Table of Contents

Title Page

Preface

About the Authors

Acknowledgments

Nomenclature

Chapter 1: Introduction to Geothermal Energy

1.1 Features of Geothermal Energy
1.2 Geothermal Energy Systems
1.3 Outline of the Book
References

Chapter 2: Fundamentals

2.1 Introduction
2.2 Thermodynamics
2.3 Heat Transfer
2.4 Fluid Mechanics
2.5 The Nature of the Ground
References

Chapter 3: Background and Technologies

3.1 Introduction
3.2 Heat Pumps
3.3 Heat Exchangers
3.4 Heating, Ventilating, and Air Conditioning
3.5 Energy Storage

Chapter 4: Underground Thermal Energy Storage

4.1 Introduction
4.2 Thermal Energy Storage Methods
4.3 Underground Thermal Storage Methods and Systems
4.4 Integration of Thermal Energy Storage with Heat Pumps
4.5 Closing Remarks
References

Chapter 5: Geothermal Heating and Cooling

5.1 Ground-Source Heat Pumps
5.2 Geothermal Heat Exchangers
References

Chapter 6: Design Considerations and Installation

6.1 Sensitivity to Ground Thermal Conductivity
6.2 Thermal Response Test
6.3 Building Energy Calculations
6.4 Economics
6.5 Standards
References

Chapter 7: Modeling Ground Heat Exchangers

7.1 General Aspects of Modeling
7.2 Analytical Models
7.3 Numerical Modeling
7.4 Closing Remarks
References

Chapter 8: Ground Heat Exchanger Modeling Examples

8.1 Semi-Analytical Modeling of Two Boreholes
8.2 Numerical Modeling of Two Boreholes
8.3 Numerical Modeling of a Borefield
8.4 Numerical Modeling of a Horizontal Ground Heat Exchanger
8.5 Model Comparison
References

Chapter 9: Thermodynamic Analysis

9.1 Introduction
9.2 Analysis of an Underground Thermal Energy Storage System
9.3 Analysis of a Ground-Source Heat Pump System
9.4 Analysis of a System Integrating Ground-Source Heat Pumps and Underground Thermal Storage
References

Chapter 10: Environmental Factors

10.1 Introduction
10.2 Environmental Benefits
10.3 Environmental Impacts
References

Chapter 11: Renewability and Sustainability

11.1 Introduction
11.2 Renewability of Ground-Source Heat Pumps
11.3 Sustainability of Ground-Source Heat Pumps
References

Chapter 12: Case Studies

12.1 Introduction
12.2 Thermal Energy Storage in Ground for Heating and Cooling
12.3 Underground and Water Tank Thermal Energy Storage for Heating
12.4 Space Conditioning with Heat Pump and Seasonal Thermal Storage
12.5 Integrated System with Ground-Source Heat Pump, Thermal Storage, and District Energy
12.6 Closed-Loop Geothermal District Energy System
12.7 Closing Remarks
References

Appendix A: Numerical Discretization

Reference

Appendix B: Sensitivity Analyses

2.1 Parameters Affecting Thermal Interactions between Multiple Boreholes
2.2 Validation of the Two-Dimensional Numerical Solution with a Three-Dimensional Solution
2.3 Heat Flux Variation along Borehole Length
References

Index

End User License Agreement

List of Illustrations

Chapter 2: Fundamentals

Figure 2.1 An open system.
Figure 2.2 A closed system.
Figure 2.3 Schematic of an electrical generating plant.
Figure 2.4 Schematic of an electrical heat pump.
Figure 2.5 Illustrations of three modes of heat transfer: conduction (a); convection (b); and radiation (c).
Figure 2.6 Forced convection.
Figure 2.7 Natural convection.
Figure 2.8 Flow over various geometries. (a) External flow over a flat plate; (b) external crossflow over a cylinder; (c) internal flow through a pipe; (d) internal flow through a channel.
Figure 2.9 Laminar and turbulent flows.
Figure 2.10 Boundary layer in internal and external flows. (a) Formation of velocity boundary layer for internal flow between two flat plates; (b) formation of velocity boundary layer for external flow over a flat plate.
Figure 2.11 Ground temperature fluctuations with time for four values of depth z.

Chapter 3: Background and Technologies

Figure 3.1 Heat pump in the heating season.
Figure 3.2 Energy flows in space heating.
Figure 3.3 Energy flows in space cooling.

