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Energy Audits

The book’s companion website at www.wiley.com/go/al-shemmeri provides full support for both students and lecturers:

● solutions to tutorial problems, showing full workings ● discussion topics ● PowerPoint presentations for each chapter ● spreadsheets for students’ calculations ● samples of energy audits ● exam questions + answers

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Al-Shemmeri_ffirs.indd iiAl-Shemmeri_ffirs.indd ii 7/8/2011 10:39:06 AM7/8/2011 10:39:06 AM

Energy AuditsA Workbook for Energy Management in Buildings

Tarik Al-ShemmeriProfessor of Renewable Energy TechnologyStaffordshire University

A John Wiley & Sons, Ltd., Publication

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This edition fi rst published 2011 © 2011 by Blackwell Publishing Ltd

Blackwell Publishing was acquired by John Wiley & Sons in February 2007. Blackwell’s publishing program has been merged with Wiley’s global Scientifi c, Technical and Medical business to form Wiley-Blackwell.

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All reasonable attempts have been made to contact the owners of copyrighted material used in this book. However, if you are the copyright owner of any source used in this book which is not credited, please notify the Publisher and this will be corrected in any subsequent reprints or new editions.

Library of Congress Cataloging-in-Publication Data

Al-Shemmeri, Tarik. Energy audits : a workbook for energy management in buildings / Tarik Al-Shemmeri. p. cm. Includes bibliographical references and index. ISBN-13: 978-0-470-65608-2 (pbk.) ISBN-10: 0-470-65608-5 (pbk.) 1. Buildings–Energy conservation–Handbooks, manuals, etc. 2. Energy auditing–Handbooks, manuals, etc. 3. Energy conservation–Handbooks, manuals, etc. I. Title. TJ163.3.A35 2011 658.26–dc23

2011021991

A catalogue record for this book is available from the British Library.

This book is published in the following electronic formats: ePDF 9781119950295; ePub 9781119950301; Mobi 9781119950318

Set in 9/12.5pt Interstate by SPi Publisher Services, Pondicherry, IndiaPrinted in Singapore

