Solar Engineering of Thermal Processes

928 Pages·2013·5.86 MB·English

by  John A. Duffie, William A. Beckman

Solar Engineering
of Thermal Processes
Solar Engineering
of Thermal Processes
Fourth Edition
John A. Duffie (Deceased)
Emeritus Professor of Chemical Engineering
William A. Beckman
Emeritus Professor of Mechanical Engineering
Solar Energy Laboratory
University of Wisconsin-Madison
Cover image: (top) Kyu Oh/iStockphoto; (bottom) Gyula Gyukli/iStockphoto
Cover design: Anne-Michele Abbott
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Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
Contents
Preface xi 2.12 Beam and Diffuse Components of Monthly
Preface to the Third Edition xiii Radiation 79
Preface to the Second Edition xv 2.13 Estimation of Hourly Radiation from Daily
Preface to the First Edition xvii Data 81
Introduction xxi 2.14 Radiation on Sloped Surfaces 84
2.15 Radiation on Sloped Surfaces: Isotropic
Sky 89
PART I FUNDAMENTALS 1 2.16 Radiation on Sloped Surfaces: Anisotropic
Sky 91
2.17 Radiation Augmentation 97
1 Solar Radiation 3
2.18 Beam Radiation on Moving Surfaces 101
1.1 The Sun 3 2.19 Average Radiation on Sloped Surfaces: Isotropic
1.2 The Solar Constant 5 Sky 103
1.3 Spectral Distribution of Extraterrestrial 2.20 Average Radiation on Sloped Surfaces:
Radiation 6 KT Method 107
1.4 Variation of Extraterrestrial Radiation 8 2.21 Effects of Receiving Surface Orientation
1.5 Definitions 9 on HT 112
1.6 Direction of Beam Radiation 12 2.22 Utilizability 115
1.7 Angles for Tracking Surfaces 20 2.23 Generalized Utilizability 118
1.8 Ratio of Beam Radiation on Tilted Surface 2.24 Daily Utilizability 126
to That on Horizontal Surface 23 2.25 Summary 132
1.9 Shading 29 References 133
1.10 Extraterrestrial Radiation on a Horizontal
Surface 37
1.11 Summary 41 3 Selected Heat Transfer Topics 138
References 41
3.1 The Electromagnetic Spectrum 138
3.2 Photon Radiation 139
2 Available Solar Radiation 43 3.3 The Blackbody: Perfect Absorber and
Emitter 139
2.1 Definitions 43 3.4 Planck’s Law and Wien’s Displacement
2.2 Pyrheliometers and Pyrheliometric Scales 44 Law 140
2.3 Pyranometers 48 3.5 Stefan-Boltzmann Equation 141
2.4 Measurement of Duration of Sunshine 53 3.6 Radiation Tables 142
2.5 Solar Radiation Data 54 3.7 Radiation Intensity and Flux 144
2.6 Atmospheric Attenuation of Solar 3.8 Infrared Radiation Exchange between Gray
Radiation 59 Surfaces 146
2.7 Estimation of Average Solar Radiation 64 3.9 Sky Radiation 147
2.8 Estimation of Clear-Sky Radiation 68 3.10 Radiation Heat Transfer Coefficient 148
2.9 Distribution of Clear and Cloudy Days 3.11 Natural Convection between Flat Parallel Plates
and Hours 71 and between Concentric Cylinders 149
2.10 Beam and Diffuse Components of Hourly 3.12 Convection Suppression 154
Radiation 74 3.13 Vee-Corrugated Enclosures 158
2.11 Beam and Diffuse Components of Daily 3.14 Heat Transfer Relations for Internal
Radiation 77 Flow 159
v
vi Contents
3.15 Wind Convection Coefficients 163 6 Flat-Plate Collectors 236
3.16 Heat Transfer and Pressure Drop in Packed
6.1 Description of Flat-Plate Collectors 236
Beds and Perforated Plates 165
6.2 Basic Flat-Plate Energy Balance
3.17 Effectiveness-NTU Calculations for Heat
Equation 237
Exchangers 168
6.3 Temperature Distributions in Flat-Plate
References 170
Collectors 238
6.4 Collector Overall Heat Loss Coefficient 240
4 Radiation Characteristics of Opaque 6.5 Temperature Distribution between Tubes and the
Materials 173 Collector Efficiency Factor 254
6.6 Temperature Distribution in Flow
4.1 Absorptance and Emittance 174
Direction 261
4.2 Kirchhoff’s Law 176
6.7 Collector Heat Removal Factor and Flow
4.3 Reflectance of Surfaces 177
Factor 262
4.4 Relationships among Absorptance, Emittance,
