Cycle performance study on cascade high temperature air source heat pump system

Abstract Conventional air source heat pumps face significant challenges in producing hot water above 70°C at an ambient temperature of -30°C. Cascade heat pump systems allow for the utilization of two working fluids within their optimal thermodynamic properties, enabling heating over large temperature rise—exceeding 100°C. This study established a cascade heat pump cycle model, compared the thermal performance of 10 working fluids, and screened a working fluid combination with good thermal performance under the premise of environmental protection and safety. When the low-temperature working fluid is R161 and the high-temperature working fluid is R142b, the coefficient of performance ( COP ) is above 2.14. The variable operating cycle performance of the R161/R142b cascade heat pump was analyzed. The condensing temperature is 40∼70°C, the evaporating temperature is 40∼70°C, and the system COP and compression ratio are both within a reasonable range.