An Introduction to Thermogeology
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About the Author xi
Preface to the First Edition xiii
Preface to the Second Edition xv
Acknowledgements xvii
1 An Introduction 1
1.1 Who should read this book? 2
1.2 What will this book do and not do? 2
1.3 Why should you read this book? 3
1.4 Thermogeology and hydrogeology 6
2 Geothermal Energy 11
2.1 Geothermal energy and ground source heat 11
2.2 Lord Kelvin's conducting, cooling earth 12
2.3 Geothermal gradient, heat flux and the structure of the earth 14
2.4 Internal heat generation in the crust 16
2.5 The convecting earth? 17
2.6 Geothermal anomalies 19
2.7 Types of geothermal system 27
2.8 Use of geothermal energy to produce electricity by steam turbines 28
2.9 Binary systems 28
2.10 Direct use 30
2.11 Cascading use 30
2.12 Hot dry rock systems [a.k.a. 'enhanced geothermal systems (EGS)'] 32
2.13 The 'sustainability' of geothermal energy and its environmental impact 35
2.14 And if we do not live in Iceland? 38
3 The Subsurface as a Heat Storage Reservoir 40
3.1 Specific heat capacity: the ability to store heat 41
3.2 Movement of heat 45
3.3 The temperature of the ground 51
3.4 Insolation and atmospheric radiation 55
3.5 Cyclical temperature signals in the ground 59
3.6 Geothermal gradient 61
3.7 Human sources of heat in the ground 65
3.8 Geochemical energy 69
3.9 The heat energy budget of our subsurface reservoir 70
3.10 Cyclical storage of heat 72
3.11 Manipulating the ground heat reservoir 74
4 What Is a Heat Pump? 79
4.1 Engines 81
4.2 Pumps 84
4.3 Heat pumps 85
4.4 The rude mechanics of the heat pump 88
4.5 Absorption heat pumps 91
4.6 Heat pumps for space heating 91
4.7 The efficiency of heat pumps 93
4.8 Air-sourced heat pumps 96
4.9 Ground source heat pumps 98
4.10 Seasonal performance factor (SPF) 99
4.11 GSHPs for cooling 100
4.12 Other environmental sources of heat 100
4.13 The benefits of GSHPs 101
4.14 Capital cost 104
4.15 Other practical considerations 107
4.16 The challenge of delivering efficient GSHP systems 108
4.17 Challenges: the future 109
4.18 Summary 112
5 Heat Pumps and Thermogeology: A Brief History and International Perspective 114
5.1 Refrigeration before the heat pump 115
5.2 The overseas ice trade 117
5.3 Artificial refrigeration: who invented the heat pump? 119
5.4 The history of the GSHP 121
5.5 The global energy budget: how significant are GSHPs? 129
5.6 Ground source heat: a competitor in energy markets? 132
6 Ground Source Cooling 133
6.1 Our cooling needs in space 133
6.2 Scale effects and our cooling needs in time 134
6.3 Traditional cooling 135
6.4 Dry coolers 136
6.5 Evaporation 138
6.6 Chillers/heat pumps 141
6.7 Absorption heat pumps 143
6.8 Delivery of cooling in large buildings 144
6.9 Dehumidification 145
6.10 Passive cooling using the ground 145
6.11 Active ground source cooling 147
6.12 An example of open-loop groundwater cooling 148
7 Options and Applications for Ground Source Heat Pumps 150
7.1 How much heat do I need? 150
7.2 Sizing a GSHP 156
7.3 Open-loop ground source heat systems 161
7.4 Closed-loop systems 173
7.5 Domestic hot water by ground source heat pumps? 191
7.6 Heating and cooling delivery in complex systems 195
7.7 Heat from ice 201
8 The Design of Groundwater-Based Open-Loop Systems 202
8.1 Common design flaws of open-loop groundwater systems 203
8.2 Aquifers, aquitards and fractures 203
8.3 Transmissivity 205
8.4 Confined and unconfined aquifers 206
8.5 Abstraction well design in confined and unconfined aquifers 208
8.6 Design yield, depth and drawdown 210
8.7 Real wells and real aquifers 215
8.8 Sources of information 217
