Energy performance and environmental assessment of a commercial ULT freezer retrofitted with low-GWP refrigerants and electronicexpansion valves.

Operational challenges faced by ultra-low temperature (ULT) systems have led to their exclusion from environmental policies, resulting in insufficient market development. Consequently, currently used refrigerants have a high global warming potential (GWP), and technologies remain highly inefficient. Hence, this article experimentally analyses the operation of a commercial two-stage cascade ULT freezer retrofitted with A1 low-GWP refrigerants and electronic expansion valves. R448A is proposed for the high-temperature stage (HTS), and R469A, R472B, and R473A are proposed for the low-temperature stage (LTS) to replace the baseline refrigerants R404A (HTS) and R23 (LTS). Furthermore, the use of electronic expansion valves is compared to that of capillary tubes. The investigation initially focuses on the pull-down operation, in which the temperature varies from 20 ◦C down to -70 ◦C. After that, the hysteresis operation with freezer temperatures of -70 ◦C, -60 ◦C, and -50 ◦C is studied. The pull-down time of alternative refrigerants is higher than the baseline due to a reduced cooling power at the lowest temperatures. Regarding the hysteresis operation, the highest coefficient of performance (COP) is achieved by the R448A/R472B and R448A/R469A refrigerant pairs, which are up to 22.14% and 17.09% higher than the R404A/R23 pair, respectively. Moreover, R448A/R473A exhibits the highest cooling power, up to 73.18% higher than R404A/R23. Finally, the carbon footprint analysis reveals that all the proposed refrigerants significantly reduce (50% to 75%) the equivalent CO₂ emissions compared to the baseline system. Therefore, the solutions proposed in this work enable a reduction in environmental impact while increasing the energy efficiency of ULT systems.