Numerical investigation on the heating performance of a transcritical CO2 vapor-injection heat pump system

CO2 is a new type of friendly refrigerant. In order to investigate the effect of the operating parameters of the transcritical CO2 heat pump system on heating performance, the transcritical CO2 vapor-injection heat pump (VIHP) system simulation models were developed. The models were validated with the previous experimental results. All the deviations are within the acceptable range. The simulation results show that the heating capacity will meet the requirement of electric vehicle (EV) in the cold region when compressor revolving speed is greater than 4000 r min(-1). The heating capacity of the VIHP system is greater than that of the transcritical CO2 single-stage heat pump (SSHP) system; besides, the coefficient of performance (COP) of VIHP system is 30.7-38.6% greater than that in SSHP system under the same condition. The VIHP system is more suitable for EV to run in the cold region. The COP reaches a peak at a certain injection pressure. The correlation of optimization injection pressure is developed. Therefore, the simulation data provide great guidance for designing a transcritical CO2 heat pump system and developing the controlling system of the heat pump system.