THERMAL ENERGYSTORAGESYSTEMS AND APPLICATIONS,SECOND EDITION

İbrahim DinçerandMarc A. RosenProfessor of Mechanical Engineering

Faculty of Engineering and Applied Science

University of Ontario Institute of Technology

Ontario, Canada

A John Wiley and Sons, Ltd., Publication

ayyappan9780470970737.jpg

THERMAL ENERGYSTORAGE

THERMAL ENERGYSTORAGESYSTEMS AND APPLICATIONS,SECOND EDITION

İbrahim DinçerandMarc A. RosenProfessor of Mechanical Engineering

Faculty of Engineering and Applied Science

University of Ontario Institute of Technology

Ontario, Canada

A John Wiley and Sons, Ltd., Publication

This edition first published 2011Copyright 2011, John Wiley & Sons, Ltd

First Edition published in 2002

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Library of Congress Cataloguing-in-Publication Data

Dincer, Ibrahim, 1964-Thermal energy storage : systems and applications / Ibrahim Dincer, Marc A. Rosen. – 2nd ed.

p. cm.Rev. ed. of: Thermal energy storage systems and applications / [edited by] İbrahim Dincer, and Marc Rosen. c2002.Includes index.ISBN 978-0-470-74706-3 (cloth)

1. Heat storage. I. Rosen, Marc (Marc A.) II. Thermal energy storage systems and applications. III. Title.TJ260.T493 2010621.402′8–dc22

2010020654

A catalogue record for this book is available from the British Library.

Print ISBN: 978-0-470-74706-3ePDF ISBN: 978-0-470-97073-7oBook ISBN: 978-0-470-97075-1

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Front cover image: Borehole thermal energy storage system at the University of Ontario Institute of Technology,Oshawa, Ontario, Canada. The companies involved in the design and construction were Diamond and Schmitt ArchitectsIncorporated and Keen Engineering with Brian Beatty and Associates.

www.wiley.com

To my wife, Gülşen, and my children,Meliha, Miray, İbrahim Eren,

Zeynep, and İbrahim Emirfor their inspiration.

And to those who have helped and supportedme in any way throughout

my education and professional life.İbrahim Dinçer

To my wife, Margot, and my children,Allison and Cassandra for their inspiration.And to Frank C. Hooper and David S. Scott,

two giants in the field of energy and wonderful mentors.Marc A. Rosen

Contents

About the Authors xv

Preface xvii

Acknowledgements xix

1 General Introductory Aspects for Thermal Engineering 11.1 Introduction 11.2 Systems of Units 21.3 Fundamental Properties and Quantities 2

1.3.1 Mass, Time, Length, and Force 21.3.2 Pressure 21.3.3 Temperature 41.3.4 Specific Volume and Density 61.3.5 Mass and Volumetric Flow Rates 6

1.4 General Aspects of Thermodynamics 71.4.1 Thermodynamic Systems 71.4.2 Process 71.4.3 Cycle 71.4.4 Thermodynamic Property 71.4.5 Sensible and Latent Heats 71.4.6 Latent Heat of Fusion 81.4.7 Vapor 81.4.8 Thermodynamic Tables 81.4.9 State and Change of State 91.4.10 Specific Internal Energy 101.4.11 Specific Enthalpy 101.4.12 Specific Entropy 111.4.13 Pure Substance 111.4.14 Ideal Gases 111.4.15 Energy Transfer 151.4.16 Heat 161.4.17 Work 161.4.18 The First Law of Thermodynamics 171.4.19 The Second Law of Thermodynamics 171.4.20 Reversibility and Irreversibility 181.4.21 Exergy 18

1.5 General Aspects of Fluid Flow 201.5.1 Classification of Fluid Flows 201.5.2 Viscosity 22

viii Contents

1.5.3 Equations of Flow 231.5.4 Boundary Layer 29

1.6 General Aspects of Heat Transfer 321.6.1 Conduction Heat Transfer 331.6.2 Convection Heat Transfer 341.6.3 Radiation Heat Transfer 361.6.4 Thermal Resistance 371.6.5 The Composite Wall 381.6.6 The Cylinder 381.6.7 The Sphere 391.6.8 Conduction with Heat Generation 401.6.9 Natural Convection 421.6.10 Forced Convection 43

1.7 Concluding Remarks 45

2 Energy Storage Systems 512.1 Introduction 512.2 Energy Demand 522.3 Energy Storage 532.4 Energy Storage Methods 54

2.4.1 Mechanical Energy Storage 542.4.2 Chemical Energy Storage 622.4.3 Biological Storage 752.4.4 Magnetic Storage 752.4.5 Thermal Energy Storage (TES) 76

2.5 Hydrogen for Energy Storage 772.5.1 Storage Characteristics of Hydrogen 772.5.2 Hydrogen Storage Technologies 772.5.3 Hydrogen Production 78

2.6 Comparison of ES Technologies 802.7 Concluding Remarks 80

3 Thermal Energy Storage (TES) Methods 833.1 Introduction 833.2 Thermal Energy 843.3 Thermal Energy Storage 85

3.3.1 Basic Principle of TES 863.3.2 Benefits of TES 893.3.3 Criteria for TES Evaluation 903.3.4 TES Market Considerations 963.3.5 TES Heating and Cooling Applications 993.3.6 TES Operating Characteristics 1033.3.7 ASHRAE TES Standards 104

3.4 Solar Energy and TES 1043.4.1 TES Challenges for Solar Applications 1053.4.2 TES Types and Solar Energy Systems 1053.4.3 Storage Durations and Solar Applications 1063.4.4 Building Applications of TES and Solar Energy 1073.4.5 Design Considerations for Solar Energy-Based TES 108

3.5 TES Methods 1093.6 Sensible TES 109

3.6.1 Thermally Stratified TES Tanks 111

Contents ix

3.6.2 Concrete TES 1143.6.3 Rock and Water/Rock TES 1143.6.4 Aquifer Thermal Energy Storage (ATES) 1183.6.5 Solar Ponds 1243.6.6 Evacuated Solar Collector TES 125

