Experimental performance of a vapor-injection CO2 heat pump system for electric vehicles in −30 °C to 50 °C range

Abstract

Efficient and wide-range heat pump system is essential to improve the driving range and comfort of electric vehicles. In this paper, a vapor-injection transcritical CO2 heat pump system with a flash tank for electric vehicles was built up, and the heating and cooling performance in a wide range from −30 °C to 50 °C were experimentally studied. The maximum coefficient of performance (COP) at −30 °C/ 20 °C was 1.45, and the maximum COP at 50 °C/ 27 °C was 1.08. By comparing with the basic system without injection, it was found that the heating performance of the vapor-injection system was significantly improved, and the lower the outdoor temperature, the greater the improvement. The COP and heating capacity of the vapor-injection system were increased by 45.5 % and 75.7 % respectively at −30 °C/ 20 °C. Under the cooling conditions, only when the outdoor temperature was lower than 40 °C, the vapor-injection system had an advantage, and the maximum increments of COP and cooling capacity at 35 °C/ 27 °C were 9.5 % and 16.8 %, respectively. Further, a relationship model between vapor injection and compressor structure and operating conditions was established according to the working principle of the twin rotary compressor. The experimental verification showed that the deviation was within 8 %, which could provide a basis for the construction of the CO2 vapor injection heat pump system model.