution to Air: Human Toxicity kg tox 0.75 0.20 0.547 73.0

Pollution to Air: Photochemical Ozone Creation Potential kg ethene eq 0.05045 0.015 0.035 69.9

Pollution to Water: Human Toxicity kg tox 3.88633E-06 0.00000001 0.0000039 99.6

Pollution to Water: Ecotoxicity m3 tox 229.2 5.6 224 97.6

Pollution to Water: Eutrification kgP04 eq 0.04 0.016 0.03 62.1

Fossil Fuel Depletion toe 0.0173 0.018 -0.0004 -2.1

Minerals Extraction tonnes 0.33 0.32 0.01 2.7

Water Extraction litres 489.63 81 409 83.5

Waste Disposal tonnes 0.0261 0.0043 0.022 83.5

Transport Pollution & Congestion: Freight tonne.km 81.9 18 64 78.4

ECB 4C Saving (Units) Saving %

41 18 30.6

0.16 0.345 67.7

9.29017E-11 -1.39E-11 -17.6

0.19 0.561 74.9

0.01411 0.036 72.0

1.29357E-08 0.0000039 99.7

5.2 224 97.7

0.02 0.03 64.8

0.0165 0.0009 5.1

0.29 0.03 9.5

75.26 414 84.6

0.0040 0.022 84.7

16.5 65 79.9


This area requires much more research into the extrusion and firing process, in order to understand the possibilities of forming various configurations of block. Ideally the density as well as the configuration could be varied to intensify the thermal storage capacity of the inside face of the wall. This theoretically could be achieved by varying the amount of sacrificial material in the ECB mix through the block, but may be more complicated in practice. The addition of other insulative materials such as warmcel (recycled newspaper), was also considered for use in this experiment, but given that the total conductivity of the air voids was calculated as equivalent to warmcel, this was removed from the scope of this study. By varying configurations of block at the extrusion end of the process, it could be conceivable that larger voids could be formed to the outside, and that these could be filled with insulation, (see figure 12.1). The insulation would be more effective than air for bigger voids, as the effects of convection are greater.

This idea has been explored by Ziegel, in the form of a block with insulation evenly spaced through it, (see appendix 2). If these voids were gradually increased the intensity of the thermal capacitance and thermal resistance would be increased, and the block could be made more efficient over a shorter width, which is one of the main benefits of using a concrete block EPS solution. The creation of a large void to enclose the outer extremes of insulation would offer protection from the elements and negate the need for a rigid, and environmentally harmful product. There is also scope for varying the structural line of the block so that it imitates a two layer material, allowing the first half to be dedicated to thermal mass and structure and the second half to be dedicated to insulation.

12.4 Buildability The major issue with use on site of the amended ECB blocks is the increased weight. This would lead to the necessity of two person lifting, and may lead to smaller block production. If the solid clay part of the block is not fired into the matrix at the production stage, then this would add complications to the building process. It is intended that a line of enquiry noted above, in terms of distinguishing between the heavy and light side of the block be followed, which could ultimately lead to a thinner version of the configurations explored so far. Block cutting could also become more difficult with varying densities and added materials, and prefabricated blocks cut to various angles, or smaller blocks may need to be developed. It may also be necessary to develop blocks with inbuilt services routes to avoid problems of chasing into the material on site. 12.5 Cost The main cost implications of using ECBs over concrete blocks and EPS are the use of an little known material (in the UK), and the loss of floor space due to block size.

Figure 12.1 ECB configuration ideas for future research


The loss of floor space is a serious consideration in tight sites. Table 12.1 gives potential total block thicknesses for various block densities (due to their conductivity). The ECBs investigated with the same internal and external linings would have a total thickness of 397.5mm. Compared to the thicknesses indicated of concrete block and EPS build ups this is would signify between approximately 70mm and 100mm increase in total wall depth, which would lead to a significant loss in letable floor area. Further investigation would be needed into thermal mass additions to a 300mm block, but the immediate problem with the reduced thickness, is the reduced insulation level. Different approaches to the configuration as described by figure 12.1 could possibly reduce this thickness, if less material was needed due to less thermal bridging. Other cost considerations are involved in the

production and construction processes. If the clay is added in at the firing stage, then the costs would be proportional to the extra clay used, potentially with an increased fuel demand for firing. This should also be factored into environmental costs. If separate materials are added at different stages, this could drive costs up, due to material costs themselves, but also to added labour. There is also a cost implication of the complexity of the system on site, so it would be ideal if materials were fully integrated before this point. 12.6 Summary From this research it has been shown that there are definite environmental savings to be made by using a modified ECB. This would need to be looked at in more detail in order to iron out areas of uncertainty such as CFC use, and fossil fuel depletion. The investigations into this have only scratched the surface of potential issues, and this would require far more research. There is also scope for more research into how the results of this investigation can be developed further into practical solutions. It would be necessary to learn more about the extrusion and firing processes in order to develop more specific ideas for configurations and materials to be used. It would also be beneficial to investigate ideas of varying the structural matrix to work more efficiently with the thermally heavy and lightweight aspects of the block.

