The Design and Sizing of Active Solar Thermal Systems

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1 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

2 Nomenclature Copyright permissions xviii xxiv 1. Deseription of solar thennal systems Introduction Oassification of solar thermal systems Stand-alone solar energy systems Solar-supplemented energy systems Passive systems Active systems Domestic and industrial systems Liquid and air collectors Daily and seasonal storage Different active system configurations Controls in solar thermal systems ModelHng of solar thennal system components and simnlation procedure Introduction Solar collection subsystem Solar collector model Incidence angle modifier Determination of collector performance parameters Combined collector-heat exchanger performance Other corrections Storage subsystem Thermal losses from storage Water storage models 31 2,4. Load subsystem Load heat exchanger performance Relief valves Types of thermal loads Solar fraction Procedure of simulation Relative performance of closed-loop and open-loop systems ~

3 xiv 3. Economic analysis Introduction Production functions A simplified methodology for economic analysis Basic concepts Initial cost Operating costs Discounted total savings Estimation of solar radiation Introduction Determination of radiation on horizontal surfaces Prediction of monthly average daily horizontal global radiation Prediction of monthly average daily horizontal diffuse radiation from monthly average daily horizontal global radiation Prediction of daily horizontal global radiation from monthly average daily horizontal global radiation Prediction of daily horizontal diffuse radiation from daily horizontal global radiation Prediction of hourly horizontal global radiation from daily horizontal global radiation Prediction of hourly horizontal diffuse radiation General remarks Conversion of radiation to tilted surfaces Conversion factor for hourly radiation Conversion factor for daily radiation Total radiation on a tilted surface during a specified time interval % 4.5. Modelling of diurnal radiation as a sinusoid Optimum tilt angle for flat-plate solar collectors Estimation of the optical characteristics of flat-plate collectors for solar radiation Long-tenn pedonnance of solar couectors U Solar collector performance under different operating conditions Collector fluid inlet temperature variable over the sunshine hours of a day and over the days of the month Collector fluid inlet temperature constant over the

4 sunshine hours of a day but variable over the days of the month Collector fluid inlet temperature variable over the sunshine hours of a day but constant over the days of the month Collector fluid inlet temperature constant over the sunshine hours of a day and over the days of the month Collector fluid inlet temperature constant over all the sunshine hours of the year Mathematical insight into the utilizability function Generalized 1;1tilizability Generalized hourly utilizability Generalized daily utilizability Daily utilizability method proposed by Evans et al Collector performance over the year Concluding remarks Application of utilizabuity methods to solar thennal system pedonnance determination Introduction Simple no-storage solar thermal systems No-storage solar thermal systems with heat exchanger Simulation of solar thermal systems with seasonal storage Concluding remarks Effect of the clearness index of the location Compatibility of the various utilizability correlations Effect of incidence angle modifier Prediction of solar thennal system pedonnance by the empirical correlation approach Introduction The f--chart method The phibar-f chart method for systems with auxiliary heater in parallel The phibar-f chart method for systems with auxiliary heater in series : Some design aspects of closed-loop system configurations Auxiliary heater: parallel vs. series arrangement Effect of load distribution Effect of storage size Use of correlation outside the allowable range Concluding remarks 214 xv

5 xvi 8. Design of solar thermal systems by the simplified analytical approach Introduction Solar industrial hot-water systems without heat storage Solar industrial hot-water systems with heat storage Generation of solar collector production functions Concluding remarks Prediction of solar thermal system penormance by the simplified system simulation approach using one-repetitive-day methods Introduction Semi-analytical numerical simulation procedure Stochastic procedure Procedure involving simulation over representative days Rationale of the one-repetitive-day methods The typical meteorological day (TMD) method The MIRA method Accuracy of the TMD and MIRA methods Choice of convergence tolerance Range of accuracy Versatility of the one-repetitive-day methods Closed-loop versus open-loop solar thermal system configurations Effect of storage stratification on solar thermal system performance Variable thermal loads Generation of radiation forcing functions For the TMD method For the MIRA method Concluding remarks Concluding remarks on design methods and solar thermal systems The need for design methods Basic approaches of design methods Practical considerations in system design 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

6 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 I ---_..._-_..