Chapter 4: Underground Thermal Energy Storage

Figure 4.1 Various advantages of utilizing thermal energy storage in energy systems compared with energy systems without thermal energy storage.
Figure 4.2 Various factors that determine the performance of a thermal energy storage unit.
Figure 4.3 Various types of sensible thermal energy storage. Ground-based storages are separated into shallow systems, which mainly utilize soil as a storage medium, and deep systems, which rely predominantly on rock as the storage medium.
Figure 4.4 Various factors that affect the economics of thermal energy storage systems.
Figure 4.5 Various common applications of thermal energy storage, broken down by sector.
Figure 4.6 Two of the many boreholes comprising the borehole thermal energy storage system at the University of Ontario Institute of Technology, Oshawa, Ontario, Canada. The composition and geology of the ground are shown. The U-tubes that act as ground heat exchangers are seen to split off a header and then to descend to the bottom of each borehole before returning to the top.
Figure 4.7 Energy system of the Drake Landing Solar Community in Okotoks, Alberta, Canada, showing the main system components and the primary flows of energy.
Figure 4.8 An electrically driven ground-source heat pump integrated with an aquifer thermal energy storage, showing both winter and summer operation modes. Heated fluid is extracted from the warm well in winter, while cooled fluid is extracted from the cold well in summer. The heat exchanger and heat pump are shown in winter mode, where they deliver heat for heating. In summer mode, however, the heat pump extracts heat from the space being cooled and rejects the heat via the heat exchanger to the warm well.
Figure 4.9 Operating strategies for a ground-source heat pump integrated with an aquifer thermal storage. (a) Heating; (b) cooling.
Figure 4.10 Borehole thermal energy storage system at the University of Ontario Institute of Technology, Oshawa, Ontario, Canada. The boreholes comprising the thermal energy storage system are located below the university quadrangle field, which is surrounded by university buildings.

Chapter 5: Geothermal Heating and Cooling

Figure 5.1 Ground-source heat pump installation growth from 1996 to 2008 in Canada.
Figure 5.2 Schematic of a two-stage heat pump and the heat exchanger providing an interface between the stages.
Figure 5.3 Horizontal ground heat exchangers.
Figure 5.4 Slinky ground heat exchanger.
Figure 5.5 Cross section of various types of vertical borehole heat exchangers.
Figure 5.6 Vertical ground heat exchanger.

Chapter 6: Design Considerations and Installation

Figure 6.1 Solution domain for a region of ground containing several borehole systems.
Figure 6.2 Heat flow rate at the borehole wall, per unit length of borehole.
Figure 6.3 Variation of the temperature of the borehole wall with time, for several values of the ground thermal conductivity $c06-math-001$ .
Figure 6.4 Ground temperatures outside of borefield boundary, for several values of ground thermal conductivity $c06-math-002$ , after (a) 3 months and (b) 9 months of system operation.
Figure 6.5 Ground temperatures contours after 3 months, for several values of ground thermal conductivity $c06-math-003$ .
Figure 6.6 Ground temperatures contours after 9 months, for several values of ground thermal conductivity $c06-math-004$ .
Figure 6.7 Average monthly air temperatures throughout the year for Toronto, Ontario, Canada.
Figure 6.8 Heating and cooling loads for a building in Belleville, IL, USA. (a) Heating load profile, (b) cooling load profile.
Figure 6.9 Transient ground temperature in response to (a) heat injection and (b) heat extraction. COP, coefficient of performance.
Figure 6.10 Variation of heating and cooling loads of the building throughout the year. Note that here positive values represent cooling loads and negative values represent heating loads (i.e., negative cooling loads).
Figure 6.11 Variation of heat flux on the ground heat exchanger wall with time for 1 year.
Figure 6.12 Typical balanced heat injection and extraction temporal profiles for 1 year.

Chapter 7: Modeling Ground Heat Exchangers

Figure 7.1 Cross section of vertical ground heat exchanger.
Figure 7.2 Thermal resistances in the borehole.
Figure 7.3 Ground temperatures (K) for a single borehole at time $c07-math-070$ months. (a) Temperature contours (K) of the analytical solution. (b) Comparison of the analytical and numerical solutions at $c07-math-071$ .
Figure 7.4 Comparison of the ground temperature (K) around multiple boreholes evaluated by analytical and numerical solutions at $c07-math-103$ at $c07-math-104$ months.
Figure 7.5 Ground temperature contours (K) of the analytical solution for multiple boreholes at time (a) $c07-math-105$ month and (b) $c07-math-106$ months.
Figure 7.6 Definition of geometric parameters $c07-math-118$ and $c07-math-119$ in Equation (7.33).
Figure 7.7 System geometric parameters for two boreholes at distances $c07-math-120$ and $c07-math-121$ from a fixed point in the surrounding ground.
Figure 7.8 Time varying heat transfer rates.

