Experimental retrofit of an R404A/R23 ultra-low temperature freezer using R448A and electronic expansion valves

Abstract

The lack of regulations that limit the GWP of refrigerants operating in vapour compression systems with a target temperature below –50°C has caused slower market development. Therefore, limited refrigerants and technologies for ultra-low temperature (ULT) refrigeration have been studied. In this work, an experimental assessment of R448A as a lower-GWP alternative to R404A in the high-temperature stage of a ULT two-stage cascade refrigeration system is done using R23 as the low-temperature stage refrigerant. Furthermore, capillary tubes and electronic expansion valves are compared as expansion devices. First, the pull-down performance starting from three room temperatures (15, 20, and 25°C) down to –80°C is analysed. Then, the hysteresis operation with those ambient temperatures and set freezer temperatures of –80, –70, –60, and –50°C is studied. The pull-down time was higher (38 to 55 min slower) using the capillary tubes compared to the electronic expansion valves. Also, the energy consumption of the hysteresis operation was higher (up to 32.3% higher) using the capillary tubes. The electronic expansion valves obtained comparable energy consumption and cooling capacity with R404A/R23 and R448A/R23. The highest COP is achieved by R448A/R23 (up to 10.2% higher than R404A/R23). Therefore, the suitability of R448A as a replacement for R404A in ULT refrigeration is confirmed.