Energy Audits
A Workbook for Energy Management in Buildings
1. Auflage September 2011
320 Seiten, Softcover
Wiley & Sons Ltd
ISBN:
978-0-470-65608-2
John Wiley & Sons
Energy efficiency is today a crucial topic in the built environment - for both designers and managers of buildings. This increased interest is driven by a combination of new regulations and directives within the EU and worldwide to combat global warming.
All buildings now must now acquire and display an EPC (energy performance certificate), a rating similar to the A-G rating given to white goods. But in order to understand how to be more efficient in energy use, you need first to understand the mechanisms of both energy requirements and how energy is used in buildings.
Energy Audits: a workbook for energy management in buildings tackles the fundamental principles of thermodynamics through day-to-day engineering concepts and helps students understand why energy losses occur and how they can be reduced. It provides the tools to measure process efficiency and sustainability in power and heating applications, helping engineers to recognize why energy losses occur and how they can be reduced utilizing familiar thermodynamic principles.
The author describes the sources of energy available today; explains how energy is used in buildings - and how energy is lost - and how this can be controlled and reduced. Investments in energy efficiency are considered for a number of case studies conducted on real buildings
The book explains the theory; illustrates it with case studies and worked examples; and then tests students' understanding with tutorial problems. This is an invaluable resource for students on engineering and building courses where energy management is now a core topic.
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
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
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
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
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
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
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
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
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
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
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
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
Tarik Al-Shemmeri is Professor of Renewable Energy Technology, Faculty of Computing, Engineering & Technology, Staffordshire University. He teaches energy management at both MSc and BEng/MEng levels and researches renewable energy technology.
