Shallow Geothermal Energy: Theory and Application

Description

This book is the outcome of more than a decade of research and technical development activities at Spain’s Geological Survey (IGME) concerning shallow geothermal energy, which were pursued in collaboration with other public bodies and European entities. It presents a compilation of papers on the theoretical foundations of, and practical aspects needed to understand the thermal regime of the topmost subsoil, up to 400 m deep, and the exceptional properties that this underground environment offers, which make it the ideal thermal reservoir for heating, ventilation, and air conditioning (HVAC).  In the book’s first section, the basic theory of thermodynamics as applied to shallow geothermal energy, heat transfer and fluid mechanics in the geological porous medium is developed. The nature of the subsoil’s thermal regime in general and in the urban environment in particular is described. The second section introduces readers to the fundamental aspects of thermal installations equipped with geothermal heat pumps, describes the types of geothermal exchangers most commonly used, and reviews the techniques used to obtain the thermal parameters of the terrain. It also discusses the potential environmental impacts of shallow geothermal activity and corresponding management strategies, as well as the legal aspects of its regulation for the governance of shallow geothermal resources in the EU in general and Spain in particular. In closing, the book highlights examples of the methodologies’ applications, developed by IGME in the city of Zaragoza and the Canary Islands.  The theoretical foundations, systematics and concrete applications make the book a valuable reference source for hydrogeologists, engineers and specialized technicians alike. Contents About the Authors Abbreviations Symbols Superscripts Superscripts 1 Introduction 1.1 Background 1.2 Shallow Geothermal Energy 1.2.1 Geothermal Energy 1.2.2 Types and Classification of Geothermal Energy 1.2.3 Shallow Geothermal Energy 1.2.4 Brief History of Shallow Geothermal Energy References 2 Theoretical Background 2.1 Thermodynamic Principles 2.1.1 Concept of Energy 2.1.2 Temperature and Heat 2.1.3 Heat Transfer Mechanisms 2.1.4 First Law of Thermodynamics 2.1.5 Carnot Cycle 2.1.6 Second Law of Thermodynamics 2.1.7 Isoentropic Process 2.2 Heat Transfer 2.2.1 Porous Media and Its Approximation to a Continuous Media 2.2.2 Heat Conduction Mechanism 2.2.3 Heat Convection Mechanism 2.2.4 Hydrodynamic Heat Dispersion 2.2.5 Conduction–Convection-Heat Dispersion in a Porous Media 2.3 Parameters of Interest in Shallow Geothermal Energy 2.3.1 Thermal Conductivity (W m−1 K−1) 2.3.2 Thermal Resistivity R (K W−1) 2.3.3 Thermal Expansion (K−1) 2.3.4 Density (kg m−3) 2.3.5 Specific Heat Capacity c (J kg−1 K−1) 2.3.6 Thermal Diffusivity α (m2 s−1) 2.3.7 Viscosity µ (Pa s) 2.3.8 Reynolds Number Re (−) 2.3.9 Fourier Number Fo (−) 2.3.10 Peclet Number Pe (−) 2.3.11 Porosity φ (−) 2.4 Fluid Mechanics in Porous Media 2.4.1 Darcy’s Law 2.4.2 General Groundwater Flow Equation References 3 Underground Thermal Regime 3.1 Energy Balance of the Earth-Atmosphere System 3.2 Deep Geothermal Upward Heat Flow 3.2.1 Underground Temperature Profile 3.3 Regional Groundwater Flow and Heat Advection 3.4 Heat Exchange with Surface Water Bodies 3.5 Heat Exchange with Urban Structures References 4 Geothermal Heat Pump 4.1 Thermal Installations 4.1.1 External Heat Exchange Systems 4.1.2 Heat Production Systems 4.1.3 Heat Distribution Systems 4.1.4 Internal Heat Exchange Systems 4.2 Heat Pumps 4.3 Heat Transfer Through the Vapour Compression Cycle 4.3.1 Ideal Vapour Compression Cycle 4.3.2 Real Vapour Compression Cycle 4.4 Reversibility 4.5 Operating Mode of Heat Pumps 4.6 Performance 4.7 CO2 Emissions 4.8 Types of Heat Pumps 4.9 Geothermal Heat Pumps References 5 Shallow Geothermal Systems with Closed-Loop Geothermal Heat Exchangers 5.1 General Characteristics 5.2 Closed-Loop Geothermal Heat Exchangers 5.2.1 Types of Geothermal Heat Exchangers 5.2.2 Grids of Closed-Loop Geothermal Heat Exchangers (BHEs) 5.2.3 Drilling Systems in the Construction of Geothermal Heat Exchangers 5.3 Heat Transfer in Closed Geothermal Heat Exchangers 5.3.1 Heat Transfer Equation for Multicomponent Systems 5.3.2 General Heat Transfer Equation for Closed Geothermal Heat Exchangers 5.3.3 Heat Transfer Equations for the Main Closed