1 2011

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v

Contents

Preface xi

Acknowledgements xiii

Dimensions and Units xv

List of Figures xxi

List of Tables xxv

1 Energy and the Environment 1

1.1 Introduction 2

1.2 Forms of energy 2

1.2.1 Mechanical energy 2

1.2.2 Electrical energy 3

1.2.3 Chemical energy 4

1.2.4 Nuclear energy 4

1.2.5 Thermal energy 5

1.3 Energy conversion 6

1.4 The burning question 8

1.4.1 Combustion of coal 9

1.4.2 Combustion of oil 10

1.4.3 Combustion of natural gas 10

1.5 Environmental impact from fossil fuels 11

1.6 Energy worldwide 12

1.7 Energy and the future 13

1.7.1 The dream scenario 15

1.7.2 The renewable scenario 15

1.8 Worked examples 15

1.9 Tutorial problems 19

1.10 Case Study: Future energy for the world 20

2 Energy Audits for Buildings 23

2.1 The need for an energy audit 24

2.2 The energy benchmarking method 25

2.2.1 Benchmarking step by step 25

2.2.2 How savings can be achieved 29

2.3 The degree-days concept 33

2.3.1 Regression of degree-day and energy

consumption data 33

2.4 Energy Performance Certificates 34

2.5 Worked examples 36

2.6 Tutorial problems 43

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vi Contents

3 Building Fabric’s Heat Loss 45

3.1 Modes of heat transfer 46

3.2 Fourier’s law of thermal conduction 46

3.2.1 Conduction through a planar wall 46

3.2.2 Radial conduction through a pipe wall 47

3.3 Heat transfer by convection 48

3.3.1 Convective heat transfer: experimental correlations 49

3.3.2 Free convection 50

3.3.3 Forced convection 50

3.4 Heat transfer through a composite wall

separating two fluids 51

3.5 Heat exchange through a tube with convection

on both sides 52

3.6 A composite tube with fluid on the inner and outer surfaces 53

3.7 Heat transfer by radiation 54

3.8 Building fabric’s heat load calculations 55

3.9 Energy efficiency and the environment 57

3.9.1 Space heating 57

3.9.2 Insulation standards 58

3.9.3 The economics of heating 58

3.10 Worked examples 60

3.11 Tutorial problems 67

4 Ventilation 69

4.1 Aims of ventilation 70

4.2 Air quality 70

4.2.1 Minimum fresh air requirements 71

4.2.2 Composition of respired air 71

4.3 Ventilation methods 73

4.3.1 Natural ventilation 74

4.3.2 Mechanical or forced ventilation 75

4.4 Ventilation flow calculations 76

4.4.1 Volume flow calculations 76

4.4.2 Ventilation heat load calculations 76

4.4.3 Ventilation calculations based on CO2 build-up 76

4.5 Fans 77

4.5.1 Fan laws 78

4.5.2 Selection of fans 78

4.5.3 Calculation of ventilation fan duty 79

4.5.4 Pressure drop calculation 79

4.5.5 Energy efficiency in ventilation systems 81

4.6 Worked examples 82

4.7 Tutorial problems 91

4.8 Case Study: The National Trust’s ventilation system 92

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Contents vii

5 Heat Gains in Buildings 99

5.1 Introduction 100

5.2 Lighting 100

5.2.1 Lighting criteria 100

5.2.2 Lighting terminology 101

5.2.3 Measurement of light intensity 102

5.2.4 Types of lamp 102

5.3 Energy-saving measures for lighting 104

5.4 Casual heat gains from appliances 105

5.5 Occupants’ heat gains 106

5.6 Worked examples 106

5.7 Tutorial problems 110

5.8 Case Study: Calculation of heating load for

a building – options 111

6 Thermal Comfort 115

6.1 Thermal comfort in human beings 116

6.2 Energy balance of the human body 116

6.3 Latent heat losses 117

6.3.1 Heat loss by diffusion 118

6.3.2 Heat loss by evaporation 119

6.3.3 Heat loss by respiration 119

6.4 Sensible heat losses 119

6.4.1 Heat loss by conduction 120

6.4.2 Heat loss by convection 120

6.4.3 Heat loss by radiation 120

6.5 Estimation of thermal comfort 124

6.5.1 Determination of comfort temperature, PMV and PPD 124

6.6 Worked examples 125

6.7 Tutorial problems 131

7 Refrigeration, Heat Pumps and the Environment 133

7.1 Introduction 134

7.2 History of refrigeration 135

7.3 Refrigeration choice and environmental impact 136

7.3.1 TEWI calculation 139

7.4 Refrigeration system components 139

7.4.1 The compressor unit 140

7.4.2 The expansion valve 142

7.4.3 The condenser 144

7.4.4 The evaporator 145

7.5 Heat pump and refrigeration cycles 146

7.5.1 The heat engine 146

7.5.2 Reversed heat engine (heat pump/refrigerator) 147

7.5.3 Carnot refrigeration cycle 149

7.5.4 Simple refrigeration cycle 150

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viii Contents

7.5.5 Practical refrigeration cycle 150

7.5.6 Irreversibilities in the refrigeration cycle 152

7.5.7 Multi-stage compression 153

7.5.8 Multipurpose refrigeration systems with a single

compressor 155

7.6 Worked examples 156

7.7 Tutorial problems 164