3.7 Latent TES 1273.7.1 Operational Aspects of Latent TES 1283.7.2 Phase Change Materials (PCMs) 129

3.8 Cold Thermal Energy Storage (CTES) 1423.8.1 Working Principle 1423.8.2 Operational Loading of CTES 1433.8.3 Design Considerations 1443.8.4 CTES Sizing Strategies 1463.8.5 Load Control and Monitoring in CTES 1473.8.6 CTES Storage Media Selection and Characteristics 1483.8.7 Storage Tank Types for CTES 1523.8.8 Chilled-Water CTES 1533.8.9 Ice CTES 1583.8.10 Ice Forming 1743.8.11 Ice Thickness Controls 1743.8.12 Technical and Design Aspects of CTES 1783.8.13 Selection Aspects of CTES 1793.8.14 Cold-Air Distribution in CTES 1803.8.15 Potential Benefits of CTES 1833.8.16 Electric Utilities and CTES 184

3.9 Seasonal TES 1853.9.1 Seasonal TES for Heating Capacity 1853.9.2 Seasonal TES for Cooling Capacity 1863.9.3 Illustration 186

3.10 Concluding Remarks 187

4 Thermal Energy Storage and Environmental Impact 1914.1 Introduction 1914.2 Energy and the Environment 1924.3 Major Environmental Problems 193

4.3.1 Acid Rain 1944.3.2 Greenhouse Effect (Global Climate Change) 1954.3.3 Stratospheric Ozone Depletion 196

4.4 Environmental Impact and TES Systems and Applications 1984.5 Potential Solutions to Environmental Problems 198

4.5.1 General Solutions 1984.5.2 TES-Related Solutions 199

4.6 Sustainable Development 1994.6.1 Conceptual Issues 2004.6.2 The Brundtland Commission’s Definition 2004.6.3 Environmental Limits 2014.6.4 Global, Regional, and Local Sustainability 2014.6.5 Environmental, Social, and Economic Components of Sustainability 2014.6.6 Energy and Sustainable Development 2024.6.7 Environment and Sustainable Development 2024.6.8 Achieving Sustainable Development in Larger Countries 2034.6.9 Essential Factors for Sustainable Development 203

x Contents

4.7 Illustrative Examples and Case Studies 2044.7.1 The South Coast Air Quality Management District (California) 2044.7.2 Anova Verzekering Co. Building (Amersfoort, The Netherlands) 2044.7.3 The Trane Company’s Technology Center (La Crosse, WI) 2054.7.4 The Ministry of Finance Building (Bercy, France) 2064.7.5 The City of Saarbrucken (Saarbrucken, Germany) 207

4.8 Concluding Remarks 207

5 Thermal Energy Storage and Energy Savings 2115.1 Introduction 2115.2 TES and Energy Savings 212

5.2.1 Utilization of Waste or Surplus Energy 2135.2.2 Reduction of Demand Charges 2145.2.3 Deferring Equipment Purchases 215

5.3 Additional Energy Savings Considerations for TES 2155.3.1 Energy for Heating, Refrigeration, and Heat Pump Equipment 2155.3.2 Storage Size Limitations 2165.3.3 Thermal Load Profiles 2165.3.4 Optimization of Conventional Systems 217

5.4 Energy Conservation with TES: Planning and Implementation 2175.5 Some Limitations on Increased Efficiency 218

5.5.1 Practical and Theoretical Limitations 2185.5.2 Efficiency Limitations and Exergy 219

5.6 Energy Savings for Cold TES 2195.6.1 Economic Aspects of TES Systems for Cooling Capacity 2215.6.2 Energy Savings by Cold TES 2215.6.3 Case Studies for TES Energy Savings 225

5.7 Concluding Remarks 230

6 Energy and Exergy Analyses of Thermal Energy Storage Systems 2336.1 Introduction 2336.2 Theory: Energy and Exergy Analyses 234

6.2.1 Motivation for Energy and Exergy Analyses 2356.2.2 Conceptual Balance Equations for Mass, Energy, and Entropy 2356.2.3 Detailed Balance Equations for Mass, Energy, and Entropy 2366.2.4 Basic Quantities for Exergy Analysis 2386.2.5 Detailed Exergy Balance 2406.2.6 The Reference Environment 2416.2.7 Efficiencies 2436.2.8 Properties for Energy and Exergy Analyses 2446.2.9 Implications of Results of Exergy Analyses 2456.2.10 Steps for Energy and Exergy Analyses 246

6.3 Thermodynamic Considerations in TES Evaluation 2466.3.1 Determining Important Analysis Quantities 2466.3.2 Obtaining Appropriate Measures of Efficiency 2466.3.3 Pinpointing Losses 2476.3.4 Assessing the Effects of Stratification 2486.3.5 Accounting for Time Duration of Storage 2486.3.6 Accounting for Variations in Reference-Environment Temperature 2496.3.7 Closure 249

Contents xi

6.4 Exergy Evaluation of a Closed TES System 2496.4.1 Description of the Case Considered 2506.4.2 Analysis of the Overall Process 2516.4.3 Analysis of Subprocesses 2536.4.4 Alternative Formulations of Subprocess Efficiencies 2556.4.5 Relations between Performance of Subprocesses and Overall Process 2566.4.6 Example 2576.4.7 Closure 260

6.5 Appropriate Efficiency Measures for Closed TES Systems 2606.5.1 TES Model Considered 2616.5.2 Energy and Exergy Balances 2616.5.3 Energy and Exergy Efficiencies 2626.5.4 Overall Efficiencies 2626.5.5 Charging-Period Efficiencies 2636.5.6 Storing-Period Efficiencies 2636.5.7 Discharging-Period Efficiencies 2646.5.8 Summary of Efficiency Definitions 2656.5.9 Illustrative Example 2666.5.10 Closure 267

6.6 Importance of Temperature in Performance Evaluations for Sensible TES Systems 2696.6.1 Energy, Entropy, and Exergy Balances for the TES System 2696.6.2 TES System Model Considered 2696.6.3 Analysis 2706.6.4 Comparison of Energy and Exergy Efficiencies 2716.6.5 Illustration 2726.6.6 Closure 272