Block Type (by density) Total thickness*

(mm) IES HEAVYWEIGHT 329.1 Hanson: Party Wall - Hanson: Evalast Background 332.5 Hanson: Evalast Facing 332 H

eavy

Hanson: Fenlite Background 322.5 Hanson: Evalight Background 322.2 Hanson: Evalite Facing 322.2 IES MEDIUMWEIGHT 323.5 Hanson: Fenlite 321.5 M

ediu

m

Hanson: Superlight Background 319.4 Hanson: Superlite facing 317.3 M

ed - Li

gh t

Hanson: Ultralight Background 312.7 IES AERATED 306.9 IES LIGHTWEIGHT 298.6 Li

ght

Table 12.2 Comparative thicknesses of concrete block EPS wall systems *thickness to achieve 0.339 W/m2K U-Value (includes 12.5mm plasterboard and 20mm render)


13 Conclusions This thesis has tested the dynamic thermal performance of adding rows of clay to an ECB. This has been carried out through physical test cell experiments along side two types of computer simulations (IES and HFS) informed by analysis of existing ECB thermal properties. The test cell gave an insight into the complexity of the material, and computer simulation was then used to investigate its performance at a larger scale and in more detail. IES was used to test the ECB configurations for two sizes of office, against various concrete blocks. HFS was used to validate the relationships shown, and to give an insight into thermal behaviour within the block. HFS was also used to test the implications of varying the order of clay and void within ECBs. These experiments led to the identification of similarly performing ECBs and concrete blocks, and the comparisons of their relative environmental indicators. Practical implications of the results were then considered and ideas for further research introduced. The following sections present the conclusions drawn from the experiments undertaken, in terms of comparisons of ECB blocks and concrete blocks, the limitations of ECBs, and the location of thermal mass. Scope and Limitations of the study will then be discussed.

13.1 ECB Comparisons to Concrete Blocks

ECBs with 4 to 6 rows filled with clay were found to create thermal environments that closely resembled medium weight concrete blocks, in UK high-density office scenarios.

Maximum and minimum temperatures that were reached in the whole range of ECB models were found to be spread quite evenly throughout the concrete block types, as were comparisons of numbers of hours over-heating for a 25°C and 26°C threshold. Most of the heavier ECBs fell between medium and heavy weight concrete blocks. The ECBs with little or no added clay compared well with light and medium light concrete blocks. The models were very simple representations of offices that considered casual internal gains in isolation from direct solar gain, in order to reduce the variables. There were slight differences in the profiles between maximum and minimum temperatures observed, which are described in chapter 11. These slight variations and the effects of more complex heat gain and ventilation patterns would be an area for further study.

There are significant environmental savings to be made by using ECBs with 4 to 6 rows of added clay, including: - 25.4% and 30.6% reductions in CO2 emissions - Between 62.1% and 99.6% savings for other environmental indicators

including pollution to air and water, water extraction, waste disposal and transport pollution and congestion51

These findings were based on a set of assumptions and adaptations to BRE Approved Environmental Profiles52, which are detailed in chapter 12. It is notable that environmental issues

51 For units and more detail, refer to chapter 12, tables 12.1 (a and b) 52 BRE Certification Ltd (2002 - a,b,c,d & 2006)


other than CO2 emissions were found to be most notable. It is difficult in the present political climate to address these issues, as CO2 is more recognisable to most people as the biggest risk. It is however, very important to keep a check on every pollutant being released into the ecosystem, and resource use attributed to a method of construction. This includes consideration of secondary materials that must be used within a construction system to enable it to perform to industry standards. In this case rigid insulation and increased levels of cement significantly add to the environmental impact of the concrete block alone. The degree of water extraction (490 litres per square meter) and pollution (229 m3tox) per square meter of medium concrete block and EPS wall system are significant, as clean water is such a vital and often scarce resource. This is of particular consequence when production facilities are located in the majority world for economic reasons, and the local environment suffers disproportionately to the environment in which the end product is used. This and other issues of equity have been beyond the scope of this thesis, and should be considered in future research when comparing the impacts of various materials.

13.2 ECB Limitations

The ECB configurations would have a total thickness of approximately 80mm more than the equivalent concrete blocks. There is not an established history of ECB use in the UK.