7.8 Case Study: Star Refrigeration Ltd – heat pumps

in a chocolate factory. May 2010, UK 165

8 Design of Heat Exchangers 169

8.1 Types of heat exchanger 170

8.1.1 Double-pipe heat exchangers 170

8.1.2 Shell-and-tube heat exchangers 170

8.1.3 Cross-flow heat exchangers 170

8.2 Overall heat transfer coefficient 172

8.3 Analysis of heat exchangers 173

8.3.1 The logarithmic mean temperature

difference method 173

8.3.2 The F-method for analysis of heat exchangers 175

8.3.3 The effectiveness–NTU method for analysis

of heat exchangers 176

8.4 Optimisation of heat transfer surfaces (fins) 181

8.4.1 Fin types 181

8.4.2 Theory of fins 182

8.5 Worked examples 184

8.6 Tutorial problems 197

9 Instrumentation for Energy Management 201

9.1 Introduction 202

9.2 Temperature measurement 202

9.2.1 Expansion thermometers 202

9.2.2 Electrical resistance thermometers 205

9.2.3 Thermocouples 208

9.2.4 Change-of-state thermometers 209

9.2.5 Optical pyrometers 209

9.2.6 Infrared temperature sensors 210

9.2.7 Selection guides for temperature measurement 211

9.3 Humidity measurement 211

9.3.1 Wet and dry bulb hygrometer 211

9.3.2 Liquid-in-steel hygrometers 212

9.3.3 Electrical resistance hygrometer 213

9.3.4 Hair hygrometer 213

9.3.5 Thermal conductivity hygrometer 214

9.3.6 Capacitive humidity sensors 215

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Contents ix

9.4 Pressure measurement 216

9.4.1 Barometers 216

9.4.2 Bourdon pressure gauge 216

9.4.3 Pressure transducers 217

9.4.4 Manometers 218

9.5 Flow measurement 219

9.5.1 Flow measurement by collection 219

9.5.2 Flow measurement by rotameter 219

9.5.3 Flow measurement by turbine flow meter 219

9.5.4 Flow measurement by differential pressure

flow meter 220

9.5.5 Velocity and flow measured by anemometers 223

9.6 Electrical measurements 225

9.6.1 Energy in electrical circuits 225

9.6.2 Ohm’s law 225

9.6.3 Electrical power 225

9.6.4 Alternating current power 226

9.6.5 Electrical measurements 227

9.7 Worked examples 230

9.8 Tutorial problems 234

10 Renewable Energy Technology 235

10.1 Introduction 236

10.2 Solar energy 237

10.2.1 Solar declination 238

10.2.2 Solar altitude angle and azimuth angle 238

10.2.3 Solar time and angles 238

10.2.4 Solar radiation 239

10.2.5 Incidence angle 240

10.2.6 Fixed aperture 240

10.2.7 Solar tracking 241

10.2.8 The aperture intensity 241

10.2.9 Energy conversion efficiency 243

10.2.10 Installation of photovoltaic modules 243

10.2.11 Technology status 243

10.2.12 PV system components 245

10.3 Wind energy 248

10.3.1 Ideal wind power calculation 249

10.3.2 Theory of wind turbines 250

10.3.3 Wind turbine components 253

10.3.4 Types of wind turbine 253

10.4 Biomass 255

10.4.1 Sources of biomass 255

10.4.2 Combustion equation for biomass 257

10.5 Hydraulic turbines 258

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x Contents

10.5.1 Theory of hydraulic turbines 258

10.5.2 Fluid power 263

10.5.3 Classification of hydraulic turbines 264

10.5.4 Design and selection of hydraulic turbines 267

10.5.5 Relationship between specific speed and type

of hydraulic turbine 267

10.6 Worked examples 268

10.7 Tutorial problems 277

Appendix: Case Study: Energy audit for a school 279

Index 289

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xi

Preface

This book is concerned with the subject of energy: as a resource, its use and

the ways in which it can be optimised.

The need for this type of book is very well documented, and below I will try

to articulate that.

Coal fuelled the Industrial Revolution in the 18th and 19th centuries. It remained

as the prime fuel until well into the 20th century, supplying the steam engines

used in road vehicles and trains. The industrialised nations were in huge

competition in their search for additional fuels and the discovery of oil in the

Middle East and elsewhere extended the use of this fuel, opening up a broader

scope for applications. With the advent of the automobile, aeroplanes and the

spreading use of electricity, oil became the dominant fuel during the 20th century.

During the Arab–Israeli wars in 1967 and 1972, the price of oil increased from 5 to

45 US dollars per barrel and there was a resultant shift away from oil. Coal and

nuclear became the fuels of choice for electricity generation, and conservation

measures increased energy efficiency. The use of fossil fuels has continued to

grow and their share of the energy supply has increased. The more recent Gulf

Wars in the 1990s and the new millennium, and the accompanying invasion of

Iraq are, some would say, clear evidence of the importance of oil to the West.

