Thermodynamic Evaluation of Low-GWP A1 Refrigerants for Ultra-Low Temperature Refrigeration Applications

Slow market development has caused the lack of low-GWP A1 refrigerants for ultra-low temperature (ULT) refrigeration. Consequently, the high-GWP refrigerant R23 (GWP = 14,600) remains widely used within the ULT sector. For this reason, this paper proposes a comprehensive thermodynamic analysis of recently developed CO2-based mixtures as low-GWP A1 alternatives to R23 for ULT applications, R469A (GWP = 1357), R472B (GWP = 526), R472A (GWP = 353), and R473A (GWP = 1830). In addition, three system configurations are analysed, the basic two-stage cascade system, and configurations incorporating internal heat exchangers (IHXs). Keeping a constant high-temperature stage (HTS) condensation temperature at 35 °C, three low-temperature stage (LTS) evaporation temperatures are considered, −70, −60, and −50 °C. The highest coefficient of performance (COP) is reached by R23 across all operating conditions and configurations. Among the alternative refrigerants, R473A exhibits the highest COP (0.74% to 1.26% lower than R23). The implementation of IHX results in a reduced COP compared to the basic cycle. R472B is the refrigerant least negatively affected by the IHX implementation due to its high glide. Finally, the environmental impact of R23 is notably reduced by all the alternative refrigerants (up to 95%). This paper’s findings highlight the potential of alternative refrigerants as replacements for R23 in ULT applications.