Experimental performance analysis of evacuated tube type direct-expansion solar-assisted heat pump system

The direct-expansion solar-assisted heat pump (DX-SAHP) have proven to be one of the strategies in reducing energy consuming for domestic hot water supply. The poor pressure resistance of the collector, high heat loss from radiation for the traditional bare-plate type DX-SAHP limits its popularization and application. To solve this problem, a DX-SAHP system using evacuated tube type collector-evaporator was proposed in this post. System optimization can not only reduce operating costs, but also results in energy savings. Thus, a DX-SAHP prototype was established and tested under various running conditions to obtain the optimal running parameters. Based on experimental data, the impacts of refrigerant charge, solar radiation intensity, and ambient temperature on the performances of evacuated tube type DX-SAHP system are investigated and evaluated. The outcome indicates that this system coefficient of performance (COP) increases by 73.4% with the decrease of charge amount of refrigerant in the range of 5.66–6.67 kg. And, the average collector efficiency is 0.71 with a refrigerant charge of 5.66 kg. And, the optimal COP of this presented system is 5.27 when an ambient temperature, solar radiation intensity, and refrigerant charge are 26.3°C, 954.37 W/m2, and 5.56 kg, respectively.