Experimental investigation on the low temperature performance of a novel three-pressure air source heat pump

As people's demand for living comfort grows, the problems of conventional air source heat pumps (ASHPs) become more prominent in low-temperature and high-humidity environments: heating performance attenuation, low defrosting efficiency, and significant impact on indoor thermal comfort during defrosting. Existing literature usually focuses on only one or two of these issues, and few comprehensively cover them. Based on current literature, this paper proposes a novel multi-functional three-pressure ASHP that can cover the above three aspects with a series-parallel combination structure featuring dual compressors and dual cycles. This design enables switching multiple heating and defrosting modes through valve combination and improves performance through two-stage throttling and subcooling. An experimental platform is constructed to evaluate its operational performance. The experimental results show that: (1) In heating modes, the average heating capacity of the three-pressure cycle heating mode is 2897.15 W, and the average COP is 2.47, while these two data of the conventional cycle heating mode are 2393.65 W and 2.4, and the improvement rates of 20.4 % and 2.9 %, respectively. It also extends the high-efficiency heating period of the system, enables rapid heating at start-up, increases compressor suction and discharge pressure, and improvs system stability. (2) In defrosting modes, compared with the conventional defrosting cycle, the three-pressure defrosting cycle raises the condensation temperature faster, reduces the defrosting time from 448 s to 265 s (40.8 % shorter). The auxiliary defrosting cycle has little effect on indoor thermal comfort and less defrosting power consumption, with the power saving rate as high as 44.6 %. Overall, the novel three-pressure ASHP has a unique and innovative structure, significantly optimizing performance under low-temperature and frosting conditions and improving energy efficiency and comfort. The results of this study provide a new solution concept for the future development of ASHPs, offering significant reference value for further development and application.