6.8 Critical Radiation Level 266
and Reflectance 181
6.9 Mean Fluid and Plate Temperatures 267
4.5 Broadband Emittance and Absorptance 182
6.10 Effective Transmittance-Absorptance
4.6 Calculation of Emittance and
Product 268
Absorptance 183
6.11 Effects of Dust and Shading 271
4.7 Measurement of Surface Radiation
6.12 Heat Capacity Effects in Flat-Plate
Properties 186
Collectors 272
4.8 Selective Surfaces 188
6.13 Liquid Heater Plate Geometries 275
4.9 Mechanisms of Selectivity 192
6.14 Air Heaters 280
4.10 Optimum Properties 195
6.15 Measurements of Collector Performance 287
4.11 Angular Dependence of Solar
6.16 Collector Characterizations 288
Absorptance 196
6.17 Collector Tests: Efficiency, Incidence Angle
4.12 Absorptance of Cavity Receivers 197
Modifier, and Time Constant 289
4.13 Specularly Reflecting Surfaces 198
6.18 Test Data 299
References 199
6.19 Thermal Test Data Conversion 302
6.20 Flow Rate Corrections to FR(τα)n
and FR UL 305
5 Radiation Transmission through Glazing:
6.21 Flow Distribution in Collectors 308
Absorbed Radiation 202
6.22 In Situ Collector Performance 309
6.23 Practical Considerations for Flat-Plate
5.1 Reflection of Radiation 202
Collectors 310
5.2 Absorption by Glazing 206
6.24 Putting it all Together 313
5.3 Optical Properties of Cover
6.25 Summary 318
Systems 206
References 319
5.4 Transmittance for Diffuse
Radiation 211
5.5 Transmittance-Absorptance Product 213
7 Concentrating Collectors 322
5.6 Angular Dependence of (τα) 214
5.7 Spectral Dependence of Transmittance 215 7.1 Collector Configurations 323
5.8 Effects of Surface Layers on 7.2 Concentration Ratio 325
Transmittance 218 7.3 Thermal Performance of Concentrating
5.9 Absorbed Solar Radiation 219 Collectors 327
5.10 Monthly Average Absorbed Radiation 223 7.4 Optical Performance of Concentrating
5.11 Absorptance of Rooms 229 Collectors 334
5.12 Absorptance of Photovoltaic Cells 231 7.5 Cylindrical Absorber Arrays 335
5.13 Summary 234 7.6 Optical Characteristics of Nonimaging
References 234 Concentrators 337
Contents vii
7.7 Orientation and Absorbed Energy for CPC 10.4 Controls 429
Collectors 345 10.5 Collector Arrays: Series Connections 431
7.8 Performance of CPC Collectors 349 10.6 Performance of Partially Shaded
7.9 Linear Imaging Concentrators: Geometry 351 Collectors 433
7.10 Images Formed by Perfect Linear 10.7 Series Arrays with Sections Having Different
Concentrators 354 Orientations 435
7.11 Images from Imperfect Linear 10.8 Use of Modified Collector Equations 438
Concentrators 359 10.9 System Models 441
7.12 Ray-Trace Methods for Evaluating 10.10 Solar Fraction and Solar Savings
Concentrators 361 Fraction 444
7.13 Incidence Angle Modifiers and Energy 10.11 Summary 445
Balances 361 References 446
7.14 Paraboloidal Concentrators 367
7.15 Central-Receiver Collectors 368
7.16 Practical Considerations 369 11 Solar Process Economics 447
References 370
11.1 Costs of Solar Process Systems 447
11.2 Design Variables 450
8 Energy Storage 373 11.3 Economic Figures of Merit 452
11.4 Discounting and Inflation 454
8.1 Process Loads and Solar Collector 11.5 Present-Worth Factor 456
Outputs 373 11.6 Life-Cycle Savings Method 459
8.2 Energy Storage in Solar Process Systems 375 11.7 Evaluation of Other Economic
8.3 Water Storage 376 Indicators 464
8.4 Stratification in Storage Tanks 379 11.8 The P
1, P2 Method 467
8.5 Packed-Bed Storage 384 11.9 Uncertainties in Economic Analyses 472
8.6 Storage Walls 392 11.10 Economic Analysis Using Solar Savings
8.7 Seasonal Storage 394 Fraction 475
8.8 Phase Change Energy Storage 396 11.11 Summary 476
8.9 Chemical Energy Storage 400 References 476
8.10 Battery Storage 402
References 406
PART II APPLICATIONS 477
9 Solar Process Loads 409
