CO 2 has emerged as very good alternative to replace HFC refrigerants with high global warming potential to be use in cascade refrigeration cycles. An experimental study was performed to evaluate the energy performance and environmental impact of the cascade system using R134a, R513A, and R1234yf as refrigerant in the high-temperature cycle and CO 2 in the low-temperature cycle, considering the inclusion of a gas cooler. Tests were performed at condensation temperatures varying from 34 to 43 °C, where the refrigeration capacity ranged from 3.3 to 3.7 kW and evaporator air temperatures was maintained around –18 °C. The experimental results indicate that the introduction of the gas cooler led to reductions of approximately 4.3% in both compressor discharge temperature and power consumption, while the average COP decreased by 2.1%, for an air temperature of −18 °C and a condensing temperature of 43 °C. Related to the total equivalent warming impact (TEWI), when the R134a was replaced by those ones with low-GWP the results indicated substantial reductions. The TEWI was applied for different scenarios, for Brazilian case reductions reached 42.6% and 70.5% with R513A and R1234yf, respectively, whereas for Saudi Arabia the corresponding reductions were 22.5% and 36.8%. Similar behaviors were found for France and USA, mainly influenced by regional electricity emission factors. Overall, these results states that R513A and R1234yf can be an effective drop-in replacement for the R134a, and by the introduction of the gas cooler it can promote the system sustainability by reducing direct and indirect emissions, maintaining the cooling capacity.
Ojeda et al. (Sun,) studied this question.