In 2005, total worldwide energy consumption was 500 EJ (= 5 × 1020J or 138

900TWh) with 86.5% derived from the combustion of fossil fuels. Estimates of

the remaining worldwide energy resource vary, with the remaining fossil fuels

totalling an estimated 0.4 YJ (1 YJ = 1024J).

Political considerations over the security of supplies and environmental

concerns related to global warming and sustainability will move the world’s

energy consumption away from fossil fuels.

In order to drive the move away from fossil fuels, we are likely to witness

further examples of economic pressure through such measures as carbon

trading and green taxation. Some countries are taking action as a result of the

Kyoto Protocol, and further steps in this direction are proposed. For example,

the European Union Commission has proposed that the Energy Policy should

set a binding target of increasing the level of renewable energy in the EU’s

overall mix from less than 7% today to 20% by 2020.

This book tackles the fundamental principles of thermodynamics in day-to-

day engineering concepts; it provides the tools to measure process efficiency

and sustainability accurately in power and heating applications – helping

engineers to recognise why losses occur and how they can be reduced by

utilising familiar thermodynamic principles.

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xiii

Acknowledgements

I would like to express my appreciation and gratitude to the many people who

have put up with me through the period of writing this book; to all those who

offered support, read, wrote, offered comments, to those who assisted in the

editing, proofreading and design.

I wish to thank all of my students who have been with me over the course of

the years and helped me develop the material into its present form.

I would like to thank my family and friends and especially my son Mark who

helped me creating most of the illustrations and graphs in this book.

Grateful thanks are due to those who allowed me to present their case study

material in the various chapters of this book.

Last but not least, I beg the forgiveness of all others who have helped me

but I have failed to mention here.

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xv

Dimensions and Units

Any physical situation, whether it involves a single object or a complete

system, can be described in terms of a number of recognisable properties

which the object or system possesses. For example, a moving object could be

described in terms of its mass, length, area or volume, velocity and acceleration.

Its temperature or electrical properties might also be of interest, while other

properties – such as the density and viscosity of the medium through which it

moves – would also be of importance, since they would affect its motion. These

measurable properties used to describe the physical state of the body or

system are known as its variables; some variables are basic, such as length

and time, while others are derived, such as velocity. Each variable has units to

describe the magnitude of that quantity. Lengths in SI units are described in

units of metres. The metre is the unit of the dimension of length (L); hence, the

area will have dimension L2, and volume L3. Time (t) will have units of seconds;

hence, velocity is a derived quantity with dimensions of (Lt−1) and units of

metres per second (m/s or ms−1). A list of some variables together with their

units and dimensions is given in Table 1, while further examples of units and

conversion factors are given in Tables 2 to 7.

Definitions of some basic SI units

Mass: The kilogram is the mass of a platinum-iridium cylinder kept

at Sèvres in France.

Length: The metre is the distance between two engraved lines on a

platinum-iridium bar also kept at Sèvres. The measurement

is made at 0°C and standard atmospheric pressure, the bar

being supported in a specified manner. The metre is now

defined as being equal to 1 650 763.73 wavelengths in a

vacuum of the orange line emitted by the Krypton-86 atom.

Time: The second is defined as the fraction 1/31 556 925.975 of the

tropical year for 1900. The second is also declared to be the

interval occupied by 9 192 631 770 cycles of the radiation of

the caesium atom corresponding to the transition between

two closely spaced ground state energy levels.

Temperature: The Kelvin is the degree interval on the thermodynamic scale

on which the temperature of the triple point of water is

273.16 K exactly. (The temperature of the ice point is 273.15 K.)

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xvi Energy Audits

Definitions of some derived SI units

Force: The Newton is that force which, when acting on a mass of

one kilogram gives it an acceleration of one metre per second

per second.

Work energy, The joule is the work done by a force of one Newton when its

Quantity of point of application is moved through a distance of one metre

heat: in the direction of the force. The same unit is used for the

measurement of every kind of energy including quantity of

heat. The Newton metre, the joule and the watt second are

identical in value. It is recommended that the Newton is kept

for the measurement of torque or moment and the joule or

watt second is used for quantities of work or energy.

Table 1 Basic SI units.