12 Solar Water Heating: Active and
9.1 Examples of Time-Dependent Loads 410
Passive 479
9.2 Hot-Water Loads 411
9.3 Space Heating Loads, Degree-Days,
12.1 Water Heating Systems 479
and Balance Temperature 412
12.2 Freezing, Boiling, and Scaling 483
9.4 Building Loss Coefficients 415
12.3 Auxiliary Energy 486
9.5 Building Energy Storage Capacity 417
12.4 Forced-Circulation Systems 488
9.6 Cooling Loads 417
12.5 Low-Flow Pumped Systems 490
9.7 Swimming Pool Heating Loads 418
12.6 Natural-Circulation Systems 491
References 420
12.7 Integral Collector Storage Systems 494
12.8 Retrofit Water Heaters 496
12.9 Water Heating in Space Heating and Cooling
10 System Thermal Calculations 422
Systems 497
10.1 Component Models 422 12.10 Testing and Rating of Solar Water
10.2 Collector Heat Exchanger Factor 424 Heaters 497
10.3 Duct and Pipe Loss Factors 426 12.11 Economics of Solar Water Heating 499
viii Contents
12.12 Swimming Pool Heating 502 15.7 Solar Desiccant Cooling 592
12.13 Summary 503 15.8 Ventilation and Recirculation Desiccant
References 503 Cycles 594
15.9 Solar-Mechanical Cooling 596
15.10 Solar-Related Air Conditioning 599
13 Building Heating: Active 505
15.11 Passive Cooling 601
References 601
13.1 Historical Notes 506
13.2 Solar Heating Systems 507
13.3 CSU House III Flat-Plate Liquid System 511
16 Solar Industrial Process Heat 604
13.4 CSU House II Air System 513
13.5 Heating System Parametric Study 517 16.1 Integration with Industrial Processes 604
13.6 Solar Energy–Heat Pump Systems 521 16.2 Mechanical Design Considerations 605
13.7 Phase Change Storage Systems 527 16.3 Economics of Industrial Process Heat 606
13.8 Seasonal Energy Storage Systems 530 16.4 Open-Circuit Air Heating Applications 607
13.9 Solar and Off-Peak Electric Systems 533 16.5 Recirculating Air System Applications 611
13.10 Solar System Overheating 535 16.6 Once-Through Industrial Water Heating 613
13.11 Solar Heating Economics 536 16.7 Recirculating Industrial Water Heating 615
13.12 Architectural Considerations 539 16.8 Shallow-Pond Water Heaters 617
References 541 16.9 Summary 619
References 619
14 Building Heating: Passive and Hybrid
17 Solar Thermal Power Systems 621
Methods 544
17.1 Thermal Conversion Systems 621
14.1 Concepts of Passive Heating 545
17.2 Gila Bend Pumping System 622
14.2 Comfort Criteria and Heating Loads 546
17.3 Luz Systems 624
14.3 Movable Insulation and Controls 546
17.4 Central-Receiver Systems 628
14.4 Shading: Overhangs and Wingwalls 547
17.5 Solar One and Solar Two Power Plants 630
14.5 Direct-Gain Systems 552
References 633
14.6 Collector-Storage Walls and Roofs 557
14.7 Sunspaces 561
14.8 Active Collection–Passive Storage Hybrid
18 Solar Ponds: Evaporative Processes 635
Systems 563
14.9 Other Hybrid Systems 565 18.1 Salt-Gradient Solar Ponds 635
14.10 Passive Applications 565 18.2 Pond Theory 637
14.11 Heat Distribution in Passive Buildings 571 18.3 Applications of Ponds 639
14.12 Costs and Economics of Passive 18.4 Solar Distillation 640
Heating 571 18.5 Evaporation 646
References 573 18.6 Direct Solar Drying 647
18.7 Summary 647
References 648
15 Solar Cooling 575
15.1 Solar Absorption Cooling 576
PART III DESIGN
15.2 Theory of Absorption Cooling 578
15.3 Combined Solar Heating and Cooling 584 METHODS 651
15.4 Simulation Study of Solar Air
Conditioning 585
19 Simulations in Solar Process Design 653
15.5 Operating Experience with Solar Cooling 589
15.6 Applications of Solar Absorption Air 19.1 Simulation Programs 653
Conditioning 591 19.2 Utility of Simulations 654
Contents ix
19.3 Information from Simulations 655 23 Design of Photovoltaic Systems 745
19.4 TRNSYS: Thermal Process Simulation
23.1 Photovoltaic Converters 746
Program 656
23.2 PV Generator Characteristics
