Performance Analysis of Ejector Subcooling Transcritical CO₂ Heat Pump System Driven by the Discharge Waste Heat

To resolve the issues of significant throttling loss and performance degradation of a baseline transcritical CO₂ air-source heat pump system (Base) for building space heating, an ejector subcooling transcritical CO₂ air-source heat pump system (ESH) driven by the waste heat of the compressor discharge gas is proposed in this paper. The thermodynamic performance of the ESH system was optimized and analyzed using four working fluids. Five typical cities were selected for comparison, and the heating season performance factor (HSPF) was analyzed. The results reveal that the coefficient of performance (COP) of the ESH system first increased and then decreased with the increase of discharge pressure, and an optimal discharge pressure exists. Compared with the Base system, the ESH system using R1234ze (Z) displayed the most remarkable improvement in COP (with the highest increase of 20.64%). The discharge pressure of the ESH system reduced by up to 9.20% compared with that of the Base system, and the exergy efficiency increased by 7.13%-18.61%. The HSPF of the ESH system was 9.68% to 14.21% higher than that of the Base system. The performance improvement was higher when it was used in severely cold regions.