An Introduction to Thermogeology

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