Experimental study of a direct expansion solar-assisted heat pump (DX-SAHP) with finned-tube evaporator and comparison with conventional DX-SAHP

Direct expansion solar-assisted heat pump system (DX-SAHP) is proven to be an effective energy-saving application. Due to the fact that the traditional bare-plate type direct expansion solar-assisted heat pump occupies large footprint and is inefficient under low solar irradiation, a modified direct expansion solar-assisted heat pump system with finned-tube evaporator is designed and tested in the enthalpy difference lab with a solar simulator. The effects of ambient temperature, relative humidity, solar irradiation, and wind speed on the performance of the finned-tube type system are investigated. Furthermore, the performance of finned-tube type system and bare-plate type system is compared and analyzed under identical experimental conditions. It is revealed that raising ambient temperature, solar irradiation and wind speed can effectively improve the heating performance of the finned-tube type system. In comparative analysis, frosting enhances the overall performance of bare-plate type system, while the performance of finned-tube type system significantly declines due to the heat transfer deterioration caused by the frosting. The COP of finned-tube type system decreases from 1.72 to 1.54, when the relative humidity rises from 50% to 90%. For bare-plate type system, with the relative humidity rising from 70% to 90%, COP increases by 16.3%. (C) 2019 Elsevier B.V. All rights reserved.