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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Comprehensively covers geothermal energy systems that utilize ground energy in conjunction with heat pumps to provide sustainable heating and cooling
The book describes geothermal energy systems that utilize ground energy in conjunction with heat pumps and related technologies to provide heating and cooling. Also discussed are methods to model and assess such systems, as well as means to determine potential environmental impacts of geothermal energy systems and their thermal interaction. The book presents the most up-to-date information in the area. It provides material on a range of topics, from thermodynamic concepts to more advanced discussions of the renewability and sustainability of geothermal energy systems. Numerous applications of such systems are also provided.
Geothermal Energy: Sustainable Heating and Cooling Using the Ground takes a research orientated approach to provide coverage of the state of the art and emerging trends, and includes numerous illustrative examples and case studies. Theory and analysis are emphasized throughout, with detailed descriptions of models available for vertical and horizontal geothermal heat exchangers.
Key features:
- Explains geothermal energy systems that utilize ground energy in conjunction with heat pumps to provide heating and cooling, as well as related technologies such as thermal energy storage.
- Describes and discusses methods to model and analyze geothermal energy systems, and to determine their potential environmental impacts and thermal interactions.
- Covers various applications of geothermal energy systems.
- Takes a research orientated approach to provide coverage of the state of the art and emerging trends.
- Includes numerous illustrative examples and case studies.
The book is key for researchers and practitioners working in geothermal energy, as well as graduate and advanced undergraduate students in departments of mechanical, civil, chemical, energy, environmental, process and industrial engineering.
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Veröffentlichungsjahr: 2016
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Table of Contents
Title Page
Copyright
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
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Guide
Table of Contents
Preface
Begin Reading
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 .
Figure 6.4 Ground temperatures outside of borefield boundary, for several values of ground thermal conductivity , 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 .
Figure 6.6 Ground temperatures contours after 9 months, for several values of ground thermal conductivity .
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 months. (a) Temperature contours (K) of the analytical solution. (b) Comparison of the analytical and numerical solutions at .
Figure 7.4 Comparison of the ground temperature (K) around multiple boreholes evaluated by analytical and numerical solutions at at months.
Figure 7.5 Ground temperature contours (K) of the analytical solution for multiple boreholes at time (a) month and (b) months.
Figure 7.6 Definition of geometric parameters and in Equation (7.33).
Figure 7.7 System geometric parameters for two boreholes at distances and 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/m
2
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/m
2
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/m
2
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/m
2
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/m
2
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 m
3
/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
Geothermal Energy
Sustainable Heating and Cooling Using the Ground
Marc A. Rosen and Seama Koohi-Fayegh
University of Ontario Institute of Technology, Oshawa, Canada
This edition first published 2017
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Library of Congress Cataloging-in-Publication Data
Names: Rosen, Marc (Marc A.), author. | Koohi-Fayegh, Seama, 1983- author.
Title: Geothermal energy : sustainable heating and cooling using the ground /
Marc A. Rosen and Seama Koohi-Fayegh, University of Ontario Institute of
Technology, Oshawa, Canada.
Description: Chichester, West Sussex, United Kingdom : John Wiley & Sons,
Inc., [2017] | Includes bibliographical references and index.
Identifiers: LCCN 2016037031 (print) | LCCN 2016046782 (ebook) | ISBN
9781119180982 (cloth) | ISBN 9781119181033 (pdf) | ISBN 9781119181019
(epub)
Subjects: LCSH: Ground source heat pump systems.
Classification: LCC TH7417.5 .R67 2017 (print) | LCC TH7417.5 (ebook) | DDC
697/.7–dc23
LC record available at https://lccn.loc.gov/2016037031
A catalogue record for this book is available from the British Library.
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.
Acknowledgments
The work of many of our colleagues helped greatly in the development of this book, and is gratefully acknowledged. Some of the material in this book is derived from research that we have carried out with numerous distinguished collaborators over the years. These include the following faculty members in geothermal energy and related areas:
Drs Ibrahim Dincer and Bale V. Reddy, University of Ontario Institute of Technology, Oshawa, Ontario, Canada
Drs Wei Leong and Alan Fung, Ryerson University, Toronto, Ontario, Canada
Dr Vlodek R. Tarnawski, Saint Mary's University, Halifax, Nova Scotia, Canada
Dr Robert A. Schincariol, Western University, London, Ontario, Canada
Dr Tomasz Śliwa, AGH University of Science and Technology, Krakow, Poland
Dr Frank C. Hooper, University of Toronto, Toronto, Ontario, Canada
Dr David S. Scott, University of Victoria, Victoria, British Columbia, Canada
We highly appreciate all of their efforts, as well as their thought-provoking insights.