Quantity Unit Symbol

Length [L] Metre MMass [m] Kilogram KgTime [t] Second SElectric current [I] Ampere ATemperature [T] Degree Kelvin KLuminous intensity [Iv] Candela Cd

Table 2 Derived units with special names.

Quantity Unit Symbol Derivation

Force [F] Newton N kg-m/s2

Work, energy [E] Joule J N-mPower [P] Watt W J/sPressure [p] Pascal Pa N/m2

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Table 3 Some examples of other derived SI units.

Quantity Symbol

Area m2

Volume m3

Density kg/m3

Angular acceleration rad/s2

Velocity m/sPressure, stress N/m2

Kinematic viscosity m2/sDynamic viscosity N-s/m2

Momentum kg-m/sKinetic energy kg-m2/s2

Specific enthalpy J/kgSpecifi c entropy J/kgK

Table 4 Non-SI units.

Quantity Unit Symbol Derivation

Time Minute min 60sTime Hour h 3.6 ksTemperature Degree Celsius °C K − 273.15Angle Degree ° π/180 radVolume Litre L 10−3 m3 or dm3

Speed Kilometre per hour km/h —Angular speed Revolution per

minuterev/min —

Frequency Hertz Hz cycle/sPressure Bar b 102 kN/m2

Kinematic viscosity Stoke St 100 mm2/sDynamic viscosity Poise P 100 mN-s/m2

Table 5 Multiples of units.

Name Symbol Factor Number

exa E 1018 1 000 000 000 000 000 000peta P 1015 1 000 000 000 000 000tera T 1012 1 000 000 000 000giga G 109 1 000 000 000mega M 106 1 000 000kilo k 103 1000hecto h 102 100deca da 10 10deci d 10−1 0.1centi c 10−2 0.01milli m 10−3 0.001micro μ 10−6 0.000001nano n 10−9 0.000000001pico p 10−12 0.000000000001fempto f 10−5 0.000000000000001atto a 10−18 0.000000000000000001

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xviii Energy Audits

Table 6 Conversion factors.

Item Conversion

Length 1 in = 25.4 mm1 ft = 0.3048 m1 yd = 0.9144 m1 mile = 1.609 km

Mass 1 lb = 0.4536 kg (0.453 592 37 exactly)Area 1 in2 = 645.2 mm2

1 ft2 = 0.092 90 m2

1 yd2 = 0.8361 m2

1 acre = 4047 m2

1 mile2 = 2.590 km2

Volume 1 in3 = 16.39 cm3

1 ft3 = 0.028 32 m3 = 28.32 litres1 yd3 = 0.7646 m3 = 764.6 litres1 UK gallon = 4.546 litres1 US gallon = 3.785 litres

Force, Weight 1 lbf = 4.448 NDensity 1 lb/ft3 = 16.02 kg/m3

Velocity 1 km/h = 0.2778 m/s1 ft/s = 0.3048 m/s1 mile/h = 0.4470 m/s = 1.609 km/h

Pressure, Stress 1000 Pa = 1000 N/m2 = 0.01 bar1 in H

2O = 2.491 mb

1 lbf/in2 (Psi) = 68.95 mb or 1 bar = 14.7 PsiPower 1 horsepower = 745.7 WMoment, Torque 1 ft-pdl = 42.14 mN-mRates of flow 1 gal/h = 1.263 ml/s = 4.546 L/h

1 ft3/s = 28.32 L/sFuel consumption 1 mile/gal = 0.3540 km/LKinematic viscosity 1 ft2/s = 929.0 cm2/s = 929.0 StDynamic viscosity 1 lbf-s/ft2 = 47.88 N-s/m2 = 478.8P

1 pdl-s/ft2 = 1.488 N-s/m2 = 14.88P1 cP = 1 mN-s/m2

Energy 1 horsepower-h = 2.685 MJ1 kW-h = 3.6 MJ1 Btu = 1.055 kJ1 therm = 105.5 MJ

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Dimensions and Units xix

Table 7 Conversion factors.Simply multiply the imperial by a constant factor to convert into metric or the other way around.

