Analysis for Parameters Affecting Cycle Performance of CO₂ Two-Stage Compression Cycles

The application of CO₂ in air source heat pumps has the advantages of environmentally friendly, non-toxic and harmless, and superior thermal performance, however, it still suffers from the problems of high system pressure and high compressor pressure ratio under large temperature span conditions in cold regions. To address these issues, a CO₂ two-stage throttling intermediate complete cooling dual-compression cycle (TCDC) is adopted to improve cycle performance. Based on this, dynamic simulation modeling of the TCDC has been carried out using the Dymola software. The impact of different parameters, such as the low/high-stage compressor volume ratio (R_v), high pressure (P_H), outlet temperature of gas cooler (T_gs,out) and evaporating temperature (T_L), on the heating performance of the TCDC is analyzed, and the calculation formulas for the optimal low/high-stage compressor volume ratio (R_v,opt) is derived. The results show that the optimal low/high-stage compressor volume ratio (R_v,opt) of the TCDC depends solely on TL and has a significant impact on both the heating coefficient of performance (COP_hot) and heating capacity (Q_hot). Since the impact of R_v on system Q_hot is greater than its impact on COP_hot, the Q_hot demand can be prioritized by adjusting R_v, laying the foundation for a heat priority control strategy.