6.7 Exergy Analysis of Aquifer TES Systems 2726.7.1 ATES Model 2736.7.2 Energy and Exergy Analyses 2746.7.3 Effect of a Threshold Temperature 2776.7.4 Case Study 2776.7.5 Closure 281

6.8 Exergy Analysis of Thermally Stratified Storages 2816.8.1 General Stratified TES Energy and Exergy Expressions 2826.8.2 Temperature-Distribution Models and Relevant Expressions 2846.8.3 Discussion and Comparison of Models 2896.8.4 Illustrative Example: The Exergy-Based Advantage of Stratification 2896.8.5 Illustrative Example: Evaluating Stratified TES Energy and Exergy 2906.8.6 Increasing TES Exergy-Storage Capacity Using Stratification 2936.8.7 Illustrative Example: Increasing TES Exergy with Stratification 2976.8.8 Closure 297

6.9 Energy and Exergy Analyses of Cold TES Systems 2986.9.1 Energy Balances 2996.9.2 Exergy Balances 3016.9.3 Energy and Exergy Efficiencies 3016.9.4 Illustrative Example 3026.9.5 Case Study: Thermodynamic Performance of a Commercial Ice TES System 3046.9.6 Closure 309

6.10 Exergy-Based Optimal Discharge Periods for Closed TES Systems 3096.10.1 Analysis Description and Assumptions 309

xii Contents

6.10.2 Evaluation of Storage-Fluid Temperature During Discharge 3106.10.3 Discharge Efficiencies 3116.10.4 Exergy-Based Optimum Discharge Period 3126.10.5 Illustrative Example 3126.10.6 Closure 314

6.11 Exergy Analysis of Solar Ponds 3146.11.1 Experimental Solar Pond 3156.11.2 Data Acquisition and Analysis 3166.11.3 Energy and Exergy Assessments 3206.11.4 Potential Improvements 322

6.12 Concluding Remarks 323Appendix: Glossary of Selected Exergy-Related Terminology 332

7 Numerical Modeling and Simulation of Thermal Energy Storage Systems 3357.1 Introduction 3357.2 Approaches and Methods 3367.3 Selected Applications 3377.4 Numerical Modeling, Simulation, and Analysis of Sensible TES Systems 340

7.4.1 Modeling 3407.4.2 Heat Transfer and Fluid Flow Analysis 3437.4.3 Simulation 3447.4.4 Thermodynamic Analysis 347

7.5 Case Studies for Sensible TES Systems 3497.5.1 Case Study 1: Natural Convection in a Hot Water Storage Tank 3497.5.2 Case Study 2: Forced Convection in a Stratified Hot Water Tank 3557.5.3 General Discussion of Sensible TES Case Studies 365

7.6 Numerical Modeling, Simulation, and Analysis of Latent TES Systems 3667.6.1 Modeling 3667.6.2 Heat Transfer and Fluid Flow Analysis 3667.6.3 Simulation 3687.6.4 Thermodynamic Analysis 368

7.7 Case Studies for Latent TES Systems 3697.7.1 Case Study 1: Two-Dimensional Study of the Melting Process in an Infinite

Cylindrical Tube 3697.7.2 Case Study 2: Melting and Solidification of Paraffin in a Spherical Shell

from Forced External Convection 3767.8 Illustrative Application for a Complex System: Numerical Assessment of Encapsulated

Ice TES with Variable Heat Transfer Coefficients 3917.8.1 Background 3917.8.2 System Considered 3927.8.3 Modeling and Simulation 3927.8.4 Numerical Determination of Heat Transfer Coefficients for Spherical

Capsules 3977.8.5 Heat Transfer Coefficients and Correlations 3987.8.6 Closing Remarks for Illustrative Application for a Complex System 404

7.9 Concluding Remarks 406

8 Thermal Energy Storage Case Studies 4138.1 Introduction 4138.2 Ice CTES Case Studies 414

8.2.1 Rohm and Haas, Spring House Research Facility, PA 4148.2.2 A Cogeneration Facility, California 416

Contents xiii

8.2.3 A Power Generation Plant, Gaseem, Saudi Arabia 4218.2.4 Channel Island Power Station, Darwin, Australia 4278.2.5 The Abraj Atta’awuneya Ice CTES Project, Riyadh, Saudi Arabia 4298.2.6 Alitalia’s Headquarters Building, Rome, Italy 431

8.3 Ice-Slurry CTES Case Studies 4328.3.1 The Stuart C. Siegel Center at Virginia Commonwealth University, VA 4328.3.2 A Slurry Ice Rapid Cooling System, Boston, UK 435

8.4 Chilled Water CTES Case Studies 4368.4.1 The Central Chilled Water System at the University of North Carolina, NC 4368.4.2 Chilled Water CTES in a Trigeneration Project for a World Fair (EXPO’98),

Lisbon, Portugal 4388.4.3 TES at a Federal Facility, TX 444

8.5 PCM-Based CTES Case Studies 4468.5.1 Minato Mirai 21, Yokohama 4468.5.2 Harp Brewery, Dundalk, Ireland 4478.5.3 Korean Development Bank, Seoul 4498.5.4 Museum of Sciences and Industry, La Villette, France 4508.5.5 Rueil Malmaison Central Kitchen, France 4518.5.6 The Bangsar District Cooling Plant, Malaysia 4538.5.7 Dairy TES Application Using Eutectic Solutions, Dorset, UK 454

8.6 PCM-Based Latent TES for Heating Case Studies 4558.6.1 Solar Power Tower in Sandia National Laboratories, NM 455

8.7 Sensible TES Case Studies 4578.7.1 New TES in Kumamuto, Kyushu 4578.7.2 The World’s First Passive Annual Heat Storage Home, MT 458

8.8 Other Case Studies 4598.8.1 Potential for TES in a Hotel in Bali 4598.8.2 Integrated TES Community System: Drake Landing Solar Community 4648.8.3 The Borehole TES System at the University of Ontario Institute

of Technology 4718.9 Concluding Remarks 479

9 Recent Advances in TES Methods, Technologies, and Applications 4839.1 Introduction 4839.2 Recent TES Investigations 4839.3 Developments in TES Types and Performance 486