These are serious considerations in terms of cost. The thickness and consequent loss of letable floor space, and the risk attached to unknown construction systems within the industry, tend to cause more problems in specification than the costs of the materials themselves. On this basis it can be difficult to persuade clients to choose the more environmentally benign options. This problem would be most easily solved by legislation setting limits on pollution and resource extraction for construction materials. It is, however, most likely to fall to manufacturers of more benign materials to continue to enhance their products to make them more commercially viable whilst retaining their low environmental impact. This is a difficult task, and it is often easier to meet a set of standards designed to tackle one issue, by using a product that creates others. There is therefore a recognised need for industry standards and building regulations to incorporate a more comprehensive set of requirements for the materials allowed for use in construction. This would include readdressing limits that have been set around certain established manufacturers.

ECBs are not entirely benign.

There are issues involved in the production process that would need more investigation. Polystyrene use as a sacrificial material would certainly cause environmental problems, whereas sawdust would be less harmful. The fact that the material is fired (although only to half the temperature of cement) means that there are still CO2 emissions attributed to production. The lack of a UK manufacturer adds to embodied energy due to travel, but this could be rectified by demand. ECBs still involve resource extraction, although global clay reserves are considered extensive53. Extraction also involves energy use, which would need to be investigated further. Generally ECBs have less impact than the concrete systems with which similar thermal benefits are observed. It would be interesting to compare this to other types of construction. For example lightweight systems with phase change materials, which absorb heat energy using a very thin layer of material.

53 Berge (2000, Pg 4)


13.3 Location of Thermal Mass The following conclusions are drawn from section 10.4.

The current orthodoxy of locating thermal mass close to the inside face of a material is correct.

Experiments using the HFS have shown that moving the clay away from the block surface does reduce its thermal mass benefits considerably. It would be beneficial to conduct further tests at larger scales.

Fixed volumes of mass at varying distances from the edge give greater results than increased volumes of mass at a fixed distance.

This was tested by adding rows of clay at varying depths in the wall. It was found that if the thermally massive part of the wall is located further in from the edge, adding to the thickness makes less difference than moving the same amount of thermally massive material closer to the inside face.

13.4 Scope and Limitations of the Thesis During the course of this study the scope of the investigation has shifted slightly from determining specific configurations for levels of heat gain, towards analysis of the various methods of modelling the materials used, and testing their behaviour in a more limited range of conditions. Theoretically the results could have been arrived at by computer simulation alone. The use of a test cell did however give a counter point, which caused greater scrutiny of the simulation methods used. Without this counter point the investigation may have been developed further to include different levels of heat gain and suggest specific configurations for specific circumstances. With the knowledge of the materials’ performance in reality however, if only at a small scale, the recommendations for further research would be for a return to larger scale physical modelling. This could be developed to incorporate the ideas discussed in chapter 11 regarding more extreme variations in form. The HFS would be developed and refined alongside this to enable comparisons to be drawn. This research has led to results derived from a set of assumptions. These have evolved and been revised throughout the development of the investigations to increase the accuracy of the conclusions drawn, but should still be considered as areas for potential error. Of general consideration is the potential for human error and equipment inaccuracy, which are applicable to the entire process. One of the specific limitations has been the scale of the initial experiments. This stemmed from the large perimeter to surface ratio in the test cell and computer simulations, and possible calculation problems in IES and HFS from the minimal heat input. The initial tests were therefore limited in their usefulness in terms of temperature predictions, but still useful in identifying patterns of behaviour. The need to simplify material properties in the computer simulations could also have caused a significant degree of error, due to the many layers of information entered and giving rise to potential accumulative errors. The conclusions derived from computer simulations have a consequent degree of uncertainty in terms of predicting precise temperatures. However, the continuing patterns between predicted ECB configurations and concrete block models has been encouraging with regards to determining general relationships between these materials.


