Performance analysis of an R290 vapor-injection heat pump system for electric vehicles in cold regions

High-performance automotive thermal management systems with environment-friendly refrigerants are essential for achieving carbon peaking and carbon neutrality goals. In this study, an R290 vapor-injection heat pump system for electric vehicles is developed and experimentally investigated. The effects of refrigerant charge mass, injection pressure, and in-cabin air temperature are analyzed in ambient temperatures from −30°C to 0°C. The results show that the vapor-injection system can increase the coefficient of performance (COP) and heating capacity by 14.3% and 15.9% at 0°C/20°C (ambient/in-cabin temperature) compared with the basic system, and this increase becomes more significant at −20°C/20°C with improvements of 32.5% and 38.1%, respectively. At a lower ambient temperature of −20°C, increasing refrigerant charge mass contributes to a more pronounced increase in heating capacity than at 0°C, which results from the more significant increase in injection mass flow. The optimal COP at various injection pressures are 2.07 and 1.63 at 0°C and −20°C ambient temperatures, corresponding to the relative injection pressures of 0.60 and 0.57, and the injection flow ratios of 0.23 and 0.29, respectively. At −30°C/0°C, a COP of 1.69 can be achieved.