Solar assisted R22 and R134a heat pump systems for low temperature applications

The results of the simulations for a conventional heat pump, a conventional solar air heater and two serial solar-assisted heat pump (SAHP) systems are presented in this paper. The thermodynamic properties of R22, R404a and R134a are given in the form of correlations with correlation factors higher than 0.99. The performance characteristics of the heat pump are investigated using these working refrigerants, for wide ranges of evaporator temperature (0-45°C), condenser temperature (50-70°C) and air mass flow rates (500-2000 kg/hr). The comparison of the heat pump performance for the considered working refrigerants proved that R134a is the most promised alternative to R22 for low temperature applications. This is confirmed by a 22% increase in the coefficient of performance for R134a over R404a. The operating conditions and the performance of both the conventional solar air heater and SAHP systems have been evaluated round the year using the meteorological data of Cairo (latitude of 30°N). Comparison between performance of the SAHP systems, conventional heat pumps or conventional solar air heaters, shows that the SAHP systems provide better characteristics over these conventional systems. Moreover, the SAHP system in which heated air flows from the collector to the evaporator, and then through the condenser, is preferable. This system using R134a gives an increase of more than 50% in the coefficient of performance of the heat pump and a saving of 21% in the collector area