19.5 Simulations and Experiments 663
and Models 747
19.6 Meteorological Data 663
23.3 Cell Temperature 757
19.7 Limitations of Simulations 666
23.4 Load Characteristics and Direct-Coupled
References 667
Systems 759
23.5 Controls and Maximum Power Point
20 Design of Active Systems: f -Chart 668 Trackers 763
23.6 Applications 764
20.1 Review of Design Methods 668
23.7 Design Procedures 765
20.2 The f -Chart Method 669
23.8 High-Flux PV Generators 770
20.3 The f -Chart for Liquid Systems 673
23.9 Summary 771
20.4 The f -Chart for Air Systems 679
References 771
20.5 Service Water Heating Systems 683
20.6 The f -Chart Results 685
20.7 Parallel Solar Energy-Heat Pump
24 Wind Energy 774
Systems 686
20.8 Summary 690 24.1 Introduction 774
References 690 24.2 Wind Resource 778
24.3 One-Dimensional Wind Turbine Model 786
24.4 Estimating Wind Turbine Average Power and
21 Design of Active Systems by Utilizability
Energy Production 791
Methods 692
24.5 Summary 796
References 796
21.1 Hourly Utilizability 693
21.2 Daily Utilizability 696
21.3 The φ, f -Chart Method 699
APPENDIXES 797
21.4 Summary 709
References 710
A Problems 797
22 Design of Passive and Hybrid Heating
Systems 711 B Nomenclature 856
22.1 Approaches to Passive Design 711
22.2 Solar-Load Ratio Method 712 C International System of Units 861
22.3 Unutilizability Design Method: Direct
Gain 721
D Meteorological Data 863
22.4 Unutilizability Design Method: Collector-Storage
Walls 727
22.5 Hybrid Systems: Active Collection with Passive
E Average Shading Factors for
Storage 736
Overhangs 870
22.6 Other Hybrid Systems 742
References 743 Index 887
Preface
This fourth edition emphasizes solar system design and analysis using simulations. The
design of many systems that use conventional energy sources (e.g., oil, gas, and electricity)
use a worst-case environmental condition—think of a building heating system. If the
system can maintain the building temperature during the coldest period, it will be able to
handle all less severe conditions. To be sure, even building heating systems are now using
simulations during the design phase. In addition to keeping the building comfortable during
the worst conditions, various design choices can be made to reduce annual energy use.
This and earlier editions of this book describe TRNSYS (pronounced Tran-sis), a
general system simulation program (see Chapter 19). Like all heating and air conditioning
systems, a solar system can be thought of as a collection of components. TRNSYS
has hundreds of component models, and the TRNSYS language is used to connect the
components together to form a system. Following the Preface to the First Edition is
the Introduction where a ready-made TRNSYS program (called CombiSys) is described
that simulates a solar-heated house with solar-heated domestic hot water. TRANSED, a
front-end program for TRNSYS is used so it is not necessary to learn how to develop
TRNSYS models to run CombiSys. CombiSys can be freely downloaded from the John
Wiley website (http://www.wiley.com/go/solarengineering4e).
CombiSys provides an input window where various design options can be selected
(e.g., the collector type and design, storage tank size, collector orientation, and a variety of
other choices). A series of simulation problems (identified with a prefix ‘‘S’’ followed by a
chapter number and then a problem number) have been added to the standard problems of
many chapters. The ‘‘S0’’ problems (that is, Chapter 0, the Introduction) require running
CombiSys and answering general questions that may require performing energy balances
and doing simple economic calculations. As new topics are discussed in this text new ‘‘S’’
problems are introduced, often with the objective to duplicate some aspect of CombiSys.