Chapter 8: Ground Heat Exchanger Modeling Examples

Figure 8.1 Schematic of (a) xz cross section of two boreholes installed at a borehole separation distance D_b, (b) xy cross section of two boreholes installed at a certain borehole distance, and (c) cross section of inside a borehole.
Figure 8.2 Distribution of heat flux along the borehole length.
Figure 8.3 Comparison of average borehole wall temperature along borehole length and borehole wall temperature at borehole mid-length (Z = 0.5).
Figure 8.4 Coupling procedure for borehole wall temperature and the model for inside the borehole to calculate the inlet and borehole outlet fluid temperatures according to the variable borehole wall temperature.
Figure 8.5 Boundary conditions in the example for two boreholes separated by a distance D_b.
Figure 8.6 Selection of the solution domain for two boreholes of length H separated by a distance D_b. The gray area is selected for modeling.
Figure 8.7 Computational triangular grids used in the solution domain in xy cross section.
Figure 8.8 Computational grids used in the solution domain in xz cross section.
Figure 8.9 Cell-centered control volume construction in two-dimensional unstructured meshes.
Figure 8.10 Illustration of algorithm used in the user defined function applied in the simulation.
Figure 8.11 Ground load profile for both boreholes in the current modeling example.
Figure 8.12 Solution procedure for modeling a domain consisting of multiple boreholes including the borehole fluid, grout, and ground in ANSYS FLUENT.
Figure 8.13 Solution domain. (a) Horizontal cross section (xy) and (b) horizontal cross section (xz).
Figure 8.14 Triangular mesh used for the solution domain.
Figure 8.15 Horizontal ground heat exchanger arrangements.
Figure 8.16 Variation of seasonal heating COP of the GSHP system with pipe length for a GHE at various depths.
Figure 8.17 Variation of seasonal cooling COP of a GSHP system with pipe length for a GHE at various depths.
Figure 8.18 Variation of overall COP of GSHP system with pipe length for a GHE at various depths.
Figure 8.19 Variation of total energy consumption of GSHP system with pipe length for a GHE at various depths.
Figure 8.20 Transient temperature of the borehole wall and borehole inlet and outlet fluid temperatures for numerical and analytical solutions.
Figure 8.21 Borehole fluid temperature profile along the borehole from numerical and analytical solutions. Z is defined in Equation (7.31).

Chapter 9: Thermodynamic Analysis

Figure 9.1 Temporal variations during experimental aquifer thermal energy storage test cycles of water temperature during charging (a) and discharging (b).
Figure 9.2 Temporal variations during experimental aquifer thermal energy storage test cycles of water volumetric flow rate during charging (a) and discharging (b).
Figure 9.3 Hybrid ground-source heat pump system.
Figure 9.4 Schematic of ground-source heat pump and borehole thermal energy storage system. Source: Adapted from Dincer and Rosen (2013) and Kizilkan and Dincer (2012).

Chapter 10: Environmental Factors

Figure 10.1 Annual temperature variations of the borehole wall.
Figure 10.2 Temperature contours in the ground surrounding 4 of the 16 boreholes in the system (the holes surrounded with the highest temperature gradient are shown in the figure) in Year 1. (Note that four boreholes are shown here due to symmetry.)
Figure 10.3 Ground temperature outside the borehole field after 10 months of system operation.
Figure 10.4 Borehole wall temperatures. (a) Borehole 1 and (b) Borehole 4.
Figure 10.5 Borehole wall temperatures of Borehole 1 and Borehole 4 over 5 years of system operation.
Figure 10.6 Temperature contours in the ground surrounding 4 of the 16 boreholes in the system (the holes surrounded with the highest temperature gradient shown in the figure) for Years 1–5. (Note that four boreholes are shown here due to symmetry.)

Chapter 11: Renewability and Sustainability

Figure 11.1 Heat pump COP_rev variations with time for (a) ground heating load and (b) ground cooling load.
Figure 11.2 Borehole wall temperature rise due to operation of a neighboring system for several values of borehole separation distances D_b.
Figure 11.3 Variation of coefficient of performance of a reversible heat pump with borehole fluid temperature in (a) heat delivery mode and (b) heat removal mode for several values of coil temperatures T_c.
Figure 11.4 Borehole wall temperature rise due to operation of a neighboring system borehole for a separation distance D_b of (a) 4 m and (b) 6 m.

