Introduction to Thermogeology

David Banks is one of the Britain's leading hydrogeologists and has been instrumental in promoting ground source heating and cooling within the UK. He has over 26 years international experience from consultancy, the public sector, academia and commercial training. He runs his own business, Holymoor Consultancy Ltd., and has taught at the Universities of Sheffield, Leeds and Newcastle-upon-Tyne. Most recently, he has been a trainer on the EU's Geotrainet programme.

• About the Author xiPreface to the First Edition xiiiPreface to the Second Edition xvAcknowledgements xvii1 An Introduction 11.1 Who should read this book? 21.2 What will this book do and not do? 21.3 Why should you read this book? 31.4 Thermogeology and hydrogeology 62 Geothermal Energy 112.1 Geothermal energy and ground source heat 112.2 Lord Kelvin’s conducting, cooling earth 122.3 Geothermal gradient, heat flux and the structure of the earth 142.4 Internal heat generation in the crust 162.5 The convecting earth? 172.6 Geothermal anomalies 192.7 Types of geothermal system 272.8 Use of geothermal energy to produce electricity by steam turbines 282.9 Binary systems 282.10 Direct use 302.11 Cascading use 302.12 Hot dry rock systems [a.k.a. ‘enhanced geothermal systems (EGS)’] 322.13 The ‘sustainability’ of geothermal energy and its environmental impact 352.14 And if we do not live in Iceland? 383 The Subsurface as a Heat Storage Reservoir 403.1 Specific heat capacity: the ability to store heat 413.2 Movement of heat 453.3 The temperature of the ground 513.4 Insolation and atmospheric radiation 553.5 Cyclical temperature signals in the ground 593.6 Geothermal gradient 613.7 Human sources of heat in the ground 653.8 Geochemical energy 693.9 The heat energy budget of our subsurface reservoir 703.10 Cyclical storage of heat 723.11 Manipulating the ground heat reservoir 744 What Is a Heat Pump? 794.1 Engines 814.2 Pumps 844.3 Heat pumps 854.4 The rude mechanics of the heat pump 884.5 Absorption heat pumps 914.6 Heat pumps for space heating 914.7 The efficiency of heat pumps 934.8 Air-sourced heat pumps 964.9 Ground source heat pumps 984.10 Seasonal performance factor (SPF) 994.11 GSHPs for cooling 1004.12 Other environmental sources of heat 1004.13 The benefits of GSHPs 1014.14 Capital cost 1044.15 Other practical considerations 1074.16 The challenge of delivering efficient GSHP systems 1084.17 Challenges: the future 1094.18 Summary 1125 Heat Pumps and Thermogeology: A Brief History and International Perspective 1145.1 Refrigeration before the heat pump 1155.2 The overseas ice trade 1175.3 Artificial refrigeration: who invented the heat pump? 1195.4 The history of the GSHP 1215.5 The global energy budget: how significant are GSHPs? 1295.6 Ground source heat: a competitor in energy markets? 1326 Ground Source Cooling 1336.1 Our cooling needs in space 1336.2 Scale effects and our cooling needs in time 1346.3 Traditional cooling 1356.4 Dry coolers 1366.5 Evaporation 1386.6 Chillers/heat pumps 1416.7 Absorption heat pumps 1436.8 Delivery of cooling in large buildings 1446.9 Dehumidification 1456.10 Passive cooling using the ground 1456.11 Active ground source cooling 1476.12 An example of open-loop groundwater cooling 1487 Options and Applications for Ground Source Heat Pumps 1507.1 How much heat do I need? 1507.2 Sizing a GSHP 1567.3 Open-loop ground source heat systems 1617.4 Closed-loop systems 1737.5 Domestic hot water by ground source heat pumps? 