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 (0-4S°C), condenser temperature (50-70°C) and air
mass flow rates (500-2000 kgh). The comparison of the heat
pump performance for the considered working refrigerants proved
that, R134a is the most promised altemative to R22 for low
temperature applications. This is confirmed by 22% increase in
the coefficient of performance for R134a over R404a.