Comprehensive assessment of a novel CO2 ejector-integrated dual-temperature evaporation cycle for dual-mode operation

CO 2 , an environmentally friendly refrigerant, has significant potential for heat pump applications. Introducing ejectors can enhance CO 2 cycle performance, but their unidirectional flow characteristics pose challenges for switching between cooling and heating modes. This paper proposes a dual-mode dual-temperature evaporation ejector expansion cycle (DEEC). By integrating a four-way valve and two six-way valves, the DEEC operates as a dual-temperature ejector expansion cycle in both cooling and heating modes, leveraging the synergistic advantages of the ejector and dual-temperature evaporation, thereby reducing compressor pressure ratio, throttling losses, and heat transfer irreversibility. To evaluate its performance, the DEEC is compared with the basic vapor compression cycle (BVCC) and single-temperature ejector expansion cycle (SEEC) using thermodynamic, environmental, and economic models. Under rated conditions, the calculated coefficient of performance (COP) improvements of DEEC over BVCC are 25.9% and 14% in cooling and heating modes, respectively, with corresponding exergy efficiency gains of 21% and 15.5%. Calculated COP gains over SEEC are 7.3% and 4.3%, with exergy efficiency gains of 6.1% and 4.8%. Additionally, the annual performance factor improvements over BVCC and SEEC are 14.9%–17.7% and 4.3%–5.4%, respectively, across the evaluated cities. Environmental analysis indicates carbon emissions are reduced by 13%–15% and 4.1%–5% compared to BVCC and SEEC, respectively. Under the reference electricity price, the estimated payback periods range from 0.6 to 4.2 years in the selected cities except Haikou, where the annual load is relatively low. Overall, the DEEC demonstrates notable advantages for year-round cooling and heating applications in buildings and transportation.