With this approach it is hoped that the student will understand the inner workings of a
simulation program and be made aware of why certain topics are introduced and discussed
in the text.
The purpose of studying and understanding any topic in engineering is to make the
next system better than the last. Part I in this study of solar systems contains 11 chapters
devoted to understanding the operation of components (e.g., the sun, collectors, storage
systems, loads, etc.). The results of these early chapters are mathematical models that allow
the designer to estimate component performance (in the TRNSYS language, the outputs)
for a given set of component conditions (i.e., TRNSYS inputs). It is easy to think of
collectors, storage tanks, photovoltaic arrays, and batteries as components, but here even
the sun and economics are treated as components. The sun component manipulates the
available (generally measured but sometimes estimated) solar radiation data to obtain the
needed solar radiation data on an arbitrarily oriented surface and in a desired time interval.
The time scale of reported solar data ranges from a few seconds to yearly. Sometimes we
even need to estimate the solar energy in a wavelength interval. The available measured
solar radiation data is typically energy rates (i.e., power) from a specified and easily
xi
xii Preface
calculated direction such as the ‘‘beam’’ radiation that comes directly from the sun and
the ‘‘diffuse’’ radiation that has been scattered in some generally unknown manner over
all parts of the sky. The mathematical model of the sun component must accommodate
these various input and output requirements. The final chapter in Part I covers economics.
Generally the objective of a solar system is to produce environmentally friendly power at
an acceptable cost. The familiar calculations of levelized cost per unit of energy and/or
life-cycle savings (versus some energy alternative) are not trivial since the time horizon
of a solar system can be multiple decades, requiring the estimates of far-future economic
conditions. The economic impact of externalities such as reduced pollutants is difficult to
evaluate since these costs are not easily monetized.
Part II, chapters 12 through 18, discusses various thermal systems that have been built,
the performance measured and the results published. They are descriptive chapters with the
intent of providing the reader with a feeling of what can be accomplished. Many of these
systems were built and tested during a time when governments were funding universities
and laboratories where a requirement was to make the results public. Most solar systems
today are privately funded and performance data is often difficult or impossible to obtain.
Chapters 19 through 22 of Part III are devoted to system design (sometimes called
system sizing). Before the late 1970s personal computers were not available so simulations
were done either by hand or on large main-frame computers and were very expensive.
Research into ‘‘designmethods’’ focused on the development of short-cut design assistance
to replace expensive simulations. The earliest example is from the early 1950s, which used
a radiation statistic called ‘‘utilizability’’ to assist in solar sizing (see Section 2.22 and
Chapter 21). The next step, the f -chart method (see Chapter 21) is from the mid-1970s and
used numerical experiments to develop correlations of the various nondimensional groups.
This process is not unlike laboratory experiments that are used to correlate dimensionless
heat transfer results (the Nusselt number) to dimensionless fluid parameters (Reynolds,
Prandtl, and Grashof numbers). The significant difference is that the experimental results
in the f -chart development were hundreds of detailed main-frame computer simulations
and were validated with a few year-long experiments. These design methods still have
a place in today’s engineering practice. They are extremely fast and thus provide an
inexpensive alternative to annual simulations, especially for small systems. Large (and
therefore expensive) systems can afford to be looked at using detailed simulations. Some
of the problems in these chapters compare the detailed simulations using TRNSYS with
the various design methods.
Chapters 23 and 24 of Part III cover sizing of photovoltaic (PV) and wind energy
systems. It is obvious that the solar radiation processing developed in Chapter 2 is very
important in the design and analysis of PV systems. The detailed physics of a solar cell
is complex, but it is not necessary to understand these details to design a PV system. The
current-voltage (I -V ) characteristics of cells are discussed in detail and a mathematical
I -V model is presented that is useful in design. Wind energy systems are introduced with a
simple analysis that leads to understanding of manufacturers wind turbine characteristics.
The performance of an isolated turbine is discussed, but interference of the wind patterns
with close-packed multiple turbines is not discussed.
WILLIAM A. BECKMAN
Madison, Wisconsin