Unit ¥ Factor = Unit ¥ Factor = Unit

Length (L) ins 25.4 mm 0.0394 insft 0.305 m 3.281 ft

Area (A) in2 645.16 mm2 0.0016 in2

ft2 0.093 m2 10.76 ft2

Volume (V) in3 16.387 mm3 0.000061 in3

ft3 0.0283 m3 35.31 ft3

ft3 28.32 litre 0.0353 ft3

pints 0.5682 litre 1.7598 pintsImp. gal 4.546 litre 0.22 Imp galImp. gal 0.0045 m3 220 Imp gal

Mass (M) lb 0.4536 kg 2.2046 lb.tonne 1000 kg

Force (F) lb 4.448 N 0.2248 lb.Velocity (V) ft/min 0.0051 m/sec 196.85 ft/minVolume flow Imp gal/

min0.0758 litres/s 13.2 Imp gal/

minImp gal/h 0.00013 m3/s 7,936.5 Imp gal/hft3/min 0.00047 m3/s 2,118.6 ft3/min

Pressure (P) lb/in2 0.0689 bar 14.5 lb/in2

kg/cm2 0.9807 bar 1.02 kg/cm2

Density (r) Lb/ft3 16.019 kg/m3 0.0624 lb/ft3

Heat flow rate (Q) Btu/h 0.2931 W 3.412 Btu/hkcal/h 1.163 W 0.8598 kcal/h

Thermal conductivity (k)

Btu/ft h R 1.731 W/mK 0.5777 Btu/ft h Rkcal/m h K 1.163 W/mK 0.8598 kcal/m h K

Thermal conductance (U)

Btu/h ft2 R 5.678 W/m2K 0.1761 Btu/h ft2 Rkcal/h m2 K 1.163 W/m2K 0.8598 kcal/h m2 K

Enthalpy (h) Btu/lb. 2,326 J/kg 0.00043 Btu/lb.kcal/kg 4,187 J/kg 0.00024 kcal/kg

