Optimization of Solar Thermal Collector Systems for the Tropics

Abstract

Using experimental data and the TRNSYS (a transient system simulation program) simulation environment the behavior of solar thermal system is studied under various conditions. One system consists of evacuated tube collectors having aperture area of 15 m2 and a storage tank of volume 0.315 m3. Firstly, the system is modeled with TRNSYS and several independent variables like ambient temperature, solar irradiance etc. are used as inputs. Outputs of the simulation (e.g. collector outlet temperature, tank temperature etc.) are then compared with the experimental results. After successful validation, the prepared model is utilized to determine the optimum operating conditions for the system to supply the regeneration heat required by a special air dehumidification unit installed at the laboratory of the Solar Energy Research Institute of Singapore (SERIS). Using the meteorological data of Singapore, provided by SERIS, the annual solar fraction of the system is calculated. An economic analysis based on Singapore?s electricity prices is presented and the scheme of payback period and life cycle savings is used to find out the optimum parameters of the system. The pump speeds of the solar collector installation are set within the prescribed limits set by the American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) and optimized in order to meet the energy demand. Finally, the annual average system efficiency of the solar heat powered dehumidification system is calculated and found to be 26%; the system achieves an annual average solar fraction of 0.78. Furthermore, a stand-alone flat plate collector system is also studied under the meteorological condition of Singapore. The system comprises 1.87 m2 of collector area and a storage tank of 0.181 m3. A TRNSYS simulation model of the system is prepared and also validated with the experimental data. An economic analysis is also done for the flat plate collectors. The system is then optimized with the flat plate collectors to supply the heat, required for the regeneration process of the desiccant dehumidifier, on the basis of payback period and life cycle savings. Finally, a methodology is developed to test an evacuated tube collector and determine its various parameters in the user end. For this, a dynamic model of the evacuated tube collector is prepared with the MATLAB simulation environment. A successful validation of the dynamic model leads to the determination of various collector parameters. The validated model is also utilized to acquire the collector?s characteristic efficiency curves and to estimate its performance under different ambient conditions.