Appendices Appendix 1: Test Cell Photos


Appendix 2: Ziegel Data Sheets: ECB Developments54

54 Ziegelwerk Klosterbeuren, (No Date-a & No Date-c),


References Baker, NV & Steemers, K (1994), Energy & Environment in Non-Domestic Buildings – A Technical Design Guide, Cambridge Architectural Research Ld, and University of Cambridge Berge, B. (2000), The Ecology of Building Materials, Architectural Press Bill Dunster Architects et al. (2005), UK Housing and Climate Change Heavyweight vs. lightweight construction, Arup Research & Development Available at: www.architecture.com/fileLibrary [Accessed 15th March 2007] Gibert, B (2005), Thermal Mass and the Effects f Dynamic Heat Flow, MSc Thesis, School of Computing and Technology, University of East London Gibert, B (No Date), Advanced Modelling of Dynamic Heat Flow – A Tutorial (Draft document), Bobby Gilbert & Associates Ltd Givoni, (1987), Passive Solar Journal, Volume 4, No 1, Marcel Decker Inc Holman J.P. (2002), Heat Transfer – 9th Ed, McGraw-Hill Higher Education Hulme, M et al (2002), Climate Change Scenarios for the United Kingdom: The UKCIP 02 Briefing Report, Tyndall Centre for Climate Change Research IPPC (2007), Working Group III contribution to the Intergovernmental Panel on Climate Change Fourth Assessment Report - Summary for Policymakers, IPPC, WMO & UNEP Available at: http://www.ipcc.ch/ [Accessed 24th May 2007] Issacs N. & Donn, M. (1994), Effect of Thermal Mass on House Energy Use and Internal Temperatures, Building Performance Research, Victoria University of Wellington Jones, GF & Wray, WO. (1992) Simplified Methods, chapter in: Balcomb, JD (Ed) (1992) Passive Solar Buildings, Massachusetts Institute of Technology Johnson, TE. (1981) – Solar Architecture – The Direct Gain Approach, Timothy Johnson Knight, I & Dunn, G (No Date), Evaluation of Heat Gains in UK Office Environments, Available at: www.cribe.uk.com/services/buildings/CIBSEHeatgains [Accessed 11th May 2007] Mazria, E. (1979), Passive Solar Energy Book, Edward Mazria McMullan, R (2002) Environmental Science in Building, Palgrave MacMillan Metcalf, G (2007) Speaking on behalf of UKCIP at London Heat Island Conference, RIBA London Roaf S, (2004), Closing the Loop – Benchmarks for Sustainable Buildings, RIBA UK Climate Impacts Program - UKCIP (2002), Climate Change Scenarios for the United Kingdom: The UKCIP 02 Briefing Report, Tyndall Centre for Climate Change Research Webb, R (2007) Speaking on behalf of XC02 at London Heat Island Conference, RIBA London Technical Guides and Data Sheets Bouyer Leroux, (No Date), Murs Bio’bric, Product Guide BRE Certification Ltd (No Date) Environmental profiles: life-cycle assessment of construction products – guidance document, Crown and Building Research Establishment Available at: www.bre.co.uk/filelibrary [Accessed 20th June 2007]


BRE Certification Ltd (2002-a) Approved Environmental Profile: Characterised and Normalised data for: 1 Square meter of Installed External Wall: Solid Masonry Wall Construction: Rendered Solid Dense Blockwork with rock wool insulation and plasterboard dry lining, paint, Crown and Building Research Establishment BRE Certification Ltd (2002-b) Approved Environmental Profile: Characterised and Normalised data for: 1 Square meter of Installed External Wall: Solid Masonry Wall Construction: Rendered Solid Aerated Blockwork with rock wool insulation and plasterboard dry lining, paint, Crown and Building Research Establishment BRE Certification Ltd (2002-c) Approved Environmental Profile: Characterised and Normalised data for: 1 Square meter of Installed External Wall: Solid Masonry Wall Construction: Rendered Solid Aerated Blockwork Plasterboard/plaster, paint, Crown and Building Research Establishment BRE Certification Ltd (2002-d) Approved Environmental Profile: Characterised and Normalised data for: 1 Square meter of Installed Insulations: Expanded Polystyrene Insulation (15kg/m3), Crown and Building Research Establishment BRE Certification Ltd (2006) Approved Environmental Profile: Characterised and Normalised data for: 1 Square meter of Installed External Wall: Solid Masonry Wall Construction: NBT Thermoplan – fired clay masonry units 365mm, lime:cement render and plasterboard and paint, Crown and Building Research Establishment British Standard EN ISO 8990:1996 (1996) Thermal insulation - Determination of steady-state thermal transmission properties - Calibrated and guarded hot box CIBSE – The Chartered Institute of Building Services Engineers (1999) Guide A – Environmental Design, CIBSE London Construction Resources, (No Date), ThermoCellit Blocks – Masonry Honey Combe Insulating Blocks, Product Guide

Gesellechaft für Qualitätssicherung und Materialprüfung mbH, (1998), Poroton – T14 – Planziegeln und Dunnbettmortel, (ECB T14 Data Sheet) Hanson (2007), Aggregate Blocks Technical Manual, HANSON Building Products Natural Building Technologies, (No Date-a), Warmcel 100, Data sheet Natural Building Technologies, (No Date-b), NBT Thermoplan System, Product Guide Office of the Deputy Prime Minister (2006) Approved Document L2A: Conservation of fuel and power (New buildings other than dwellings), NBS for the Office of the Deputy Prime Minister Ziegelwerk Klosterbeuren, (No Date-a), 1.5 ThermoPlanT11 / T11 V.Plus, Data sheet Ziegelwerk Klosterbeuren, (No Date-b), ThermoPlan T14, Data sheet Ziegelwerk Klosterbeuren, (No Date-c), 1.1 ThermoPlan MZ8/MZ8 V.Plus, Data sheet Interviews and Emails

Earland, S. of Heat Transfer Society (2007), Email dialogue with the author

Sommer, A of Ziegel (2006), Telephone interview with Kristin Trommler on behalf of the author

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