THERMAL PERFORMANCE OF A VARIABLE CAPACITY DIRECT EXPANSION SOLAR-ASSISTED HEAT-PUMP

A variable capacity direct expansion solar-assisted heat pump system i s developed and operated for domestic hot water application. The propo sed system employs a bare solar collector which also acts as the syste m evaporator. A variable frequency drive modulates the compressor spee d to maintain a proper matching between the heat pumping capacity of t he compressor and the evaporative capacity of the collector under wide ly varying ambient conditions. Experimental results indicate that the coefficient of performance of the system can be improved significantly by lowering the compressor speed as ambient temperature rises from wi nter to summer months. Experimentally measured system COPH and water s ide heat capacity rate are also in good agreement with theoretical pre dictions. (C) 1997 Elsevier Science Ltd.