9.3.1 Developments in PCM/HTF Material Selection 4869.3.2 Shape 4919.3.3 Nano- to Macro-Size Storage Media or PCM Particles and Capsules 4939.3.4 Recent Advances in TES Types and Storage Techniques 497

9.4 Micro- and Macro-Level Advances in TES Systems and Applications 5049.5 Micro-Level Advances in TES Systems 504

9.5.1 Modeling Methods 5049.5.2 Contact Melting Driven by Temperature and Pressure Differences 5059.5.3 Supercooling, Superheating, and Hysteresis 5099.5.4 Geometry and Performance Optimization 5129.5.5 Other Micro-Level Phenomena Affecting TES Performance 5129.5.6 Developments in Stratification Analysis 513

9.6 Macro-Level Advances in TES Systems and Applications 5149.6.1 Mode of Cooling/Heating: Passive or Active 5149.6.2 Operating Strategies and Installation Configurations 5209.6.3 Modeling, Control, Programming, and Optimization Methods 524

xiv Contents

9.6.4 Measurement and Visualization Methods 5279.6.5 Auxiliaries 529

9.7 Performance Enhancement Techniques 5309.7.1 Conductivity-Enhancing Techniques 5309.7.2 Thermal Batteries 5309.7.3 Other Techniques 534

9.8 Innovative Applications of TES Systems 5359.9 Advanced Applications of Exergy Methods 5429.10 Illustrative Examples 545

9.10.1 Use of Effectiveness to Complement TES Energy and Exergy Efficiencies 5459.10.2 Thermal Battery Ice-Storage System 5549.10.3 Use of Artificial Neural Networks in TES 560

9.11 Future Outlook for TES 566

Appendix A Conversion Factors 585

Appendix B Thermophysical Properties 587

Appendix C Glossary 593

Index 595

About the Authorsİbrahim Dinçer is a full professor of mechanical engineering in the Faculty of Engineering andApplied Science at University of Ontario Institute of Technology (UOIT). Renowned for his pio-neering works in the area of sustainable energy technologies, he has authored and co-authorednumerous books and book chapters, more than 600 refereed journal and conference papers, andmany technical reports. He has chaired many national and international conferences, symposia,workshops, and technical meetings. He has delivered more than 200 keynote and invited lectures.He is an active member of various international scientific organizations and societies, and serves aseditor-in-chief (for International Journal of Energy Research by Wiley, and International Journalof Exergy and International Journal of Global Warming by Inderscience), associate editor, regionaleditor, and editorial board member on various prestigious international journals. He is a recipientof several research, teaching, and service awards, including a Premier’s Research Excellence awardin Ontario, Canada, in 2004. He has made innovative contributions to the understanding and devel-opment of sustainable energy technologies and their implementation, particularly through exergy.He has actively been working in the areas of hydrogen and fuel cell technologies, and his grouphas developed various novel technologies and methods.

Marc A. Rosen is a professor of mechanical engineering at the University of Ontario Institute ofTechnology in Oshawa, Canada, where he served as founding Dean of the Faculty of Engineeringand Applied Science from 2002 to 2008. Dr. Rosen has served as President of the EngineeringInstitute of Canada and of the Canadian Society for Mechanical Engineering. He has acted in manyprofessional capacities, including founding editor-in-chief of the journal Sustainability and a mem-ber of the Board of Directors of Oshawa Power and Utilities Corporation. With over 60 researchgrants and contracts and 500 technical publications, Dr. Rosen is an active teacher and researcherin thermodynamics, energy technology, sustainable energy, and the environmental impact of energysystems. Much of his research has been carried out for industry. Dr. Rosen has worked for suchorganizations as Imatra Power Company in Finland, Argonne National Laboratory near Chicago,the Institute for Hydrogen Systems near Toronto, and Ryerson University in Toronto, where heserved as chair of the Department of Mechanical, Aerospace and Industrial Engineering. Dr. Rosenhas received numerous awards and honours, including an Award of Excellence in Research andTechnology Development from the Ontario Ministry of Environment and Energy, the Engineer-ing Institute of Canada’s Smith Medal for achievement in the development of Canada, and theCanadian Society for Mechanical Engineering’s Angus Medal for outstanding contributions to themanagement and practice of mechanical engineering. He is a Fellow of the Engineering Institute ofCanada, the Canadian Academy of Engineering, the Canadian Society for Mechanical Engineering,the American Society of Mechanical Engineers, and the International Energy Foundation.

PrefaceThermal energy storage (TES) is an advanced energy technology that is attracting increasing interestfor thermal applications such as space and water heating, cooling, and air conditioning. TES systemshave enormous potential to facilitate more effective use of thermal equipment and large-scale energysubstitutions that are economic. TES appears to be the most appropriate method for correcting themismatch that sometimes occurs between the supply and demand of energy. It is therefore a veryattractive technology for meeting society’s needs and desires for more efficient and environmentallybenign energy use.

This book is research oriented, and therefore includes some practical features often not included inother, solely academic textbooks. This book is essentially intended for use by advanced undergrad-uate and graduate students in various disciplines ranging from mechanical to chemical engineering,and as a basic reference for practicing energy engineers. Analyses of TES systems and theirapplications are undertaken throughout this comprehensive book, providing new understanding,methodologies, models, and applications, along with descriptions of several experimental worksand case studies. Some of the material presented has been drawn from recent information availablein the literature and elsewhere. The coverage is extensive, and the amount of information and datapresented can be sufficient for several courses, if studied in detail. We strongly believe that thisbook will be of interest to students, engineers, and energy experts and that it provides a valuableand readable reference text for those who wish to learn more about TES systems and applications.

