The Design and Sizing of Active Solar Thermal Systems T. AGAMIREDDY Division of Energy Technology, Asian Institute of Technology, Bangkok, Thailand CLARENDON PRESS OXFORD 1987
Nomenclature Copyright permissions xviii xxiv 1. Deseription of solar thennal systems 1 1.1. Introduction 1 1.2. Oassification of solar thermal systems 1 1.2.1. Stand-alone solar energy systems 2 1.2.2. Solar-supplemented energy systems 2 1.2.3. Passive systems 2 1.2.4. Active systems 3 1.2.5. Domestic and industrial systems 3 1.2.6. Liquid and air collectors 3 1.2.7. Daily and seasonal storage 5 1.3. Different active system configurations 5 1.4. Controls in solar thermal systems 13 2. ModelHng of solar thennal system components and simnlation procedure 18 2.1. Introduction 18 2.2. Solar collection subsystem 18 2.2.1. Solar collector model 18 2.2.2. Incidence angle modifier 21 2.2.3. Determination of collector performance parameters 21 2.2.4. Combined collector-heat exchanger performance 24 2.2.5. Other corrections 25 2.3. Storage subsystem 30 2.3.1. Thermal losses from storage 30 2.3.2. Water storage models 31 2,4. Load subsystem 36 2.4.1. Load heat exchanger performance 36 2.4.2. Relief valves 37 2.4.3. Types of thermal loads 37 2.4.4. Solar fraction 40 2.5. Procedure of simulation 41 2.6. Relative performance of closed-loop and open-loop systems 49 --------- --.~-...--------
xiv 3. Economic analysis 57 3.1. Introduction 57 3.2. Production functions 57 3.3. A simplified methodology for economic analysis 60 3.3.1. Basic concepts 60 3.3.2. Initial cost 61 3.3.3. Operating costs 61 3.3.4. Discounted total savings 64 4. Estimation of solar radiation 72 4.1. Introduction 72 4.2. Determination of radiation on horizontal surfaces 73 4.2.1. Prediction of monthly average daily horizontal global radiation 73 4.2.2. Prediction of monthly average daily horizontal diffuse radiation from monthly average daily horizontal global radiation 75 4.2.3. Prediction of daily horizontal global radiation from monthly average daily horizontal global radiation 75 4.2.4. Prediction of daily horizontal diffuse radiation from daily horizontal global radiation 81 4.2.5. Prediction of hourly horizontal global radiation from daily horizontal global radiation 84 4.2.6. Prediction of hourly horizontal diffuse radiation 84 4.2.7. General remarks 86 4.3. Conversion of radiation to tilted surfaces 89 4.3.1. Conversion factor for hourly radiation 90 4.3.2. Conversion factor for daily radiation 90 4.4. Total radiation on a tilted surface during a specified time interval % 4.5. Modelling of diurnal radiation as a sinusoid 98 4.6. Optimum tilt angle for flat-plate solar collectors 103 4.7. Estimation of the optical characteristics of flat-plate collectors for solar radiation 106 5. Long-tenn pedonnance of solar couectors U4 5.1. Solar collector performance under different operating conditions 114 5.1.1. Collector fluid inlet temperature variable over the sunshine hours of a day and over the days of the month 114 5.1.2. Collector fluid inlet temperature constant over the
sunshine hours of a day but variable over the days of the month 115 5.1.3. Collector fluid inlet temperature variable over the sunshine hours of a day but constant over the days of the month 116 5.1.4. Collector fluid inlet temperature constant over the sunshine hours of a day and over the days of the month 119 5.1.5. Collector fluid inlet temperature constant over all the sunshine hours of the year 122 5.2. Mathematical insight into the utilizability function 127 5.3. Generalized 1;1tilizability 134 5.3.1. Generalized hourly utilizability 134 5.3.2. Generalized daily utilizability 138 5.3.3. Daily utilizability method proposed by Evans et al. 143 5.3.4. Collector performance over the year 146 5.4. Concluding remarks 155 6. Application of utilizabuity methods to solar thennal system pedonnance determination 159 6.1. Introduction 