Chapter 12: Case Studies

Figure 12.1 The network of water pipes with thermal energy storage for heating and cooling buildings (Anon. 1998).
Figure 12.2 Drake Landing Solar Community and its principal energy components. Source: Sibbitt et al. (2007). Reproduced with the permission of the Minister of Natural Resources Canada.
Figure 12.3 Row of Drake Landing Solar Community houses and garages covered with solar collectors. Source: Sibbitt et al. (2007). Reproduced with the permission of the Minister of Natural Resources Canada.
Figure 12.4 One of the two water-filled, short-term thermal storage tanks at the Drake Landing Solar Community, shown during construction of the Energy Centre in which it is located. Source: Sibbitt et al. (2007). Reproduced with the permission of the Minister of Natural Resources Canada.
Figure 12.5 Layout of the 52 houses in the Drake Landing Solar Community and its energy distribution system. Source: Sibbitt et al. (2007). Reproduced with the permission of the Minister of Natural Resources Canada.
Figure 12.6 Piping used in the Drake Landing Solar Community energy distribution system. Source: Sibbitt et al. (2007). Reproduced with the permission of the Minister of Natural Resources Canada.
Figure 12.7 Trenches used for the piping used in the Drake Landing Solar Community energy distribution system. Source: Sibbitt et al. (2007). Reproduced with the permission of the Minister of Natural Resources Canada.
Figure 12.8 Main components of the Drake Landing Solar Community Energy Centre (heat exchanger, the solar collector loop, two thermal storage tanks), with typical temperatures shown for heat transport fluids. Source: Sibbitt et al. (2007). Reproduced with the permission of the Minister of Natural Resources Canada.
Figure 12.9 Radial layout of the 144 boreholes in the borehole thermal energy storage at the Drake Landing Solar Community in 24 parallel circuits, each with six boreholes in series. Source: Sibbitt et al. (2007). Reproduced with the permission of the Minister of Natural Resources Canada.
Figure 12.10 Borehole thermal energy storage construction at the Drake Landing Solar Community, showing radial configuration of boreholes and the piping. Source: Sibbitt et al. (2007). Reproduced with the permission of the Minister of Natural Resources Canada.
Figure 12.11 U-shaped pipes that descend in each 35-m-deep borehole at the DLSC. Source: Sibbitt et al. (2007). Reproduced with the permission of the Minister of Natural Resources Canada.
Figure 12.12 Space conditioning system incorporating a heat pump with underground seasonal thermal storage using in the form of aquifer thermal energy storage, showing heating and cooling modes. Source: Adapted from IEA-HPC (1994).
Figure 12.13 View of borefield during the construction of university buildings and the borehole thermal energy storage system, showing the grid of borehole headers (black dots) and interconnecting piping.
Figure 12.14 Cross section of borehole and U-tube borehole heat exchanger.
Figure 12.15 Schematic flow diagram of the borehole thermal energy storage at the University of Ontario Institute of Technology.

Appendix B: Sensitivity Analyses

Figure B.1 Solution domain representing the ground surrounding (a) a single and (b) two boreholes, in a two-dimensional plane.
Figure B.2 Temperature of ground surrounding multiple boreholes at several values at time t at y=0 m.
Figure B.3 Ground temperature around multiple boreholes at t=6 months and D_b=3 m. (a) Temperature contours (K) of the analytical solution. (b) Comparison of the analytical and numerical solutions at y=0 m.
Figure B.4 Temperature of ground surrounding multiple boreholes at several borehole distances at y=0 m.
Figure B.5 Ground temperature around multiple boreholes at q′′=50 W/m² and t=6 months. (a) Temperature contours (K) of the analytical solution. (b) Comparison of the analytical and numerical solutions at y=0 m.
Figure B.6 Temperature of ground surrounding multiple boreholes for various values of heat flux (q′′) at the borehole wall.
Figure B.7 Ground temperature around multiple boreholes at q′′=5 and 15 W/m² and t=6 months. (a) Temperature contours (K) of the analytical solution. (b) Comparison of the analytical and numerical solutions at y=0 m.
Figure B.10 Ground temperature around multiple boreholes at q′′=10 W/m² and t=6 months, and comparison of the two- and three-dimensional solutions at various borehole depths.
Figure B.11 Ground temperature around multiple boreholes at q′′=10 W/m² and t=6 months, and temperature response of the ground at various borehole depths for the three-dimensional analysis.
Figure B.12 Ground temperature around multiple boreholes at q′′=20 W/m² and t=6 months, and temperature response of the ground at various borehole depths for the three-dimensional analysis.
Figure B.13 Ground temperature around multiple boreholes in the xz plane in t=6 months, at various distances from borehole wall for the variable heat flux model.
Figure B.14 Ground temperature around multiple boreholes in t=6 months, at various borehole depths for (a) the variable heat flux model and (b) the constant heat flux model.
Figure B.15 Comparison of ground temperature around multiple boreholes at t=6 months for variable heat flux (VHF) and constant heat flux models at (a) z=95 m and z=−95 m and (b) z=0 m.
Figure B.16 Ground temperature around multiple boreholes in t=6 months for line-source and numerical models at various borehole depths.

List of Tables

Chapter 2: Fundamentals

Table 2.1 Exergy, availability, and essergy
Table 2.2 Exergy and energy
Table 2.3 Common dimensionless heat transfer parameters

Chapter 4: Underground Thermal Energy Storage

Table 4.1 Characteristics for two main types of sensible thermal energy storage (TES)
Table 4.2 Principal processes in thermochemical energy storage
Table 4.3 Candidate materials for thermochemical energy storage, broken down by thermochemical reaction basis
Table 4.4 Factors to be considered in designing or selecting a thermal energy storage system for a given application, divided by category
Table 4.5 Selected characteristics of common sensible and latent thermal energy storage media
Table 4.6 Performance factors for the three main types of thermal energy storage
Table 4.7 Primary advantages and disadvantages for the three main types of thermal energy storage
Table 4.8 Characteristics for various types of underground thermal energy storage
Table 4.9 Comparison of energy use and greenhouse gas (GHG) emissions associated with heating (space and domestic hot water) for conventional homes and those in the Drake Landing Solar Community
Table 4.10 Design parameter values for heat pumps integrated the borehole thermal energy storage, broken down by heating and cooling mode, at University of Ontario Institute of Technology, Oshawa, Ontario, Canada