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xxi

List of Figures

1.1 Energy conversions in a typical coal-fired power plant. 7

1.2 The first wake-up call by Hubbert. 12

1.3 World’s energy consumption, past and forecast. 14

2.1 UK map showing degree-day regions. 27

2.2 Degree-day regression. 34

2.3 Energy Performance Certificate. 35

3.1 Conduction heat transfer. 47

3.2 Radial conduction. 48

3.3 Convection heat transfer. 49

3.4 Conduction through multiple layers. 52

3.5 Combined convection–conduction–convection heat transfer. 53

3.6 Radial conduction through multiple layers. 54

4.1 Forced ventilation systems. 75

4.2 Selection of fans. 78

4.3 The Moody diagram. 80

5.1 Visible light spectrum. 101

5.2 Light dissipation (inverse law). 102

6.1 Energy balance for the human body. 117

6.2 Heat flow across the skin/clothes. 119

6.3 PMV–PPD relationship. 124

7.1 Basic refrigeration system. 140

7.2 Pressure expansion valve (PEV). 142

7.3 Thermostatic expansion valve (TEV). 143

7.4 Electronic expansion valve (EEV). 144

7.5 Condensers and evaporators (heat exchangers). 145

7.6 Heat engine. 146

7.7 Heat pump/refrigerator. 147

7.8 Comparison between a heat engine, a heat pump and a refrigerator. 149

7.9 Ideal refrigeration cycle. 149

7.10 Simple refrigeration cycle. 151

7.11 Refrigerator with a heat exchanger. 151

7.12 Irreversibilities in the refrigeration cycle. 152

7.13 Two-stage compression with intercooler. 154

7.14 Two-stage compression with flash intercooling. 154

7.15 Fridge–freezer. 155

8.1 Types of double-pipe heat exchanger. 171

8.2 Shell-and-tube heat exchanger. 171

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xxii Energy Audits

8.3 Cross-flow heat exchangers. 172

8.4 Derivation of the log mean temperature difference (LMTD). 174

8.5 (a) Correction factors for shell-and-tube heat exchangers

(1 shell); 176

(b) correction factors for shell-and-tube heat exchangers

(2 shells); 176

(c) correction factor for cross-flow heat exchangers, one

fluid unmixed. 177

8.6 (a) NTU–effectiveness chart for parallel-flow heat exchangers; 179

(b) NTU–effectiveness chart for counter-flow heat exchangers; 179

(c) NTU–effectiveness chart for shell-and-tube heat exchangers; 180

(d) NTU–effectiveness chart for cross-flow heat exchangers; 180

(e) NTU–effectiveness for any heat exchanger with fluid

having a phase change. 181

8.7 Fin dimensions. 182

8.8 Efficiency of straight fins. 183

8.9 Efficiency of annular fins of rectangular profile. 184

9.1 Liquid-in-glass thermometer. 203

9.2 Dial for a liquid-in-steel thermometer. 204

9.3 Bi-metal thermometer. 204

9.4 Gas thermometer. 205

9.5 Platinum resistance thermometer and its circuit on the left. 206

9.6 Resistance–temperature curve for a platinum RTD. 207

9.7 Thermistor characteristics for a typical sensor. 207

9.8 Thermocouple. 208

9.9 Forehead phase change thermometer. 209

9.10 Optical pyrometer. 210

9.11 Infrared thermometer. 210

9.12 Sling wet and dry bulb hygrometer. 212

9.13 Mercury-in-steel wet and dry bulb hygrometer. 213

9.14 Electrical resistance wet and dry bulb direct-reading hygrometer. 214

9.15 Hair hygrometer. 214

9.16 Thermal conductivity hygrometer. 215

9.17 Capacitive humidity meter. 215

9.18 Fortin barometer. 217

9.19 Aneroid barometer. 217

9.20 Bourdon gauge – mechanism. 218

9.21 The U-tube manometer. 218

9.22 The inclined manometer. 219

9.23 Bucket and watch flow measurement. 220

9.24 Weigh tank flow measurement. 220

9.25 Rotameter. 221

9.26 Axial turbine meter. 221

9.27 Pitot static tube. 222

9.28 Orifice plate. 222

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List of Figures xxiii

9.29 Venturi meter. 223

9.30 Cup-type anemometer. 224

9.31 Vane anemometer. 224

9.32 Hot-wire anemometer. 224

9.33 Ohm’s law. 226

9.34 Resistive AC circuit. 227

9.35 Basic electrical measurement. 228

9.36 Electrical power measurement. 229

10.1 Solar definitions. 239

10.2 Solar angles for a tilted surface. 241

10.3 Solar energy for Stafford, UK. 244

10.4 Layout of a PV system. 245

10.5 PV cell performance curve. 246

10.6 PV cell performance curve. 247

10.7 Wind power development. 249

10.8 Ideal wind energy theory. 250

10.9 Betz limit on wind energy efficiency and its implications. 252

10.10 Wind energy system. 253

10.11 Typical wind turbine efficiencies. 254

10.12 Photosynthesis. 255

10.13 Inside a hydropower plant. 259

10.14 Conservation of mass of a fluid flowing in a duct/pipe. 259

10.15 Fluid power system. 264

10.16 Types of hydraulic turbine. 265

10.17 Characteristics of hydraulic turbines. 267

10.18 Specific speeds for hydraulic turbines. 268

A.1 Springhead Primary School. 280

A.2 Plot of energy consumption vs degree-days. 281

A.3 Annual gas consumption. 281

A.4 Annual electricity consumption. 282

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xxv

List of Tables

1.1 Energy conversion matrix. 8

1.2 Enthalpy ‘heat’ of combustion of elementary fuel matter. 9

1.3 Environmental impacts of fossil fuels. 11

1.4 World’s energy consumption: past, present and future. 13