8.9 Multiple wells in a wellfield 222
8.10 Hydraulic feedback in a well doublet 227
8.11 Heat migration in the groundwater environment 234
8.12 The importance of three-dimensionality 240
8.13 Mathematical reversibility 242
8.14 Sustainability: thermally balanced systems and seasonal reversal 243
8.15 Groundwater modelling 244
8.16 Examples of open-loop heating/cooling schemes 245
8.17 Further reading 246
9 Pipes, Pumps and the Hydraulics of Closed-Loop Systems 248
9.1 Our overall objective 251
9.2 Hydraulic resistance of the heat exchanger 252
9.3 The hydraulic resistance of pipes 253
9.4 Acceptable hydraulic losses 255
9.5 Hydraulic resistances in series and parallel 255
9.6 An example 256
9.7 Selecting pumps 262
9.8 Carrier fluids 265
9.9 Manifolds 271
9.10 Hydraulic testing of closed loops 275
9.11 Equipping a ground loop 277
10 Subsurface Heat Conduction and the Design of Borehole-Based Closed-Loop Systems 279
10.1 Rules of thumb? 279
10.2 Common design flaws 282
10.3 Subsurface heat conduction 283
10.4 Analogy between heat flow and groundwater flow 286
10.5 Carslaw, Ingersoll, Zobel, Claesson and Eskilson's solutions 289
10.6 Real closed-loop boreholes 294
10.7 Application of theory - an example 304
10.8 Multiple borehole arrays 313
10.9 Simulating cooling loads 321
10.10 Simulation time 322
10.11 Stop press 323
11 Horizontal Closed-Loop Systems 325
11.1 Principles of operation and important parameters 326
11.2 Depth of burial 327
11.3 Loop materials and carrier fluids 328
11.4 Ground conditions 329
11.5 Areal constraints 333
11.6 Geometry of installation 333
11.7 Modelling horizontal ground exchange systems 344
11.8 Earth tubes: air as a carrier fluid 351
12 Pond- and Lake-Based Ground Source Heat Systems 353
12.1 The physics of lakes 354
12.2 Some rules of thumb 356
12.3 The heat balance of a lake 357
12.4 Open-loop lake systems 365
12.5 Closed-loop surface water systems 367
12.6 Closed-loop systems - environmental considerations 371
13 Standing Column Wells 372
13.1 'Standing column' systems 372
13.2 The maths 376
13.3 The cost of SCWs 377
13.4 SCW systems in practice 379
13.5 A brief case study: Grindon Camping Barn 379
13.6 A final twist - the Jacob doublet well 381
14 Thinking Big: Large-Scale Heat Storage and Transfer 383
14.1 The thermal capacity of a building footprint 384
14.2 Simulating closed-loop arrays with balanced loads 385
14.3 A case study of a balanced scheme: car showroom, Bucharest 390
14.4 Balancing loads 392
14.5 Deliberate thermal energy storage - closed-loop borehole thermal energy storage (BTES) 395
14.6 Aquifer thermal energy storage (ATES) 398
14.7 UTES and heat pumps 403
14.8 Regional transfer and storage of heat 403
15 Thermal Response Testing 410
15.1 Sources of thermogeological data 410
15.2 Laboratory determination of thermal conductivity 411
15.3 The thermal response test (TRT) 412
15.4 The practicalities: the test rig 417
15.5 Test procedure 420
15.6 Sources of uncertainty 425
15.7 Non-uniform geology 426
15.8 Non-constant power input 426
15.9 Groundwater flow 427
15.10 Analogies with hydrogeology 428
15.11 Thermal response testing for horizontal closed loops 429
16 Environmental Impact, Regulation and Geohazards 432
16.1 The regulatory framework 432
16.2 Thermal risks 437
16.3 Hydraulic risks 444
16.4 Geotechnical risks 449
16.5 Contamination risks 451
16.6 Geochemical risks 453
16.7 Microbiological risks 454
16.8 Excavation and drilling risks 455
16.9 Decommissioning of boreholes 458
16.10 Promoting technology: subsidy 459
16.11 The final word 460
References 463
Study Question Answers 493
Symbols 503
Glossary 509
Units 515
Index 518