Chapter 5: Geothermal Heating and Cooling

Table 5.1 Qualitative comparison of ground- and air-source heat pumps, broken down by characteristic
Table 5.2 Distribution of different heat exchanger types based on number of installations in some Canadian provinces

Chapter 6: Design Considerations and Installation

Table 6.1 Ground thermal characteristics for four hypothetical compositions
Table 6.2 Dry-bulb temperature hours for an average year in Scott AFB, Belleville, IL, USA; period of record = 1967 to 1996
Table 6.3 Dry-bulb monthly temperature hours for an average year in Scott AFB, Belleville, IL, USA; period of record = 1967 to 1996
Table 6.4 Typical heat pump heating and cooling capacities at an air flow rate of 6000 CFM (2.8 m³/s)
Table 6.5 Sample of bin energy calculations for the month of July in Scott AFB, Belleville, IL, USA

Chapter 7: Modeling Ground Heat Exchangers

Table 7.1 Comparison of various methods for heat transfer analysis inside a borehole

Chapter 8: Ground Heat Exchanger Modeling Examples

Table 8.1 Physical properties and system specifications
Table 8.2 Thermal properties and geometric characteristics used in the model
Table 8.3 Energy (MWh) and performance data for a single-layer GHE of 600 m at various depths
Table 8.4 Energy (MWh) and performance data for a double-layer GHE of 500 m at various depths
Table 8.5 Energy (MWh) and performance data for a doubled horizontal pipe spacing (H = 1.0 m)

Chapter 9: Thermodynamic Analysis

Table 9.1 Temporal variations for aquifer thermal energy storage, during discharging, of charged, recovered and lost energy and exergy as well as energy and exergy efficiencies
Table 9.2 Normalized temporal variations for aquifer thermal energy storage, during discharging, of charged, recovered and lost energy and exergy
Table 9.3 Process data for material streams in the hybrid ground-source heat pump system and the reference environment
Table 9.4 Work and heat rates for the devices in the hybrid ground-source heat pump system
Table 9.5 Exergy destruction rates and efficiencies for the overall hybrid ground-source heat pump system and its devices
Table 9.6 Exergy destruction rates and relative irreversibilities for the overall integrated system and its main component groups
Table 9.7 Exergy efficiencies for the overall integrated system and its main component groups
Table 9.8 Variations in exergy destruction rates and efficiencies for the overall integrated system with selected design parameters

Chapter 11: Renewability and Sustainability

Table 11.1 Comparison of old and modern technology combinations for providing heating using heat pumps

Chapter 12: Case Studies

Table 12.1 Comparison of annual energy use (in GJ) for a Drake Landing Solar Community house and a conventional house, for space and domestic hot water heating
Table 12.2 Comparison of annual greenhouse gas emissions (in t) for a Drake Landing Solar Community house and a conventional house, for space and domestic hot water heating
Table 12.3 Comparison of annual energy use for a heat pump system with underground seasonal thermal energy storage and a conventional system
Table 12.4 Comparison of annual environmental emissions for a heat pump system with underground seasonal thermal energy storage and a conventional system
Table 12.5 Design parameter values for heat pumps
Table 12.6 Variation of coefficient of performance with heat pump supply temperature

Appendix B: Sensitivity Analyses

Table B.1 Thermal properties and geometric characteristics of the model
Table B.2 Thermal properties and geometric characteristics of the model

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Preface

Geothermal energy systems that provide heating and cooling using the ground are increasingly applied, and represent a technology that supports sustainable use of energy. Ground-source heat pumps, thermal energy storage and district energy are components of geothermal energy systems, and have been around for over 40 years and are widely applied. But they are also undergoing research and being improved continually, and advanced systems and components, as well as advanced understanding, are expected to be developed over the foreseeable future.

In this book, geothermal energy systems that utilize ground energy in conjunction with heat pumps to provide sustainable heating and cooling are described. Information on a range of topics is provided, from thermodynamic concepts to more advanced discussions on the renewability and sustainability of closed-loop geothermal energy systems. Numerous applications of such systems are also described. Theory and analysis are emphasized throughout, with detailed descriptions of models available for vertical geothermal heat exchangers.

The book also contains many references, including some related to books and articles on various aspects of geothermal systems that are not fully covered. Some links to websites with basic freeware for ground-source heat transfer modeling and building heating loads are referenced throughout the book.

The book is research oriented, thereby ensuring that new developments and advances in geothermal energy systems are covered.