Chapter 1 addresses general aspects of thermodynamics, fluid flow, and heat transfer to furnishthe reader with background information that is of relevance to the analysis of TES systems andtheir applications. Chapter 2 discusses the many types of energy storage technologies available.Chapter 3 deals extensively with TES methods, including cold TES. Chapter 4 addresses severalenvironmental issues that we face today, and discusses how TES can help solve these problems.Several successful case studies are presented. Chapter 5 describes how TES is a valuable toolin energy conservation efforts that can help achieve significant energy savings. Chapter 6 coversenergy and exergy analyses of a range of TES systems, along with various practical examples.Chapter 7 delves into both sensible and latent TES systems and their modeling, simulation, andnumerical analyses; numerous case studies and illustrative examples are incorporated into thischapter, including heat transfer with phase change in simple and complex geometries. Chapter 8discusses many practical TES applications and case studies along with their technical features andpotential benefits. As the final unit, Chapter 9 reflects current developments in TES systems andapplications, technologies, methods and techniques, and thereby seeks to provide thoughts on thefuture of thermal energy storage.

Incorporated throughout this book are many wide-ranging, illustrative examples that provideuseful information for practical applications. Conversion factors and thermophysical properties ofvarious materials are listed in the appendices in the International System of Units (SI). Completereferences and a bibliography are included with each chapter to direct the curious and interestedreader to further information.

xviii Preface

The second edition of this book includes updated materials, new chapters, and questions/problemsfor each chapter. We feel that the enhanced content makes this edition of Thermal Energy Storage:Systems and Applications the best candidate as a text for senior level undergraduate and/or graduatelevel courses in the area.

İbrahim DinçerMarc A. Rosen

August 2010

AcknowledgementsMany people and organizations provided assistance that helped greatly in bringing this edition ofour book to fruition.

We are most grateful to the following colleagues, postdoctoral fellows, and graduate students ofours for the time and effort they dedicated to assist in the preparation of some chapters, sections,figures, and problems:

• Mr. Hooman Abdi• Mr. Mustafa Tolga Balta• Dr. Aytunc Erek• Mr. Othman Jaber• Dr. Mehmet Karakilcik• Mr. David MacPhee• Mr. Bayu Susila

Their assistance helped us enhance the content and make it more focused as a comprehensiveresource and textbook on thermal energy storage.

We are particularly thankful to the many companies and agencies that contributed documents andillustrations for use in this book. These valuable materials permit us to cover many recent devel-opments and to provide a high degree of industrial relevance and practicality. Most such materialsfrom the first edition are retained in this edition, because of their continuing illustrative nature andrelevance. Furthermore, new materials from industry are included in this edition to enhance the cov-erage of practical applications. The relevant companies and agencies are acknowledged throughoutthe book where elements of the materials they provided are utilized.

We are grateful to several reviewers, colleagues, friends, and graduate students of ours for thefeedback and suggestions they provided during the preparation of the first and current editions ofthis book.

We acknowledge the support provided by our former and current academic institutions.In this second edition, several externally contributed chapters from the first edition have been

replaced in order to provide a more unified and cohesive presentation. We nonetheless acknowledgewith sincere thanks the chapters that were contributed to the first edition by Professors Adrian Bejan,Afshin J. Ghajar, Kamal A.R. Ismail, Marcel Lacroix, and Yousef H. Zurigat.

Also, we sincerely appreciate the encouragement of our publisher and their recognition of theincreasing importance of thermal energy storage. In addition, we are grateful for the exemplarysupport provided by Nicky Skinner and Debbie Cox of John Wiley & Sons in the development ofthis second edition of the book, from the initial review phase to the final product.

Last, but not least, we thank our wives, Gülşen Dinçer and Margot Rosen, and our childrenMeliha, Miray, İbrahim Eren, Zeynep, and İbrahim Emir Dinçer, and Allison and Cassandra Rosen.They have been a great source of support and motivation, and their patience and understandingthroughout this project have been most appreciated.

1General Introductory Aspectsfor Thermal Engineering

1.1 IntroductionThermal energy storage (TES) is one of the key technologies for energy conservation, and therefore,it is of great practical importance. One of its main advantages is that it is best suited for heatingand cooling thermal applications. TES is perhaps as old as civilization itself. Since recorded time,people have harvested ice and stored it for later use. Large TES systems have been employed inmore recent history for numerous applications, ranging from solar hot water storage to building airconditioning systems. The TES technology has only recently been developed to a point where itcan have a significant impact on modern technology.

In general, a coordinated set of actions has to be taken in several sectors of the energy system forthe maximum potential benefits of thermal storage to be realized. TES appears to be an importantsolution to correcting the mismatch between the supply and demand of energy. TES can contributesignificantly to meeting society’s needs for more efficient, environmentally benign energy use. TESis a key component of many successful thermal systems, and a good TES should allow little thermallosses, leading to energy savings, while permitting the highest reasonable extraction efficiency ofthe stored thermal energy.

There are mainly two types of TES systems, that is, sensible (e.g., water and rock) and latent(e.g., water/ice and salt hydrates). For each storage medium, there is a wide variety of choicesdepending on the temperature range and application. TES via latent heat has received a great dealof interest. Perhaps, the most obvious example of latent TES is the conversion of water to ice.Cooling systems incorporating ice storage have a distinct size advantage over equivalent capacitychilled water units because of the ability to store large amount of energy as latent heat. TESdeals with the storing of energy, usually by cooling, heating, melting, solidifying, or vaporizing asubstance, and the energy becomes available as heat when the process is reversed. The selection ofa TES is mainly dependent on the storage period required, that is, diurnal or seasonal, economicviability, operating conditions, and so on. In practice, many research and development activitiesrelated to energy have concentrated on efficient energy use and energy savings, leading to energyconservation. In this regard, TES appears to be an attractive thermal application. Furthermore,exergy analysis is an important tool for analyzing TES performance.

We begin this chapter with a summary of fundamental definitions, physical quantities, and theirunits, dimensions, and interrelations. We consider introductory aspects of thermodynamics, fluidflow, heat transfer, energy, entropy, and exergy.

