Energy comparison based on experimental results of a cascade refrigeration system pairing R744 with R134a, R1234ze(E) and the natural refrigerants R290, R1270, R600a

Abstract

Refrigeration architectures for low-temperature applications are gaining interest in the Industrial, Commercial and Health fields. One of the most classical architectures is cascade systems, where two mechanical single vapor compression cycles are thermally paired by the cascade heat exchanger (HXcc). The HXcc, acts as condenser for the low temperature cycle and as evaporator for the high temperature cycle. Each cycle is charged with a different refrigerant adapted to the operating conditions. New environmental rules make necessary to find proper refrigerant pairs to get refrigeration plants with high energy efficiency together with environmentally friendly fluids. This experimental work compares the energy performance of a cascade refrigeration system working with the pair R134a/R744 against four alternative refrigerant pairs: R290/R744, R1270/R744, R600a/R744CO2 and R1234ze(E). Laboratory tests were conducted at three heat rejection temperatures: 20, 30 and 40°C, maintaining a fixed low-temperature heat source level (−20°C). The energy analysis shows that R290/R744 and R1270/R744 improve the cooling capacity at low heat sink temperatures, and the pair R290/R744 improves the energy performance at low temperatures. The environmental analysis shows that all the refrigerant pairs achieve a reduction in CO2eq emissions.