1.5 Estimated energy reserves of the world. 14

2.1 Energy conversion factors. 26

2.2 Exposure factors. 28

2.3 Area conversion factors. 28

2.4 NPI calculation form. 30

2.5 Yardsticks for annual energy consumption of common

buildings. 31

2.6 ‘20-Year’ average degree-day data and collection areas. 32

3.1 U values for common types of construction. 56

3.2 Heating load for a typical building with no insulation. 58

3.3 Building Regulations – U values (W/m2K). 58

4.1 Composition of ‘clean’, dry atmospheric air. 71

4.2 Composition of typical respired air. 72

4.3 Recommended winter indoor temperatures for common

buildings. 72

4.4 Recommended air changes for common buildings. 73

5.1 Characteristics of electric lamps. 103

5.2 Typical casual heat sources. 106

6.1 Metabolic rates for different activity levels. 118

6.2 Clothing factors. 121

6.3 Sensible and latent heat losses for different human activities. 122

7.1 Comparative properties of some common refrigerants. 138

8.1 Typical fouling factors. 173

8.2 Typical overall heat transfer coefficients. 173

9.1 Freezing and boiling temperatures for typical liquids. 203

9.2 Properties of thermocouple pairs. 208

9.3 Electrical measurements. 225

10.1 Monthly and yearly average insolation in the UK. 242

10.2 Wind energy savings on gas emissions (BWEA). 249

10.3 Comparison of biomass with other fuels. 256

10.4 Biomass technology. 258

10.5 Typical obstruction losses in flow systems. 263

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xxvi Energy Audits

A.1 Total (kWh) of gas and electricity used for the school

year 2008. 280

A.2 NPI calculation form. 283

A.3 Summarised heat load calculations. 284

A.4 Improved heat loss calculations. 284

A.5 NPI form, recalculated. 285

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Energy Audits: A Workbook for Energy Management in Buildings, First Edition. Tarik Al-Shemmeri.© 2011 Blackwell Publishing Ltd. Published 2011 by Blackwell Publishing Ltd.

1

Learning outcomes

● Demonstrate the various forms of energy:

mechanical, electrical, chemical and nuclear

Knowledge and

understanding

● Evaluate the amount of energy for various types Analysis

● Solve problems associated with energy

conversion

Problem solving

● Distinguish between: potential and kinetic

energy, electrostatic and electromagnetic

energy, chemical and thermal energy, energy

from nuclear fission and nuclear fusion

Knowledge and

understanding

● Calculate the calorific value of fuels Analysis

● Calculate the combustion products of fuels Analysis

● Examine future world energy scenarios Reflections

● Practise further tutorial problems Problem solving

1.1 Introduction 2

1.2 Forms of energy 2

1.3 Energy conversion 6

1.4 The burning question 8

1.5 Environmental impact from fossil fuels 11

1.6 Energy worldwide 12

1.7 Energy and the future 13

1.8 Worked examples 15

1.9 Tutorial problems 19

1.10 Case Study: Future energy for the world 20

Chapter 1

Energy and the Environment

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2 Energy Audits

1.1 Introduction

It is necessary to appreciate that energy will be needed to modify the state of

any working environment and keep the conditions comfortable, whether by

providing warm or cool air.

Heating the air is a simple process of increasing its thermal energy and

consequently raising its temperature. Heating of air can be achieved either by

direct or indirect means: examples such as coal and gas fires represent the

direct forms of heating normally used in domestic situations; electrical resist-

ance heating elements provide an example of an indirect method because

electricity is produced elsewhere. Hot water radiators are also used to provide

indirect heating of indoor air.

Similarly, the process of cooling air, or reducing its thermal energy, is energy

driven.

Both cooling and heating require a further process. After being treated (i.e.

heated or cooled), the air has to be delivered to the space where it is needed,

and hence an electric fan is usually used to push the air from the apparatus

out into the room.

The following sections will discuss the various forms of energy, and how

energy can be converted from one form to another form which is convenient

for heating, cooling, etc.

This chapter will demonstrate the environmental impact of using different

fuels to provide energy for heating or electricity.

1.2 Forms of energy

We associate energy with devices whose inputs are fuel based, such as

electrical current, coal, oil or natural gas, and whose outputs involve movement,

heat or light.

The unit of energy is the Joule (J). The rate of producing energy is called

power, and this has the unit Joules per second (Js−1) or the Watt (W).

There are five forms of energy:

● mechanical energy;

● electrical energy;

● chemical energy;

● nuclear energy;

● thermal energy.

1.2.1 Mechanical energy

This type of energy is associated with the ability to perform physical work.

There are two forms in which this energy is found; namely potential energy

and kinetic energy.

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