Energy evaluation of drop-in replacements for R134a in cascade CO2/R134a refrigeration units.

The energy performance of CO2 standard booster systems is limited in countries with high ambient temperatures to replace R404A direct expansion architectures. Therefore, cascade refrigeration systems with CO2 in the low-pressure stage can be considered. Most of the conventional cascade refrigeration systems rely on using R134a, a high global warming potential (GWP) refrigerant, in the high pressure stage. However, R134a needs to be replaced by lower GWP refrigerants to meet the targets of current environmental agreements. This study investigates R450A and R513A refrigerants as drop-in replacements to R134a in R134a/CO2 cascade refrigeration units. The experimental energy performance results suggest that both R450A and R513A can substitute R134a in cascade systems. R513A provides comparable COP and cooling capacity values to R134a, whereas the cooling capacity and COP of R450A are lower than that of the baseline R134a.