Geothermal Heat Exchanger Designs 5.3.4 Analytical Models of Heat Transfer in Closed Geothermal Heat Exchangers 5.4 Heat Transfer with the Ground 5.4.1 Infinite Linear Source Model (ILS) 5.4.2 Infinite Cylindrical Source (ICS) Model 5.4.3 Finite Linear Source Model (FLS) 5.4.4 Moving Infinite Linear Source Model (MILS) 5.4.5 Numerical Models 5.5 Horizontal Closed-Loop Geothermal Heat Exchangers 5.5.1 Types of Horizontal Geothermal Heat Exchangers 5.6 Borehole Thermal Energy Storage (BTES) 5.7 Thermoactive Geostructures 5.7.1 Thermoactive Piles 5.7.2 Thermoactive Walls 5.7.3 Thermoactive Tunnels References 6 Shallow Geothermal Systems with Open-Loop Geothermal Heat Exchangers 6.1 Shallow Geothermal Installations with Open-Loop Geothermal Heat Exchangers 6.2 Components of an Open-Loop Geothermal Heat Exchanger 6.3 Design, Construction and Operation 6.4 Heat Transfer with the Ground 6.5 Chemical Quality of Groundwater 6.5.1 Reducing the Lifetime of Open-Loop Geothermal Heat Exchangers 6.6 Numerical Modelling of Groundwater Flow and Heat Transport 6.7 Aquifer Thermal Energy Storage (ATES) 6.7.1 Thermal Performance in ATES Systems 6.8 Thermal Use of Mine Water References 7 Obtaining Terrain Thermal Parameters 7.1 Estimation of Laboratory Thermal Parameters 7.1.1 Tests for the Estimation of Thermal Conductivity in the Laboratory 7.2 Thermal Response Test (TRT) 7.2.1 Performance of TRTs 7.2.2 Interpretation of Results Obtained from TRT Testing 7.3 Thermal Tracer Test (TTT) 7.4 Field Estimation of Hydraulic Parameters References 8 Environmental Impacts 8.1 Thermal Impacts 8.2 Geochemical Impacts 8.3 Ecological Impacts 8.4 Geotechnical Impacts References 9 Management and Governance of Shallow Geothermal Energy Resources 9.1 Management of Shallow Geothermal Energy Resources 9.1.1 Shallow Geothermal Energy Potential 9.1.2 Existing Management Approaches 9.1.3 Management Concepts 9.2 Governance Policies 9.3 Overall Structure of the Management Framework 9.3.1 Sustainable Development and Exploitation of Shallow Geothermal Energy Resources 9.3.2 Environmentally Friendly Use of Shallow Geothermal Energy Resources 9.3.3 Exploitation of Shallow Geothermal Resources in Coordination with Other Subsoil Uses 9.3.4 Effective Management of Shallow Geothermal Resources 9.4 Governance Model References 10 Legal Framework for Regulation 10.1 Policies, Strategies and Regulatory Standards in the European Union for the Promotion of Shallow Geothermal Energy 10.1.1 Policies and Strategies for the Promotion of Renewable Energies 10.1.2 Regulatory Standards for the Increase of Renewable Energies 10.2 European Regulatory Legal Framework for the Use of Shallow Geothermal Energy 10.2.1 Legal Framework at the National Level of Member States 10.2.2 European Regulatory Legal Framework for the Protection of the Groundwater Public Domain 10.3 Legal Framework for Regulation in Spain 10.3.1 Legal Definition of Shallow Geothermal Energy in Spain 10.3.2 Technical Guidelines for the Implementation of Good Practices 10.3.3 Regulations for the Use of Shallow Geothermal Installations 10.4 Special Requirements for the Installation and Operation of Shallow Geothermal Installations 10.5 Future Need for Adaptation of the Spanish Regulatory Framework References 11 Example of Application (I): The Management of Shallow Geothermal Energy Resources in the City of Zaragoza 11.1 The Early Exploitation of Shallow Geothermal Energy Resources 11.2 Geological and Hydrogeological Framework 11.3 Characterisation of Geothermal Exploitation 11.4 The Zaragoza Geothermal Monitoring Network 11.5 Impact of Thermal Discharges from Shallow Geothermal Installations on the Aquifer 11.5.1 Thermal Impact 11.5.2 Chemical Impact 11.5.3 Microbiological Impact 11.6 The 3D Numerical Model of Groundwater Flow and Heat Transport 11.7 Criteria and Policy for Adopted by Resource Managers 11.8 Current Situation. The Procedure for Authorisation of Thermal Discharges and Thermal Impact Assessment Studies 11.8.1 Authorisation Procedure for a Thermal Discharge References 12 Example of Application (II): The Exploitation of Shallow Geothermal Energy Resources in the Canary Islands 12.1 Renewable Energy in the Canary Islands 12.2 Shallow Geothermal Installations in the Canary Islands 12.2.1 Geological and Hydrogeological Framework 12.2.2 Impact of the Energy Transition Through Shallow Geothermal Energy 12.2.3 Environmental and Economic Benefits References