Research on the performance of ultra-low temperature cascade refrigeration system based on low GWP refrigerants

The EU Security Council and Parliament have tentatively agreed to ban fluorinated gases with a global warming potential (GWP) higher than 150 in split air conditioners and heat pumps from 2027. This will further motivate the refrigeration industry to accelerate the search for refrigerants with low GWP and zero ozone depletion potential (ODP). At present, research into low GWP refrigerants for cascade systems is limited, focusing mainly on single refrigerant substitutes without comprehensive comparisons and lax GWP restrictions. In this study, the cascade refrigeration cycle (CRS) system is established to meet the demand of -100 to -50 degrees C. The GWP of the refrigerants is strictly controlled below 150, and a comprehensive screening of the four generations of refrigerants is carried out to identify refrigerant pairs that meet environmental and refrigeration requirements. The relationship between the high-temperature cycle (HTC) evaporation temperature and the optimal coefficient of performance (COP) is determined, and the effects of the low-temperature cycle (LTC) evaporation temperature T-e concerning with mass flow rate, discharge temperature of compressor, compressor power consumption, exergy destruction, and exergy efficiency are analyzed in detail. The thermodynamically superior refrigerant pairs are identified by comparison with several conventional refrigerant pairs. The results show that when T-e > -67 degrees C, R170/R600a is preferred, and when T-e <= -67 degrees C, R170/R1270 is preferred. In the temperature range of -100 similar to -50 degrees C, R170/R1270 is the better refrigerant pair, which can improve the performance by 6.39-13.11 % than traditional refrigerant pairs. Finally, the exergy destruction analysis of CRS components is carried out, which provides a reference for refrigerant selection and system optimization of CRS in the field of ULT.