The book is intended for use by advanced undergraduate or graduate students in several engineering disciplines such as mechanical engineering, chemical engineering, energy engineering, environmental engineering, process engineering and industrial engineering. Courses on geothermal energy systems or related courses such as heat exchangers, thermal energy storage or heat pumps that are often offered at the graduate level in Mechanical Engineering or related fields may find this book useful. The information included is sufficient for energy, environment and sustainable development courses. The book can also be used in research centers, institutes and labs focusing on the areas mentioned above, by related learned societies and professional associations, and in industrial organizations and companies interested in geothermal energy and its applications. Drillers and installers as well as regulatory agencies may also be interested in the book. Furthermore, the book offers a valuable and readable reference text source for anyone interested in learning about geothermal energy systems.

The book strives to provide clear information on ground-based geothermal systems and the many advances occurring in the field in a way that makes it understandable for students, practitioners, researchers and policy makers.

Various topics are covered, from fundamentals to advanced discussions on sustainability. Many applications are described, while theory and analysis are emphasized throughout. Detailed descriptions are provided of models for geothermal heat exchangers and heat pumps. The organization of the book is intended to help the reader build knowledge in a logical fashion while working through the book, and is as outlined here. Introductory material is included in the first two chapters, with an overview of geothermal energy as a source of energy and technologies that can harvest it described in Chapter 1, and fundamentals of thermofluid engineering disciplines related to geothermal energy systems provided in Chapter 2. Information on the main components of geothermal energy systems such as heat pumps, heat exchangers, heating, ventilating, and air conditioning equipment and energy storage units are provided in Chapter 3. The next five chapters form the heart of the book, with thermal energy storage being the focus of Chapter 4, geothermal heating and cooling forming the core of Chapter 5, and design and installation considerations for geothermal energy systems being the emphasis of Chapter 6. Extensive material is provided on modeling of ground heat exchangers and heat pumps, with the modeling of ground heat exchangers including a variety of models examined in Chapter 7 and the application of the models to various relevant examples presented in Chapter 8. The thermodynamic analysis of geothermal energy systems is the focus of Chapter 9. Extensive coverage is provided on environmental and sustainability factors, as these have become increasingly germane in recent years. Environmental factors related to geothermal energy systems are covered in Chapter 10 while their renewability and sustainability are examined in Chapter 11. To close, a range of case studies for geothermal energy systems is presented in Chapter 12 that illustrate the technologies, their applications and their advantages and disadvantages.

The main features of the book are:

comprehensive coverage of ground-based geothermal energy systems;
detailed descriptions and discussions of methods to determine potential environmental impacts of geothermal energy systems and their thermal interactions;
presentations of the most up-to-date information in the area;
suitability as a good reference for geothermal heat exchangers;
a research orientation to provide coverage of the state of the art and emerging trends and recent developments;
numerous illustrative examples and case studies;
clarity and simplicity of presentation of geothermal energy systems that use the ground.

We hope this book allows geothermal energy to be used more widely for the provision of heating and cooling services using the ground in a sustainable manner, using both existing and conventional equipment and systems as well as new and advanced technologies. The book aims to provide an enhanced understanding of the behaviours of heating and cooling systems in the form of ground-source heat pumps that exploit geothermal energy for sustainable heating and cooling of buildings, and enhanced tools for improving them. By exploiting the benefits of applying exergy methods to these ground-based energy systems, we believe they can be made more efficient, clean and sustainable, and help humanity address many of the challenges it faces.

October 2016

Marc A. Rosen and Seama Koohi-Fayegh

University of Ontario Institute of

Technology, Oshawa, Canada

About the Authors

Marc A. Rosen is a Professor at the University of Ontario Institute of Technology in Oshawa, Canada, where he served as founding Dean of the Faculty of Engineering and Applied Science. A former President of the Engineering Institute of Canada and the Canadian Society for Mechanical Engineering, he is a registered Professional Engineer in Ontario. He has served in many professional capacities, including Editor-in-Chief of several journals and a member of the Board of Directors of Oshawa Power and Utilities Corporation. He is an active teacher and researcher in energy, sustainability, geothermal energy and environmental impact. Much of his research has been carried out for industry, and he has written numerous books. He has worked for such organizations as Imatra Power Company in Finland, Argonne National Laboratory near Chicago, and the Institute for Hydrogen Systems near Toronto. He has received numerous awards and honours, including an Award of Excellence in Research and Technology Development from the Ontario Ministry of Environment and Energy, the Engineering Institute of Canada's Smith Medal for achievement in the development of Canada, and the Canadian Society for Mechanical Engineering's Angus Medal for outstanding contributions to the management and practice of mechanical engineering. He is a Fellow of the Engineering Institute of Canada, the Canadian Academy of Engineering, the Canadian Society for Mechanical Engineering, the American Society of Mechanical Engineers, the International Energy Foundation and the Canadian Society for Senior Engineers.

