Experimental investigation on the heating performance of a CO2 heat pump system with intermediate cooling for electric vehicles

This study proposed an improved CO2 heat pump system for electric vehicles by introducing the concept of two stage compression with intermediate cooling. A coefficient of performance optimal control strategy was proposed based on the discovered feature that the changing trend of the COP is consistent with that of the inlet temperature of the electronic expansion valve. Contrast experiments between the heat pump with intermediate cooling compressor and the basic heat pump were conducted. Result shows that the two stage compression with intermediate cooling contributes to 50-132% increment in the heating capacity and 18.9-61.9% improvement in the COP over the basic system as the ambient temperature decreases from 0 degrees C to -20 degrees C. The advantages increase with the decrease in ambient temperature. The typical COP of this system under -20 degrees C ambient temperature and 20 degrees C in-car temperatures condition is approximately 1.70 while the discharge temperature is controlled well within 100 degrees C.