Experimental investigation and performance evaluation on a direct expansion solar-air source heat pump system

Abstract

Solar energy is the most important renewable energy source for achieving carbon neutrality. The problem of steady and efficient operation must be promptly addressed due to the inconsistent and variable nature of solar energy. This research proposes a multifunctional heat pump using the R417A refrigerant, which combines a direct expansion solar heat pump (DXSHP) with an air source heat pump (ASHP), resulting in a direct expansion sola-air source heat pump (DX-S/AS-HP). The system could operate in three modes: combined cooling and heating, domestic water heating, and space heating. The performance of solar heat pump and air source heat pump in different modes was compared, and the switching logic of different modes was developed accordingly, and the performance of the system at different working temperatures was analyzed. The results demonstrate that in combined cooling and heating mode, the system's average comprehension coefficient of performance (COP) could approach 6.0. In DX-SHP mode, the average COP for domestic water heating and space heating is 3.94 and 4.25, respectively, which is greater than the air source heat pump in similar working conditions. Switching from DX-SHP to ASHP for domestic water heating is only necessary when solar irradiation is less than 300 W m − 2, while switching to ASHP for space heating is only necessary when solar irradiation is absent. The greater the working temperature, the lower the COP. While the working temperature has little effect on thermal collecting efficiency.