Performance analysis of a double-efficient CO2 cooling and heating system using an ejector

Abstract

This paper presents a double-efficient CO2 cooling and heating system using an ejector, which can operate as modified dual-evaporators ejector expansion cycle (MDEEC) in cooling mode or as conventional heat pump cycle (CHPC) in heating mode through the reasonable arrangement of valves, and countercurrent heat transfer of CO2 with cooled or heated air is achieved in both modes. An ejector is utilized to recover the expansion work and two evaporators provide independent air dry-cooling and dehumidification in cooling mode. Two thermodynamic models are developed to investigate the effects of various parameters on the cycle performance. Comparison of proposed cycles with ejector expansion refrigeration cycle (EERC) and conventional dual-evaporator vapor compression cycle (CDVCC) are conducted based on energy analysis. The results show that coefficient of performance (COP) of this system is improved by more than 25% compared to EERC, and 33.62–56.27% compared to CDVCC. Besides, performance comparison of CHPC using CO2 and R134a is conducted, which reveals that COP of CO2 cycle is consistently higher, maintained above 2.7, and the maximum value is 5.36. The COP improvement is up to 29.74%, and the minimum value is 5.37%. This study provides a solution for efficient cooling and heating applying CO2 as refrigerant.