Energy, Exergy, and Environmental (3E) analysis of transcritical CO2 refrigeration cycle with an expander, an internal heat exchanger, and a mechanical sub-cooler

The present study investigates energy, exergy, and environmental performances of the transcritical CO 2 refrigeration cycle. In this study, a mathematical model is developed in MATLAB and interfaced with REFPROP to call refrigerant properties. The cycle is studied with various configurations using an internal heat exchanger, expander, and mechanical sub-cooler. A parametric study is conducted to examine the effects of gas cooler pressure, evaporator temperature, and gas cooler exit temperature on the COP and exergy efficiency of the systems, with comparisons made to the basic cycle. The study resulted in the finding that the cycle with an expander achieves the highest COP of 3.21 with 32.83% increase over the basic cycle and an exergy efficiency of 22.7% under their respective optimal gas cooler pressure. The IHX cycle suffers the maximum exergy destruction, in which the gas cooler of the cycle has the maximum irreversibility. In addition, the TEWI analysis was also performed, and the study showed that the expander cycle reduced 23.74% annual CO 2 emissions, compared to the basic cycle under their respective optimal gas cooler pressure, as the energy recovered from the expander has been used to reduce the compressor power. Moreover, Correlations for the optimal heat-rejection pressure have been developed for each configuration, which avoids repeated simulations/experiments to predict the optimal pressure of the specific cycle, assisting the researchers in system performance optimization and system design.