Comparative 4E and advanced exergy analyses and multi-objective optimization of refrigeration cycles with a heat recovery system

Abstract

This paper compares the refrigeration cycle (RC) and the heat recovery refrigeration cycle (HRRC) with ejector from the 4E (energy, exergy, exergoeconomic, and exergoenvironmental) and advanced exergy point of view. In HRRC, heat recovery is used as a heat source for an organic Rankine cycle. Two working fluids R744 (CO2) and R744A (N2O) have been selected. The performance of the two cycles has been compared with both working fluids. The results of the energy and exergy analysis show that using HRRC with both refrigerants increases the coefficient of performance (COP) and exergy efficiency. COP and exergy efficiency for HRRC-R744 have been obtained 2.82 and 30.7%, respectively. Due to the better thermodynamic performance of HRRC, other analyses have been performed on this cycle. Exergoeconomic analysis results show that using R744A leads to an increase in the total product cost. Total product cost with R744 and R744A have been calculated by 1.56 $/h and 1.96$/h. Moreover, exergoenvironmental analysis showed that using R744A refrigerant increases the product environmental impact by 32%. Due to the high amount of endogenous exergy destruction rate in the compressor and ejector compared to other equipment, they have more priority for improvement. Multi-objective optimization has been performed with exergy efficiency and total product cost objective functions as well as COP and product environmental impact for both refrigerants, which results indicate that HRRC-R744 performs better economically and environmentally. In optimal condition, the value of exergy efficiency, total product cost, COP, and the product environmental impact have been accounted for by 28.51%, 1.44 $/h, 2.76, and 149.01 mpts/h, respectively.