Parametric analysis of the thermal performance of a direct-expansion solar-assisted heat pump system for water heating

Direct-expansion solar-assisted heat pumps (DX-SAHP) have been widely used in many applications including industrial and domestic water heating. These systems transfer energy from lower temperature source to a higher temperature source. In DX-SAHP systems, in order to optimize the heat transfer of solar radiation to the refrigerant, the flat plate solar collector is used as the evaporator. The present work is aimed at studying the effects of various parameters including solar radiation, ambient temperature,collector surface area, compressor speed and number of collector covers on the thermal performance of a DX-SAHP system. This system mainly employs a collector/evaporator with a surface area of 4 m2, an electrical rotary-type hermetic compressor, a hot water tank with the volume of 150 L and a thermostatic expansion valve. Rl34a is used as working fluid in the system. Comparisons between the simulation results and the experimental measurements show that the model is able to give satisfactory predictions