Development of the effective defrosting criterion for electric vehicles transcritical CO₂ heat pumps under constant heating capacity operation

Passenger comfort takes precedence over heating performance for electric vehicle heat pumps. However, frost formation will cause the heat exchange performance to decrease, leading to the heating capacity dissipation. The dynamics of an electric vehicle CO₂ heat pump under constant heating capacity operation during the frosting process were revealed. Moreover, it was found that the dynamic characteristics of parameters under constant heating capacity operation were significantly different from those under constant compressor speed operation. The application of defrosting initiation judgment criteria based on traditional heat pumps to electric vehicle heat pumps would lead to some serious false defrosting phenomena and even damage the compressor and pipelines. Therefore, a new defrosting initiation criterion was proposed for electric vehicle heat pumps based on the dynamic characteristics. Then, the reliability of the new initiation was verified by applying it in different heating demand operations. Finally, the average performance of electric vehicle heat pumps adopting the new defrost initiation was compared with the traditional PTC auxiliary heating method. The conclusion demonstrated that the heat pump with the new defrost initiation criterion had obvious performance advantages under different environmental conditions.