Thermal Energy Storage: Systems and Applications, Second Edition İbrahim Dinçer and Marc A. Rosen 2011 John Wiley & Sons, Ltd

2 Thermal Energy Storage

1.2 Systems of UnitsThere are two main systems of units: the International System of Units (Le Systéme Internationald’Unités), which is normally referred to as SI units , and the English System of Units . SI units areused most widely throughout the world, although the English System is traditional in the UnitedStates. In this book, SI units are primarily employed. Note that the relevant unit conversions andrelationships between the International and English unit systems concerning fundamental propertiesand quantities are listed in Appendix A.

1.3 Fundamental Properties and QuantitiesIn this section, we briefly cover several general aspects of thermodynamics to provide adequatepreparation for the study of TES systems and applications.

1.3.1 Mass, Time, Length, and Force

Mass is defined as a quantity of matter forming a body of indefinite shape and size. The fundamentalunit of mass is the kilogram (kg) in SI units and the pound mass (lbm) in English units. The basicunit of time for both unit systems is the second.

In thermodynamics, the unit mole (mol) is commonly used and defined as a certain amount ofa substance as follows:

n = mM

(1.1)

where n is the number of moles, m is the mass, and M is the molecular weight. If m and M aregiven in units of gram and gram per mole, we obtain n in moles. For example, one mole of water,having a molecular weight of 18 (compared to 12 for carbon-12), has a mass of 0.018 kg.

The basic unit of length is the meter (m) in SI units and the foot (ft) in the English system.A force is a kind of action that brings a body to rest or changes its speed or direction of motion

(e.g., a push or a pull). The fundamental unit of force is the Newton (N).The four aspects, for example, mass, time, length, and force, are related by the Newton’s second

law of motion, which states that the force acting on a body is proportional to the mass and theacceleration in the direction of the force, as given in Equation 1.2:

F = ma (1.2)Equation 1.2 shows the force required to accelerate a mass of one kilogram at a rate of one meterper second per second as 1 N = 1 kg m/s2.

It is important to note that the value of the earth’s gravitational acceleration is 9.80665 m/s2 inthe SI system and 32.174 ft/s2 in the English system, and it indicates that a body falling freelytoward the surface of the earth is subject to the action of gravity alone.

1.3.2 Pressure

When we deal with liquids and gases, pressure becomes one of the most important quantities.Pressure is the force exerted on a surface, per unit area, and is expressed in bar or Pascal (Pa). Therelated expression is

P = FA

(1.3)

General Introductory Aspects for Thermal Engineering 3

Pre

ssur

e

Pressure gauge ∆P = Pabs,p – Patm

Atmospheric pressure

Vacuum gauge ∆P = Patm – Pabs,n

Pabs,n

Patm

Pabs,p

0

Figure 1.1 Illustration of pressures for measurement

The SI unit for pressure is the force of one Newton acting on a square meter area (or the Pascal ).The unit for pressure in the English system is pound-force per square foot, lbf/ft2.

Here, we introduce basic pressure definitions, and a summary of basic pressure measurementrelationships is shown in Figure 1.1.

Atmospheric Pressure The atmosphere that surrounds the earth can be considered a reservoir oflow-pressure air. Its weight exerts a pressure which varies with temperature, humidity, and altitude.Atmospheric pressure also varies from time to time at a single location because of the movementof weather patterns. While these changes in barometric pressure are usually less than one-half inchof mercury, they need to be taken into account when precise measurements are required.

Gauge Pressure The gauge pressure is any pressure for which the base for measurement isatmospheric pressure expressed as kPa (gauge). Atmospheric pressure serves as a reference levelfor other types of pressure measurements, for example, gauge pressure. As shown in Figure 1.1,the gauge pressure is either positive or negative depending on its level above or below atmosphericlevel. At the level of atmospheric pressure, the gauge pressure becomes zero.

Absolute Pressure A different reference level is utilized to obtain a value for absolute pressure.The absolute pressure can be any pressure for which the base for measurement is a completevacuum, and is expressed in kPa (absolute). Absolute pressure is composed of the sum of thegauge pressure (positive or negative) and the atmospheric pressure as follows:

pressure (gauge) + atmospheric pressure = pressure (absolute) (1.4)For example, to obtain the absolute pressure, we simply add the value of atmospheric pressure to

gauge pressure. The absolute pressure is the most common one used in thermodynamic calculations,despite the fact that what is read by most pressure gauges and indicators is the pressure differencebetween the absolute pressure and the atmospheric pressure existing in the gauge.

Vacuum A vacuum is a pressure lower than atmospheric pressure and occurs only in closedsystems, except in outer space. It is also called negative gauge pressure. In fact, a vacuum is thepressure differential produced by evacuating air from the closed system. A vacuum is usually dividedinto four levels: (i) low vacuum representing pressures above 1 Torr absolute (a large number of

4 Thermal Energy Storage

mechanical pumps in industries are used for this purpose; flow is viscous), (ii) medium vacuumvarying between 1 and 10−3 Torr absolute (most pumps serving this range are mechanical; fluidis in transition between viscous and molecular phases), (iii) high vacuum ranging between 10−3and 10−6 Torr absolute (nonmechanical ejector or cryogenic pumps are used; flow is molecular orNewtonian), and (iv) very high vacuum representing absolute pressure below 10−6 Torr (primarilyfor laboratory applications and space simulation).

It is important to note an additional term, the saturation pressure, which is the pressure of aliquid or vapor at saturation conditions.

1.3.3 Temperature

Temperature is an indication of the thermal energy stored in a substance. In other words, we canidentify hotness and coldness with the concept of temperature. The temperature of a substancemay be expressed in either relative or absolute units. The two most common temperature scalesare Celsius (◦C) and Fahrenheit (◦F). The Celsius scale is used with the SI unit system and theFahrenheit scale with the English system of units. There are two additional scales, the Kelvin scale(K) and the Rankine scale (R), which are absolute temperature scales and are often employed inthermodynamic applications.

The degree Kelvin is a unit of temperature measurement; zero kelvin (0 K) is absolute zero andis equal to −273.15 ◦C. Increments of temperature in units of K and ◦C are equal. For instance,when the temperature of a product is decreased to −273.15 ◦C (or 0 K), known as absolute zero,the substance contains no thermal energy and all molecular movement stops.