1917.6 Heating and cooling delivery in complex systems 1957.7 Heat from ice 2018 The Design of Groundwater-Based Open-Loop Systems 2028.1 Common design flaws of open-loop groundwater systems 2038.2 Aquifers, aquitards and fractures 2038.3 Transmissivity 2058.4 Confined and unconfined aquifers 2068.5 Abstraction well design in confined and unconfined aquifers 2088.6 Design yield, depth and drawdown 2108.7 Real wells and real aquifers 2158.8 Sources of information 2178.9 Multiple wells in a wellfield 2228.10 Hydraulic feedback in a well doublet 2278.11 Heat migration in the groundwater environment 2348.12 The importance of three-dimensionality 2408.13 Mathematical reversibility 2428.14 Sustainability: thermally balanced systems and seasonal reversal 2438.15 Groundwater modelling 2448.16 Examples of open-loop heating/cooling schemes 2458.17 Further reading 2469 Pipes, Pumps and the Hydraulics of Closed-Loop Systems 2489.1 Our overall objective 2519.2 Hydraulic resistance of the heat exchanger 2529.3 The hydraulic resistance of pipes 2539.4 Acceptable hydraulic losses 2559.5 Hydraulic resistances in series and parallel 2559.6 An example 2569.7 Selecting pumps 2629.8 Carrier fluids 2659.9 Manifolds 2719.10 Hydraulic testing of closed loops 2759.11 Equipping a ground loop 27710 Subsurface Heat Conduction and the Design of Borehole-Based Closed-Loop Systems 27910.1 Rules of thumb? 27910.2 Common design flaws 28210.3 Subsurface heat conduction 28310.4 Analogy between heat flow and groundwater flow 28610.5 Carslaw, Ingersoll, Zobel, Claesson and Eskilson’s solutions 28910.6 Real closed-loop boreholes 29410.7 Application of theory – an example 30410.8 Multiple borehole arrays 31310.9 Simulating cooling loads 32110.10 Simulation time 32210.11 Stop press 32311 Horizontal Closed-Loop Systems 32511.1 Principles of operation and important parameters 32611.2 Depth of burial 32711.3 Loop materials and carrier fluids 32811.4 Ground conditions 32911.5 Areal constraints 33311.6 Geometry of installation 33311.7 Modelling horizontal ground exchange systems 34411.8 Earth tubes: air as a carrier fluid 35112 Pond- and Lake-Based Ground Source Heat Systems 35312.1 The physics of lakes 35412.2 Some rules of thumb 35612.3 The heat balance of a lake 35712.4 Open-loop lake systems 36512.5 Closed-loop surface water systems 36712.6 Closed-loop systems – environmental considerations 37113 Standing Column Wells 37213.1 ‘Standing column’ systems 37213.2 The maths 37613.3 The cost of SCWs 37713.4 SCW systems in practice 37913.5 A brief case study: Grindon Camping Barn 37913.6 A final twist – the Jacob doublet well 38114 Thinking Big: Large-Scale Heat Storage and Transfer 38314.1 The thermal capacity of a building footprint 38414.2 Simulating closed-loop arrays with balanced loads 38514.3 A case study of a balanced scheme: car showroom, Bucharest 39014.4 Balancing loads 39214.5 Deliberate thermal energy storage – closed-loop borehole thermal energy storage (BTES) 39514.6 Aquifer thermal energy storage (ATES) 39814.7 UTES and heat pumps 40314.8 Regional transfer and storage of heat 40315 Thermal Response Testing 41015.1 Sources of thermogeological data 41015.2 Laboratory determination of thermal conductivity 41115.3 The thermal response test (TRT) 41215.4 The practicalities: the test rig 41715.5 Test procedure 42015.6 Sources of uncertainty 42515.7 Non-uniform geology 42615.8 Non-constant power input 42615.9 Groundwater flow 42715.10 Analogies with hydrogeology 42815.11 Thermal response testing for horizontal closed loops 42916 Environmental Impact, Regulation and Geohazards 43216.1 The regulatory framework 43216.2 Thermal risks 43716.3 Hydraulic risks 44416.4 Geotechnical risks 44916.5 Contamination risks 45116.6 Geochemical risks 45316.7 Microbiological risks 45416.8 Excavation and drilling risks 45516.9 Decommissioning of boreholes 45816.10 Promoting technology: subsidy 45916.11 The final word 460References 463Study Question Answers 493Symbols 503Glossary 509Units 515Index 518