Performance Analysis of CO₂ Heat Pump System Based on Ejector and Integrated Mechanical Subcooling

To reduce greenhouse gas emissions and improve the performance of space heating systems, a transcritical CO₂ heat-pump heating system using an ejector and integrated mechanical subcooling (EJ-IMS) is proposed. A thermodynamic model of the system is developed with the coefficient of performance (COP) as the objective function, and the subcooling degree and discharge pressure are optimized. The winter heating performance of the system located in cities located in different climate zones was evaluated. The results show that the EJ-IMS system has a maximum COP, corresponding to the optimum subcooling degree and the optimum discharge pressure. The optimum subcooling degree is 26.44%-39.21% lower than that of the integrated mechanical subcooling system, and the optimum discharge pressure of the EJ-IMS system is 0.27%-9.37% lower than that of the baseline system and ejector system. The COP and exergetic efficiency of the EJ-IMS system are 6.09%-37.74% and 6.75%-46.02% higher than those of the three conventional systems, respectively. The heating seasonal performance factor of the EJ-IMS system is 6.89%-29.61% higher than those of the three systems, indicating that the EJ-IMS system is suitable in cold regions. This study provides a theoretical reference for the construction of efficient CO₂ space-heating systems.