159 6.2. Simple no-storage solar thermal systems 159 6.3. No-storage solar thermal systems with heat exchanger 169 6.4. Simulation of solar thermal systems with seasonal storage 170 6.5. Concluding remarks 177 6.5.1. Effect of the clearness index of the location 178 6.5.2. Compatibility of the various utilizability correlations 180 6.5.3. Effect of incidence angle modifier 184 7. Prediction of solar thennal system pedonnance by the empirical correlation approach 187 7.1. Introduction 187 7.2. The f--chart method 188 7.3. The phibar-f chart method for systems with auxiliary heater in parallel 196 7.4. The phibar-f chart method for systems with auxiliary heater in series 203 7.5: Some design aspects of closed-loop system configurations 211 7.5.1. Auxiliary heater: parallel vs. series arrangement 211 7.5.2. Effect of load distribution 212 7.5.3. Effect of storage size 212 7.5.4. Use of correlation outside the allowable range 213 7.6. Concluding remarks 214 xv
xvi 8. Design of solar thermal systems by the simplified analytical approach 219 8.1. Introduction 219 8.2. Solar industrial hot-water systems without heat storage 220 8.3. Solar industrial hot-water systems with heat storage 227 8.4. Generation of solar collector production functions 237 8.5. Concluding remarks 247 9. Prediction of solar thermal system penormance by the simplified system simulation approach using one-repetitive-day methods 249 9.1. Introduction 249 9.1.1. Semi-analytical numerical simulation procedure 249 9.1.2. Stochastic procedure 250 9.1.3. Procedure involving simulation over representative days 250 9.2. Rationale of the one-repetitive-day methods 250 9.3. The typical meteorological day (TMD) method 252 9.4. The MIRA method 259 9.5. Accuracy of the TMD and MIRA methods 263 9.5.1. Choice of convergence tolerance 263 9.5.2. Range of accuracy 265 9.6. Versatility of the one-repetitive-day methods 266 9.6.1. Closed-loop versus open-loop solar thermal system configurations 266 9.6.2. Effect of storage stratification on solar thermal system performance 270 9.6.3. Variable thermal loads 271 9.7. Generation of radiation forcing functions 277 9.7.1. For the TMD method 277 9.7.2. For the MIRA method 282 9.8. Concluding remarks 287 10. Concluding remarks on design methods and solar thermal systems 292 10.1. The need for design methods 292 10.2. Basic approaches of design methods 292 10.3. Practical considerations in system design 297 10.4. Potential applications of solar thermal systems 298 Appendix A. Sun-earth astronomical concepts and relations A.l. Introduction A.2. Basic sun-earth angles A.3. Solar angles 304 304 306 307
I I Appendix i AA. Angles of incidence A.5. Solar time A.6. Extraterrestrial solar radiation A.7. Conversion factors for extraterrestrial radiation A.7.1. Instantaneous ( or hourly) conversion factors for tilted surfaces A.7.2. Daily conversion factors for equator-facing tilted surfaces A.7.3. Daily conversion factors for tilted surfaces of arbitrary orientation Appendix B. Long-tenn pedonnance or concentrating solar collectors B.1. Introduction B.2. Qassification B.2.1. Non-concentrating collectors with fixed aperture B.2.2. Concentrators with fixed aperture and equatorfacing B.2.3. One-axis tracker about east-west horizontal axis B.2.4. One-axis tracker about north-south axis B.2.5. Two-axis tracker B.3. Monthly performance B.4. Yearly performance Appendix C. Solar thennal systems ror hot-air app6cations C.1. Introduction C.2. Solar air collectors C.3. Solar air systems C.3.1. Liquid-based systems C.3.2. Air-based systems CA. Design methods for solar hot-air systems D. Meteorological data ror selected locations or the world Appendix E. Development or a solar computer package Appendix F. Useful conversion ractors Index xvii 310 313 314 316 316 317 318 320 320 320 321 321 328 332 332 332 339 341 343 347 357 376 383 387 I ---_..._-_..