Energy and exergy analysis of a transcritical CO2 refrigeration system integrated with vapor injection and mechanical subcooling

Abstract

Mechanical subcooling is an effective method to improve the transcritical CO₂ refrigeration system. To further improve its performance, a transcritical CO₂ refrigeration system is investigated with vapor injection and mechanical subcooling (MVS) using R152a as an auxiliary circulating refrigerant. A comparative analysis with the basic vapor injection CO₂ refrigeration system (BVS) and the mechanical subcooling CO₂ refrigeration system (MSS) is conducted from the perspective of energy and exergy. The results indicate that there are optimal values for the compressor discharge pressure, subcooling degree, and relative intermediate pressure coefficient, which together can maximize the COP of MVS under various operating conditions. At an evaporation temperature of −15 °C and a gas cooler outlet temperature of 40 °C, MVS has a COP of 1.9, which is 17.8 % and 4.9 % higher compared to the BVS and MSS, respectively. The exergy efficiency is increased by 9.5 % and 6.6 %, respectively.