A modified dual-ejector enhanced dual-evaporator transcritical CO₂ refrigeration cycle: 4E (Energy, Exergy, economic and Environmental) assessment

Recently, the transcritical CO₂ refrigeration cycle shows advantages in supermarket refrigeration applications. However, there is high expansion work recovery potential due to its large pressure difference between the inlet and outlet of the expansion valve. Therefore, a dual-ejector enhanced dual-evaporator transcritical CO₂ refrigeration cycle (DECRC) is presented in this paper to recover expansion work by using ejectors. The thermodynamic models based on the energy, exergy, economic and environmental analysis are developed to compare their performance with the basic transcritical CO₂ refrigeration cycle (BCRC) and the ejector-enhanced transcritical CO₂ refrigeration cycle (ECRC). The energy analysis results indicate that compared with the BCRC and ECRC, the cooling coefficient of performance (COP_c) of DECRC improves by 49.7% and 27.2%, respectively. The exergy analysis results show that the exergy destruction of the expansion valves in BCRC, ECRC and DECRC is 22.6%, 14.2% and 0.8%, respectively, which demonstrates that the introduction of the ejector could effectively reduce the exergy destruction of the cycle. The economic analysis results reveal that the cost per unit of exergy production by DECRC is 33.2% and 21.5% lower than that of BCRC and ECRC, respectively, while the impact of using ejectors on the total cost of the system is small 16.1%. The environmental analysis demonstrates that the carbon emission of DECRC is 33.2% and 21.4% lower than that of the BCRC and ECRC, respectively, under the given condition. Furthermore, the DECRC could obtain higher performance improvement when the ambient temperature is higher or the evaporating temperature is lower, indicating that the DECRC has a promising application in supermarket refrigeration.