Last but not least, the authors warmly thank their families, for their endless encouragement and support throughout the completion of this book. Their patience and understanding is most appreciated.
Nomenclature
A
surface area; m
2
; cross-sectional area, m
2
a
absorptivity; temperature coefficient; constant
b
constant
Bi
Biot number
C
volumetric heat capacity of soil, J/m
3
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, m
2
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, m
2
/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
exergy rate, kW
Ex
dest
exergy destruction (irreversibility), kJ
exergy destruction rate (irreversibility rate), kW
F
force, N
f
fraction
Fo
Fourier number
Gr
Grashof number
Gz
Graetz number
g
gravitational acceleration, m/s
2
H
overall heat transfer coefficient, W/m
2
K; active borehole length, m
dimensionless parameter [Equation (7.28)]
h
specific enthalpy, kJ/kg; heat transfer coefficient, W/m
2
K; borehole distance from coordinate center, m
h
i
heat transfer coefficient of circulating fluid, W/m
2
K
h
z
depth where borehole heating starts, m
J
0
Bessel function of the first kind, order 0
J
1
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
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
heat transfer rate, W
q
thermal radiation rate, W
heat flow rate per unit length of borehole, W/m
heat flow rate per unit length of inlet pipe, W/m
heat flow rate per unit length of outlet pipe, W/m
heat flux at borehole wall, W/m
2
generated heat per unit volume, W/m
3
R
gas constant, J/kg K; thermal resistance, m K/W
universal gas constant, 8.314 kJ/mol K; dimensionless parameter [Equation (7.29)]
Ra
Rayleigh number
Re
Reynolds number
R
11
thermal resistance between the inlet pipe and the borehole wall, m K/W
R
12
thermal resistance between the inlet and outlet pipes, m K/W
R
22
thermal resistance between the outlet pipe and the borehole wall, m K/W
thermal resistance between Pipe 1 and borehole wall, m K/W [Equation (7.18)]
thermal resistance between Pipe 2 and borehole wall, m K/W [Equation (7.18)]
thermal resistance between Pipes 1 and 2, m K/W [Equation (7.18)]
R
b
2
thermal resistance between circulating fluid and borehole wall based on two-dimensional analysis, m K/W
R
b
3
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
r
1
distance of point (
x
,
y
) in soil around multiple boreholes from Borehole 1, m
r
2
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
temperature of borehole fluid entering U-tube, K
temperature of borehole fluid exiting U-tube, K
t
transmissivity; time, s
t
s
steady-state time, s
Δ
t
time step, s
U, u
velocity, m/s
u
specific internal energy, kJ/kg; velocity in
x
direction, m/s
V
volume, m
3
; velocity, m/s
volumetric flow rate, m
3
/s
v
specific volume, m
3
/kg; kinematic viscosity, m
2
/s; velocity in
y
direction, m/s; velocity, m/s
molar volume, m
3
/mol
v
0
velocity of borehole fluid, m/s
W
shaft work, J
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
Y
0
Bessel function of the second kind, order 0
Y
1
Bessel function of the second kind, order 1
y
y
coordinate, m
Z
dimensionless depth [Equation (7.22)]
z
axial coordinate, m; depth, m
differential operator, del
Greek Letters
α
thermal diffusivity, m
2
/s
β
dimensionless parameter [Equation (7.22)]
β
0
shape factor of grout resistance [Equation (7.10)]
β
1
shape factor of grout resistance [Equation (7.10)]
diffusion coefficient for φ
γ
Euler's constant, 0.5772
▵
difference
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/m
2
ρ
density, kg/m
3
σ
Stefan–Boltzmann constant, 5.669 × 10
−8
W/m
2
K
4
τ
i
time at which step heat flux
q
i
is applied, s
Φ
scalar quantity
ϕ
circumferential coordinate, rad
ψ
exergy efficiency
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
f
1
borehole fluid in inlet pipe
f
2
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;
i
th borehole; ground discretization designation in
r
direction;
i
th 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
Chapter 1Introduction to Geothermal Energy
Geothermal energy systems are one option for providing energy services. They take advantage of the ground and the energy it contains. Sometimes ground energy is the basic ground at its natural temperature, which is mainly affected by ambient conditions. At other times, the ground is at an elevated temperature. Considering the current level of geothermal energy use and future energy needs, geothermal energy sources show great potential for contributing a larger fraction of the world's energy needs.
Archaeological evidence shows that geothermal energy was first used by ancient peoples, including the Romans, Chinese, and Native Americans. They used hot mineral springs as a source of heat for bathing, cooking, and heating. The minerals in water from these springs also served as a source of healing. While such uses of hot springs have changed over time, they are still used as a source of heat for bathing in several spas around the world. With technological developments, the use of geothermal energy has expanded to deeper levels of the earth's crust, which can be used for a wider range of applications such as domestic heating and cooling, industrial processes, and electricity generation. However, only a small fraction of available geothermal energy is currently used commercially to generate electricity or provide useful heating, in part due to the current state of the technology.