Seama Koohi-Fayegh is a Post-doctoral Fellow at the Department of Mechanical Engineering at the University of Ontario Institute of Technology in Oshawa, Canada. She received her PhD in Mechanical Engineering at the University of Ontario Institute of Technology under the supervision of Professor Marc A. Rosen. Her PhD thesis topic was proposed by the Ontario Ministry of Environment and focused on thermal sustainability of geothermal energy systems: system interactions and environmental impacts. She did her Master's degree in Mechanical Engineering (Energy Conversion) at Ferdowsi University of Mashhad, Iran, and worked on entropy generation analysis of condensation with shear stress on the condensate layer. Her thesis research won multiple awards at the school level and at the Iranian Society of Mechanical Engineering in 2009. Her research interests include heat transfer, sustainable energy systems and energy technology assessment.

Nomenclature

Greek Letters

Subscripts

0	initial, ambient or reference condition
A	centroid A
a	surroundings
adv	advective
ave	average
b	borehole
bal	balance
BHE	borehole heat exchanger
BW	BHE side water/glycol solution
c	cell; cooling; charging
CL	cooling load
comp	compressor
cond	condenser
CS	control surface
CV	control volume
CW	cooling water
d	discharging
dest	destruction
e	exit; evaporation, evapotranspiration, melting snow or sublimation; equivalent
evap	evaporator
ExpV	expansion valve
f	fluid; borehole fluid; final
f1	borehole fluid in inlet pipe
f2	borehole fluid in outlet pipe
FanCoil	fan coil
g	grout; ground
H	high-temperature; heating; high
h	convective; heating
HL	heating load
i	initial; inlet; inner; ith borehole; ground discretization designation in r direction; ith time step
in	inlet
L	low-temperature; low
L	liquid water
lo	long-wave radiation
max	maximum
n	normal
nb	node number of adjacent cell
o	outdoor; overall; reference-environment state
out	outlet
P	centroid P
p	pipe
pump	pump
PHX	plate heat exchanger
r	radiation; in radial direction
rev	reversible
s	surface; ground
sn	shortwave radiation
sys	system
t	threshold
valve	valve
z	in axial direction
ϑ	in circumferential direction

Superscripts

.	rate with respect to time
0	previous time step
n	polytropic exponent; discretization step designation in time

Abbreviations

ASHP	air-source heat pump
ASHRAE	American Society for Heating, Refrigerating and Air-conditioning Engineers
BHE	borehole heat exchanger
BTES	borehole thermal energy storage
DLSC	Drake Landing Solar Community
GHE	ground heat exchanger
GHG	greenhouse gas
GSHP	ground-source heat pump
HGHE	horizontal ground heat exchanger
HP	heat pump
HVAC	heating, ventilating, and air conditioning
IEA	International Energy Agency
O	order
PCM	phase-change material
SUP	supplementary
TES	thermal energy storage
TRT	thermal response test
VGHE	vertical ground heat exchanger
ϵ-NTU	effectiveness-number of transfer units