Temperature can be measured in a large number of ways by devices. In general, the followingdevices are commonly used:

• Thermometers. Thermometers contain a volume of fluid which expands when subjected toheat, thereby raising its temperature. In practice, thermometers work over a certain temperaturerange. For example, the common thermometer fluid, mercury, becomes solid at −38.8 ◦C and itsproperties change dramatically at that condition.

• Resistance thermometers. A resistance thermometer (or detector), also known as a wire-woundthermometer, has great accuracy for wide temperature ranges. The wire used has to have known,repeatable, electrical characteristics so that the relationship between the temperature and resis-tance value can be predicted precisely. The measured value of the resistance of the detector canthen be used to determine the value of an unknown temperature. Among metallic conductors,pure metals exhibit the greatest change of resistance with temperature. For applications requiringhigher accuracy, especially where the temperature measurement is between −200 and +800 ◦C,the resistance thermometer comes into its own. The majority of such thermometers are made ofplatinum. In industries, in addition to platinum, nickel (−60 to +180 ◦C) and copper (−30 to+220 ◦C) are frequently used to manufacture resistance thermometers. Resistance thermometerscan be provided with two, three, or four wire connections, and for higher accuracy at least threewires are required.

• Averaging thermometers. An averaging thermometer is designed to measure the average tem-perature of bulk stored liquids. The sheath contains a number of elements of different lengths,all starting from the bottom of the sheath, The longest element that is fully immersed is con-nected to the measuring circuit to allow a true average temperature to be obtained. For thistype of thermometer, several parameters are significant, namely, sheath material (stainless steelfor the temperature range from −50 to +200 ◦C or nylon for the temperature range from −50to +90 ◦C), sheath length (to suit the application), termination (flying leads or terminal box),element length, element calibration (to copper or platinum curves), and operating temperature

General Introductory Aspects for Thermal Engineering 5

ranges. In many applications, where a multielement thermometer is not required, such as in airducts, cooling water and gas outlets, a single-element thermometer stretched across the duct orpipe work can provide a true average temperature reading. Despite the working range from 0 to100 ◦C, the maximum temperature may reach 200 ◦C. To maintain high accuracy, these units arenormally supplied with three-wire connections. However, up to 10 elements can be mounted inthe averaging bulb fittings, and they can be made of platinum, nickel, or copper, and fixed atany required position.

• Thermocouples. A thermocouple consists of two electrical conductors of different materialsconnected together at one end (the so-called measuring junction). The two free ends are con-nected to a measuring instrument, for example, an indicator, a controller, or a signal conditioner,by a reference junction (the so-called cold junction). The thermoelectric voltage appearing atthe indicator depends on the materials of which the thermocouple wires are made and on thetemperature difference between the measuring junction and the reference junction. For accuratemeasurements, the temperature of the reference junction must be kept constant. Modern instru-ments usually incorporate a cold junction reference circuit and are supplied ready for operationin a protective sheath, to prevent damage to the thermocouple by any mechanical or chemi-cal means. Table 1.1 lists several types of thermocouples along with their maximum absolutetemperature ranges. As can be seen in Table 1.1, a copper–constantan thermocouple has anaccuracy of ±1 ◦C, and is often employed for control systems in refrigeration and food pro-cessing applications. The iron–constantan thermocouple with its maximum of 850 ◦C is used inapplications in the plastics industry. The chromel–alumel-type thermocouples, with a maximumof about 1100 ◦C, are suitable for combustion applications in ovens and furnaces. In addition,it is possible to reach about 1600 or 1700 ◦C using platinum rhodium–platinum thermocouples,which are particularly useful in steel manufacturing. It is worth noting that one advantage that thethermocouple has over most other temperature sensors is that it has a small thermal capacity, andthus a prompt response to temperature changes. Furthermore, its small thermal capacity rarelyaffects the temperature of the body under examination.

• Thermistors. These devices are made of semiconductors and act as thermal resistors with a high(usually negative) temperature coefficient. In use, thermistors are either self-heated or externallyheated. Self-heated units employ the heating effect of the current flowing through them to raiseand control their temperature and thus their resistance. This operating mode is useful in suchdevices as voltage regulators, microwave power meters, gas analyzers, flow meters, and automaticvolume and power level controls. Externally heated thermistors are well suited for precisiontemperature measurement, temperature control, and temperature compensation due to the largechanges in resistance versus temperature. These are generally used for applications in the range

Table 1.1 Some of the most common thermocouples

Type Common names Temperature range (◦C)

T Copper–constantan (C/C) −250 to 400J Iron–constantan (I/C) −200 to 850E Nickel chromium–constantan or Chromel–constantan −200 to 850K Nickel chromium–nickel aluminum or Chromel–alumel (C/A) −180 to 1100– Nickel 18% molybdenum–nickel 0 to 1300

N Nicrosil–nisil 0 to 1300S Platinum 10% rhodium–platinum 0 to 1500R Platinum 13% rhodium–platinum 0 to 1500B Platinum 30% rhodium–platinum 6% rhodium 0 to 1600

6 Thermal Energy Storage

−100 to +300 ◦C. Despite early thermistors having tolerances of ±20 or ±10%, modern precisionthermistors are of a higher accuracy, for example, ±0.1 ◦C (less than ±1%).

• Digital display thermometers. A wide range of digital display thermometers, for example,hand-held battery-powered displays and panel-mounted mains or battery units, are availablecommercially. Displays can be provided for use with all standard thermocouples or platinumresistance thermometers with several digits and 0.1 ◦C resolution.

It is important to emphasize that before temperature can be controlled, it must be sensed andmeasured accurately. For temperature measurement devices, there are several potential sources oferror, including not only sensor properties but also contamination effects, lead lengths, immersion,heat transfer, and controller interfacing. In temperature control, there are many sources of errorthat can be minimized by careful consideration of the type of sensor, its working environment, thesheath or housing, extension leads, and the instrumentation. An awareness of potential errors isvital in many applications dealt with in this book. Selection of temperature measurement devices isa complex task and has been discussed only briefly here. It is important to remember the following:“choose the right tool for the right job.”

