Thermodynamic performance and CO2 emission analysis of transcritical CO2 two-stage compression refrigeration system with intermediate gas supplementation

Low evaporation temperature characteristic of transcritical CO2 refrigeration systems results in high discharge temperature and decreased system efficiency. In this paper, a transcritical CO2 two-stage compression refrigeration system with intermediate gas supplementation (TCTCRS-IGS) was proposed, and thermodynamic and CO2 emission analysis was conducted. Firstly, the transcritical CO2 two-stage compression refrigeration system (TCTCRS) with and without intermediate gas supplementation was compared. Then, experimental investigations were conducted to analyze the effects of evaporation temperature, high pressure, intermediate pressure, gas cooler outlet temperature, and intermediate cooler outlet temperature. Besides, CO2 emission was analyzed at different conditions. The results show that the TCTCRS-IGS system achieved a 24.73 % reduction in discharge temperature and a 7.42 % increase in COP compared to TCTCRS. Meanwhile, the TCTCRS-IGS system is less affected by the intermediate cooler outlet temperature. However, it is significantly influenced by the other parameters. As the evaporation temperature rises, the cooling capacity and COP improve by 57.7 % and 23.9 %, respectively. The COP shows an initial increase followed by a decrease with high pressure, reaching a maximum value of 1.39. The COP reaches its highest point of 1.5 at an intermediate pressure of 4.2 MPa. As the gas cooler outlet temperature increases, COP initially decrease and then rise. Besides, the CO2 emissions are influenced by evaporation temperature, high pressure, and gas cooler outlet temperature, with little impact from intermediate pressure and cooler outlet temperature. The TCTCRS-IGS system offers economic costs through superior energy efficiency, lowering operating and environmental costs. The TCTCRS-IGS system contributes to the enhancement of the TCTCRS performance, fostering the development of low-carbon technology.