The performance of a solar assisted heat pump water heating system

Analytical and experimental studies were performed on a solar assisted heat pump water heating system, where unglazed, flat plate solar collectors act ed as an evaporator for the refrigerant R-134a. The system was designed and fabricated locally, and operated under meteorological conditions of Singap ore. The results obtained from simulation are used for the optimum design o f the system and enable determination of compressor work, solar fraction an d auxiliary energy required for a particular application. To ensure proper matching between the collector/evaporator load and compressor capacity, a v ariable speed compressor was used. Due to high ambient temperature in Singa pore, evaporator can be operated at a higher temperature, without exceeding the desired design pressure limit of the compressor, resulting in an impro ved thermal performance of the system. Results show that, when water temper ature in the condenser tank increases with time? the condensing temperature , also, increases, and the corresponding COP and collector efficiency value s decline. Average values of COP ranged from about 4 to 9 and solar collect or efficiency was found to vary between 40% and 75% for water temperatures in the condenser tank varying between 30 degreesC and 50 degreesC. A simula tion model has been developed to analyse the thermal performance of the sys tem. A series of numerical experiments have been performed to identify impo rtant variables. These results are compared with experimental values and a good agreement between predicted and experimental results has been found. R esults indicate that the performance of the system is influenced significan tly by collector area, speed of the compressor, and solar irradiation. An e conomic analysis indicates a minimum payback period of about two years for the system. (C) 2001 Elsevier Science Ltd. All rights reserved.