Experimental evaluation of a two-stage cascade ultra-low temperature refrigeration system with internal heat exchanger using hydrocarbon pair R290/R170 and comparison with HFC baseline

• Comparison between natural refrigerants R290/R170 and traditional refrigerants R404A/R23. • The R290/R170 pair achieved the best COP (0.95) and energy efficiency among the refrigerants tested. • Switching from R404A/R23 to R290/R170 reduces CO 2e emissions by 50 %. • R448A/R170 shows intermediate energy efficiency, but closer to R404A/R23. • R290/R170 generates lower discharge temperatures, protecting the compressor. Traditional vapor-compression systems face significant operational challenges below −50 °C, at ultra-low temperatures, and are currently excluded from F-gas Regulation. Also, there is a lack of experimental studies in the field, which has caused the currently used systems to be highly inefficient and use greenhouse gases as refrigerants, such as R23. For this reason, this article experimentally analyzes a two-stage cascade vapor compression cycle with internal heat exchangers operating at ultra-low evaporation temperatures (−50 °C and −60 °C). The natural refrigerant pair based on hydrocarbons R290/R170 (high and low-temperature stage, respectively) is compared with the refrigerant pair based on hydrofluorocarbons R404A/R23, traditionally used in ultra-low temperature refrigeration. The refrigerant pair R448A/R170 has been tested as a transitional alternative during the refrigerant replacement. A custom-designed flexible experimental test bench was constructed to measure each refrigerant pair’s operation. The main operational parameters in steady-state tests have been measured at the condensation temperatures of 25 °C, 28 °C, and 31 °C and evaporation temperatures of −50 °C and −60 °C. The experimental results show that the refrigerant pair R290/R170 offered the highest COP (0.95), compressor volumetric efficiency, and lowest discharge temperature. The refrigerant pair R448A/R170 offered an intermediate energy performance, but much closer to the refrigerant pair R404A/R23 than R290/R170. Due to its higher energy efficiency and lower global warming potential, a total equivalent warming impact analysis quantified the CO 2 equivalent emission reduction by 50 % when changing from R404A/R23 to R290/R170. Consequently, natural refrigerants must be prioritized as the study demonstrates that they are the best option from a comprehensive analysis.