A	surface area; m²; cross-sectional area, m²
a	absorptivity; temperature coefficient; constant
b	constant
Bi	Biot number
C	volumetric heat capacity of soil, J/m³ K
c	specific heat, J/kg K
COP	coefficient of performance
c_p	specific heat at constant pressure, J/kg K
c_v	specific heat at constant volume, J/kg K
d	diameter, m
dA	surface element, m²
d_i	pipe inner diameter, m
D	pipe diameter, m; uppermost part of the borehole, m; U-tube leg half distance, m
D_b	borehole separation distance, m
D_ϑ	isothermal moisture diffusivity, m²/s
E	energy, kJ; electrical energy, kJ
e	specific energy, J/kg
Ex	exergy, kJ
ex	specific exergy (flow or non-flow), kJ/kg
Ex^Q	exergy transfer associated with heat transfer, kJ
$c01-math-001$	exergy rate, kW
Ex_dest	exergy destruction (irreversibility), kJ
$c01-math-002$	exergy destruction rate (irreversibility rate), kW
F	force, N
f	fraction
Fo	Fourier number
Gr	Grashof number
Gz	Graetz number
g	gravitational acceleration, m/s²
H	overall heat transfer coefficient, W/m² K; active borehole length, m
$c01-math-003$	dimensionless parameter [Equation (7.28)]
h	specific enthalpy, kJ/kg; heat transfer coefficient, W/m² K; borehole distance from coordinate center, m
h_i	heat transfer coefficient of circulating fluid, W/m² K
h_z	depth where borehole heating starts, m
J₀	Bessel function of the first kind, order 0
J₁	Bessel function of the first kind, order 1
K_h	hydraulic conductivity, m/s
k	adiabatic exponent; thermal conductivity, W/m K; ground thermal conductivity, W/m K
k_b	grout thermal conductivity, W/m K
L	length scale, m; latent heat of vaporization of water, J/kg
L_s	leg spacing of U-tube, m
l	position of borehole in x coordinate, m
m	mass, kg
$c01-math-004$	mass flow rate, kg/s; borehole fluid mass flow rate, kg/s
M	molecular weight, kg/mol
n	number of moles, mol; number of time steps
NTU	number of transfer units
Nu	Nusselt number
P, p	pressure, Pa; dimensionless parameter [Equation (7.22)]
Pe	Peclet number
Pr	Prandtl number
Q	heat transfer, J
$c01-math-005$	heat transfer rate, W
q	thermal radiation rate, W
$c01-math-006$	heat flow rate per unit length of borehole, W/m
$c01-math-007$	heat flow rate per unit length of inlet pipe, W/m
$c01-math-008$	heat flow rate per unit length of outlet pipe, W/m
$c01-math-009$	heat flux at borehole wall, W/m²
$c01-math-010$	generated heat per unit volume, W/m³
R	gas constant, J/kg K; thermal resistance, m K/W
$c01-math-011$	universal gas constant, 8.314 kJ/mol K; dimensionless parameter [Equation (7.29)]
Ra	Rayleigh number
Re	Reynolds number
R₁₁	thermal resistance between the inlet pipe and the borehole wall, m K/W
R₁₂	thermal resistance between the inlet and outlet pipes, m K/W
R₂₂	thermal resistance between the outlet pipe and the borehole wall, m K/W
$c01-math-012$	thermal resistance between Pipe 1 and borehole wall, m K/W [Equation (7.18)]
$c01-math-013$	thermal resistance between Pipe 2 and borehole wall, m K/W [Equation (7.18)]
$c01-math-014$	thermal resistance between Pipes 1 and 2, m K/W [Equation (7.18)]
R_b2	thermal resistance between circulating fluid and borehole wall based on two-dimensional analysis, m K/W
R_b3	thermal resistance between circulating fluid and borehole wall based on three-dimensional analysis, m K/W
R_g	thermal resistance of conduction in grout, m K/W
R_p	thermal resistance of conduction in pipe, m K/W
R_s	ratio of ground heat extraction to ground heat injection
r	reflectivity; radial scale, m; radial coordinate, m
r^*	direction perpendicular to U-tube surface
r^**	radial distance from borehole axis
r₁	distance of point (x,y) in soil around multiple boreholes from Borehole 1, m
r₂	distance of point (x,y) in soil around multiple boreholes from Borehole 2, m
r_b	borehole radius, m
r_i	pipe inner radius, m
r_p	pipe radius, m
S	entropy, kJ/K
s	specific entropy, kJ/kg K
St	Stanton number
S_φ	source of φ per unit volume
T	temperature, K or °C
$c01-math-015$	temperature of borehole fluid entering U-tube, K
$c01-math-016$	temperature of borehole fluid exiting U-tube, K
t	transmissivity; time, s
t_s	steady-state time, s
Δt	time step, s
U, u	velocity, m/s
u	specific internal energy, kJ/kg; velocity in x direction, m/s
V	volume, m³; velocity, m/s
$c01-math-017$	volumetric flow rate, m³/s
v	specific volume, m³/kg; kinematic viscosity, m²/s; velocity in y direction, m/s; velocity, m/s
$c01-math-018$	molar volume, m³/mol
v₀	velocity of borehole fluid, m/s
W	shaft work, J
$c01-math-019$	work rate or power, kW
w	velocity in z direction, m/s; position of borehole in y coordinate, m
x	x coordinate, m
Y	characteristic length, m
Y₀	Bessel function of the second kind, order 0
Y₁	Bessel function of the second kind, order 1
y	y coordinate, m
Z	dimensionless depth [Equation (7.22)]
z	axial coordinate, m; depth, m
$c01-math-020$	differential operator, del

α	thermal diffusivity, m²/s
β	dimensionless parameter [Equation (7.22)]
β₀	shape factor of grout resistance [Equation (7.10)]
β₁	shape factor of grout resistance [Equation (7.10)]
$c01-math-021$	diffusion coefficient for φ
γ	Euler's constant, 0.5772
▵	difference
$c01-math-022$	distance between centroids A and P of two neighboring grids, m
ϵ	emissivity; heat exchanger effectiveness; heat transfer efficiency of borehole; phase conversion factor
η	energy efficiency
Θ	dimensionless temperature [Equation (7.22)]
ϑ	volumetric moisture content (dimensionless); temperature difference relative to ground initial temperature, K; parameter
ϑ_l	volumetric liquid content (dimensionless)
μ	chemical potential, J/mol; dynamic viscosity, N s/m²
ρ	density, kg/m³
σ	Stefan–Boltzmann constant, 5.669 × 10⁻⁸ W/m² K⁴
τ_i	time at which step heat flux q_i is applied, s
Φ	scalar quantity
ϕ	circumferential coordinate, rad
ψ	exergy efficiency

Sustainable Heating and Cooling Using the Ground

Greek Letters

Subscripts

Superscripts

Abbreviations