1.3.4 Specific Volume and Density

The specific volume v is the volume per unit mass of a substance, usually expressed in cubic metersper kilogram (m3/kg) in the SI system and in cubic feet per pound (ft3/lb) in the English system.The density ρ of a substance is defined as the mass per unit volume, and is therefore the inverseof the specific volume:

ρ = 1v

(1.5)

The units of density are kg/m3 in the SI system and lb/ft3 in the English system. Specific volumeis also defined as the volume per unit mass, and density as the mass per unit volume, that is,

v = Vm

(1.6)

ρ = mV

(1.7)

Both specific volume and density are intensive properties and are affected by temperatureand pressure.

1.3.5 Mass and Volumetric Flow Rates

Mass flow rate is defined as the mass flowing per unit time (kg/s in the SI system and lb/s in theEnglish system). Volumetric flow rates are given in m3/s in the SI system and ft3/s in the Englishsystem. The following expressions can be written for the flow rates in terms of mass, specificvolume, and density:

ṁ = V̇ ρ = V̇v

(1.8)

V̇ = ṁv = ṁρ

(1.9)

General Introductory Aspects for Thermal Engineering 7

1.4 General Aspects of ThermodynamicsIn this section, we briefly introduce some general aspects of thermodynamics that are related toenergy storage systems and applications.

1.4.1 Thermodynamic Systems

A thermodynamic system is a device or combination of devices that contains a certain quantity ofmatter. It is important to carefully define a system under consideration and its boundaries. We candefine three important types of systems as follows:

• Closed system. This is defined as a system across the boundaries of which no material crosses.It, therefore, contains a fixed quantity of matter. In some books, it is also called a control mass .

• Open system. This is defined as a system in which material (mass) is allowed to cross itsboundaries. The term open system is also called a control volume.

• Isolated system. This is a closed system that is not affected by the surroundings. No mass, heat,or work crosses its boundary.

1.4.2 Process

A process is a physical or chemical change in the properties of matter or the conversion of energyfrom one form to another. In some processes, one property remains constant. The prefix “iso”is employed to describe such a process, for example, isothermal (constant temperature), isobaric(constant pressure), and isochoric (constant volume).

1.4.3 Cycle

A cycle is a series of thermodynamic processes in which the end-point conditions or properties ofthe matter are identical to the initial conditions.

1.4.4 Thermodynamic Property

This is a physical characteristic of a substance, which is used to describe its state. Any two propertiesusually define the state or condition of a substance, from which all other properties can be derived.Some examples are temperature, pressure, enthalpy, and entropy. Thermodynamic properties areclassified as intensive properties (independent of the mass, e.g., pressure, temperature, and density)and extensive properties (dependent on the mass, e.g., mass and total volume). Extensive propertieson a per unit mass basis, such as specific volume, become intensive properties. Property diagrams ofsubstances can be presented in graphical form and summarize the main properties listed in propertytables, for example, refrigerant tables.

1.4.5 Sensible and Latent Heats

It is known that all substances can hold a certain amount of heat; this property is their thermalcapacity. When a liquid is heated, its temperature rises to the boiling point. This is the highesttemperature that the liquid can reach at the measured pressure. The heat absorbed by the liquid inraising the temperature to the boiling point is called sensible heat . The heat required to convert theliquid to vapor at the same temperature and pressure is called latent heat . This is the change in

8 Thermal Energy Storage

enthalpy during a state change (the amount of heat absorbed or rejected at constant temperature atany pressure, or the difference in enthalpies of a pure condensable fluid between its dry saturatedstate and its saturated liquid state at the same pressure).

1.4.6 Latent Heat of Fusion

Fusion is associated with the melting and freezing of a material. For most pure substances, thereis a specific melting/freezing temperature, relatively independent of the pressure. For example, icebegins to melt at 0 ◦C. The amount of heat required to melt one kilogram of ice at 0 ◦C to onekilogram of water at 0 ◦C is called the latent heat of fusion of water, and equals 334.92 kJ/kg. Theremoval of the same amount of heat from one kilogram of water at 0 ◦C changes it back to ice.

1.4.7 Vapor

A vapor is a gas at or near equilibrium with the liquid phase – a gas under the saturation curveor only slightly beyond the saturated vapor line. Vapor quality is theoretically assumed; that is,when vapor leaves the surface of a liquid, it is pure and saturated at the particular temperature andpressure. In actuality, tiny liquid droplets escape with the vapor. When a mixture of liquid andvapor exists, the ratio of the mass of the liquid to the total mass of the liquid and vapor mixture iscalled the quality , and is expressed as a percentage or decimal fraction. Superheated vapor is thesaturated vapor to which additional heat has been added, raising the temperature above the boilingpoint. Let us consider a mass m with a quality x. The volume is the sum of the volumes of boththe liquid and the vapor, as defined below:

V = Vliq + Vvap (1.10)Equation 1.10 can also be written in terms of specific volumes as

mv = mliqvliq + mvapvvap (1.11)Dividing all terms by the total mass yields

v = (1 − x)vliq + xvvap = vliq + xvliq,vap (1.12)where vliq,vap = vvap − vliq.

1.4.8 Thermodynamic Tables

The thermodynamic tables were first published in 1936 as steam tables by Keenan and Keyes, andlater in 1969 and 1978, these were revised and republished. The use of thermodynamic tables ofmany substances ranging from water to refrigerants is very common in process design calculations.In the literature, they are also called either steam tables or vapor tables . In this book, we willrefer to the thermodynamic tables. These tables are normally given as different distinct phases(parts), for example, four different parts for water, such as saturated water, superheated vaporwater, compressed liquid water, saturated solid-saturated vapor water; and two distinct parts forR-134a, such as saturated and superheated. Each table is listed according to the values of temperatureand pressure, with the remainder containing values of various other thermodynamic parameters suchas specific volume, internal energy, enthalpy, and entropy. Normally, when we have values for twoindependent variables, we may obtain other data from the respective table. In learning how to usethese tables, an important point is to specify the state using any two independent parameters. Insome design calculations if we do not have the exact values of the parameters, we use interpolationto find the necessary values.