A solar-air hybrid source heat pump for space heating and domestic hot water

Traditional solar collectors (SCs) cannot effectively use solar energy of varying intensity, and air source heat pumps cannot supply heat steadily during defrosting conditions. Accordingly, a solar-air hybrid source heat pump (HSHP) system is proposed to solve these problems. A SC was indirectly connected to a heat pump evaporator and water tank for a user at the same time, to allow direct heating when the solar energy is abundant and to supply heat to the heat pump. Multiple air heat exchangers were also connected indirectly to the heat pump. When one of these is in defrosting mode, the others can still work to guarantee a continuous heat output. The structure and operation strategies are introduced, and a numerical model is established to evaluate the performance of the solar-air HSHP. The performance was also compared with a traditional SC plus an air source heat pump (SC + ASHP). The results show that: (1) the heat provided by the solar-air source heat pump mode is 15%, 11%, and 12% of the total heat production in Chengdu, Beijing, and Shenyang, respectively, which indicates that weak solar radiation can also be used effectively; (2) the energy for defrosting using a solar-air HSHP is only between 30% and 36% of that when using a SC + ASHP system, and between 16% and 35% of that in the ASHP system, which indicates a large energy savings potential of the system in defrosting conditions; and (3) the seasonal performance factor (SPF) during a heating season is 3.61, 3.27, and 2.45 in Chengdu, Beijing, and Shenyang, respectively, and it can reach up to 6.92 in Lhasa due to sufficient solar energy resources.