Performance evaluation of transcritical CO2 desiccant heat pumps for electric vehicles

Transcritical CO2 heat pump systems are eco-friendly and have excellent heating performance, which makes them suitable for electric vehicles. The recirculation mode can save energy but requires a dehumidification function to ensure driving safety. Therefore, this paper proposes a transcritical CO2 desiccant heat pump, which differs from the typical transcritical CO2 heat pump system by incorporating an indoor evaporator and a full-pass throttle valve. The flow area of the full-pass throttle valve can be adjusted to obtain the appropriate dehumidification rate. In addition, this study suggested using the desiccant heat pump coefficient of performance (DHCOP) to evaluate the overall energy efficiency of the heat pump system. We have investigated the dehumidification rate and optimal discharge pressure under different operating conditions. The results show that even under the harsh operating conditions at -10 °C, the HDCOP of the transcritical CO2 desiccant heat pump can still exceed 2.1, and reach 3.12 at a moderate condition of Ta=5 °C. The transcritical CO2 heat pump desiccant system demonstrates significant energy-saving potential.