Geothermal energy systems that exploit hot reservoirs in the ground (e.g., thermal springs, geysers, ground heated by hot magma) are used mainly to generate electricity and to provide heating. Such systems are common in countries such as Iceland, Turkey and others. The global operating capacity for geothermal electricity generation from such geothermal resources is about 12.8 GW as of January 2015, spread across 24 countries, and it is expected to reach between 14.5 GW and 17.6 GW by 2020 (Geothermal Energy Association 2015).
There is another type of geothermal energy system, which provides heating and cooling using the ground. That is the type of geothermal energy that is the focus of this book. Such geothermal energy systems take advantage of the energy contained in the ground in its natural state, even when it is not at elevated temperatures due to heat within the earth. This ground energy is related to the background ground temperature and includes the ground itself and groundwater.
1.1 Features of Geothermal Energy
Ground-based energy can be used in all seasons:
Ground-based energy can provide heating directly in winter, since the ground below the surface is often warmer than the air above. Such applications include space heating, greenhouse heating, aquaculture pond heating, agricultural drying, industrial heating uses, bathing and swimming, and snow melting. Sometimes the ground temperature is only adequate to provide preheating. The ground temperature can also be boosted via devices like heat pumps, allowing ground-based energy to provide heating at higher temperatures. The use of geothermal energy via ground-source heat pumps has grown considerably compared to the other applications, primarily due to the technology's ability to achieve high efficiency and to utilize groundwater and/or ground temperature anywhere in the world.
Conversely, ground-based energy can provide direct cooling in summer, since the ground below the surface is often cooler than the hot air above. Again, the ground temperature may only be adequate to provide precooling. But the ground temperature can also be lowered using heat pumps operating in a cooling mode, allowing ground-based energy to provide cooling at lower temperatures.
Although the earth's ultimate geothermal energy potential cannot be estimated based on our current level of knowledge and the unpredictability of technology development, geothermal energy systems of both types are usually classified as renewable energy forms. When such geothermal energy is utilized, the temperature of the ground is returned to its elevated temperature by heat contained within hot regions in the earth, or by the effect of the ambient conditions. Discussions of the renewability of various heat sources vary for the different technologies utilizing the energy source. For example, technologies that utilize the ground at temperatures affected by the ambient conditions can be considered renewable provided the ambient conditions are sustained. The constant heat supply from solar radiation and the sustainability of the hydrological cycle (infiltration and precipitation) guarantees a constant flow of heat to the ground and the renewability of such geothermal sources. The energy replacement often occurs on a time scale comparable with that of the extraction time scale.
Sustainable geothermal energy utilization often refers to how this energy resource is used to meet current energy needs without compromising its future utilization. Estimating the long-term response of geothermal energy sources to current utilization and production capacity levels is important if we are to understand their potential contributions to sustainable development. As a renewable energy source, geothermal energy is often viewed as a contributor to sustainable development and the broader goal of sustainability, provided that they are well designed. Being sustainable goes beyond geothermal energy being a renewable energy form, and includes many of its other characteristics:
Availability.
Geothermal energy in the form of ground at elevated temperature is available in many parts of the world, especially in regions with seismic and volcanic activity. Geothermal energy in the form of ground at ambient temperature is available almost everywhere, although its temperature depends on the location and climate. Geothermal energy is available day and night, every day of the year, and can thus cover base-load energy needs and serve as a supplement to intermittent energy sources. The availability characteristics of intermittent renewable energy forms such as solar and wind are much different.
Compatibility.
Systems exploiting geothermal energy are often compatible with both centralized and distributed energy generation.
Affordability.
Geothermal energy is often exploitable for heating and cooling, and for electricity generation, in an affordable manner. Of course, some geothermal systems are not economically viable, but work is ongoing on several of these to improve commercial prospects.
Acceptability.
Most people are supportive of geothermal energy, in part because it is renewable and often economically viable, and also because geothermal energy systems are not intrusive and usually are invisible. This is not the case for many other renewable energy forms, such as solar and wind.
Barriers to deployment include high capital costs, resource development risks, lack of awareness about geothermal energy, and perceived or real environmental issues.
1.2 Geothermal Energy Systems
Geothermal energy systems can exploit hot reservoirs in the ground, often in the form of natural hot water or steam, to provide heating and electricity generation. The geothermal energy technologies that are used in electricity generation are flash technologies, including double and triple flash units, dry steam, and binary cycles. Electricity generation using flash technologies contribute to nearly 60% of the global market use, with dry steam and binary cycles accounting for 26 and 15% of the global market, respectively (Geothermal Energy Association 2015). Growth in use of such geothermal energy systems for heating and electricity generation is limited by their high capital costs. Geothermal development costs depend on resource temperature and pressure, reservoir depth and permeability, fluid chemistry, location, drilling requirements, size of development, number and type of plants (dry steam, flash, binary or hybrid) used, and whether the project is greenfield or expansion (10–15% less). Development costs are strongly affected by prices of commodities (e.g., oil, steel, and cement). Declines in oil and gas prices can decrease geothermal capital costs.
Geothermal energy systems that provide heating and cooling using the ambient ground are made up of various systems and components. Some of the main systems include ground-source heat pumps, thermal energy storage systems, and district energy (i.e., district heating and/or district cooling) capabilities. They also include many other components, such as compressors, heat exchangers, pumps and pipes. Ground-source heat pump systems are capable of providing heating and cooling in one unit. The capacity of a ground-source heat pump is selected based on the heating and cooling loads, the temperature of the ground, and other parameters. Since most areas do not have balanced heating and cooling loads, the capacity of the heat pump is often selected based on one load. In most regions in the USA, the heat pump capacity matches the cooling load and is oversized for the heating loads. In Europe, ground-source heat pumps are used in the residential sector to cover base heating loads and are integrated with another heating system that covers peak heating loads. The capacity of individual ground-source heat pump units ranges from about 1.5 t for small residential applications to over 40 t for commercial and institutional applications. Technology improvements in ground-source heat pumps are expected to improve the performance and lower the cost of heat pump technologies. Key components such as compressors and heat exchangers will likely provide the largest areas for improvement. The main goals for ground-source heat pumps are reducing capital costs and improving operating efficiency, while expanding the range of products for most of the heating and cooling applications and sub-markets in the building sector.
Thus, geothermal energy systems can provide heating and cooling using the ambient ground, and can exploit hot reservoirs in the ground to provide heating and electricity generation. Both types of geothermal energy are used in practise, and are finding increased application. But the use of geothermal energy systems that use the ground to provide heating and cooling services (the focus of this book) is growing at a particularly noteworthy rate. According to a recent report (Lund and Boyd 2015), the direct use of geothermal energy has experienced an annual growth of 7.7% in capacity over the 5-year period after 2010, with the highest installed thermal capacity in the USA, China, and Sweden. This growth is mainly attributable to the growing popularity of ground-source heat pumps. About 90 000 TJ/year of ground-source heat pump utilization was observed in 2010, and this grew to approximately 325 000 TJ/year by the end of 2014.
Although geothermal energy technologies have been around for over 40 years and are applied in many areas, they are continually undergoing research and development. These efforts allow for system improvements, advances in components and enhanced understanding. Such activity is likely to carry on in the future.
1.3 Outline of the Book
In this book, geothermal energy systems are described that utilize ground energy in conjunction with heat pumps to provide heating and cooling, in a sustainable fashion. Various topics are covered, from thermodynamic fundamentals to advanced discussions on renewability and sustainability. Many applications of such systems are also described, while theory and analysis are emphasized throughout. Detailed descriptions are provided of models for vertical geothermal heat exchangers, and a strong focus is placed on closed-loop geothermal energy systems.
In this chapter, an introduction to geothermal energy as a source of energy and technologies that can harvest it is provided. Some key features of geothermal energy systems, such as its renewability and sustainability, as well as some of its advantages are briefly described. The main components of such systems are reviewed. The aim of this chapter is to provide the reader with basic information to help develop an understanding of the overall scope and range of material that is included in this book.
In Chapter 2, fundamentals of thermodynamics, heat transfer and fluid mechanics that are related to geothermal energy systems are provided to familiarize readers with these topics and prepare them for subsequent chapters. A good knowledge of thermodynamics is important to understanding geothermal energy, especially heat pumps. Facets of thermodynamics most relevant to geothermal energy systems and their applications are introduced and particular attention is paid to the quantity exergy and the methodology derived from it, exergy analysis. Aspects of heat transfer relevant to geothermal energy systems are introduced to provide the reader with a good grounding in heat transfer, which is central to geothermal energy utilization and its application. The three main modes of heat transfer are considered: conduction, convection, and radiation. A good grounding of fluid mechanics helps in understanding geothermal energy systems, as fluid flow problems often arise, so elements of fluid mechanics relevant to geothermal energy systems are also introduced. Finally, basic concepts about the ground are presented, since such material is fundamental to understanding ground-based geothermal systems, including information on ground temperature range and gradients, ground properties, and the existence of ground-based ecosystems and their sensitivity to human activity in the ground.
Chapter 3
