Refrigerant selection from an economic and TEWI analysis of cascade refrigeration systems in Europe based on annual weather data

Abstract

Due to environmental concerns and increasingly stringent regulations, refrigerants with low global warming potential must be used in cascade refrigeration systems. However, identifying the most suitable combination of refrigerants is still a major challenge. Therefore, a methodology for selecting refrigerant combinations for cascade refrigeration systems dedicated to freezing applications is presented. A bilevel optimization procedure approach based on a thermodynamic 0D-steady state model and weather data at different locations in Europe (i.e. France, Germany and Spain) has been developed. The system is optimized in terms of the coefficient of performance on an hourly basis as the lower level task and the total annual cost as the upper level task. The results are analyzed with respect to the annual cost and the corresponding Total Equivalent Warming Impact (TEWI). In total, 36 different low GWP refrigerant pairs were studied for a cascade refrigeration system with an imposed cooling load of 100kW. The results of the analysis show that dimethyl ether and R161 have the best performance for the high temperature circuit. However, close performances were obtained with R717 and R152a. For the low temperature circuit, similar results were observed for R41, R170 and R744. For the R161/R744 pair, the optimal annual cost and corresponding TEWI are 141 285€year−1 and 3001t, 108 858€year−1 and 2459t, 105 179€year−1 and 533t for Berlin, Madrid and Paris, respectively. Furthermore, the study shows that the optimal refrigerant selection of the investigated refrigerants is robust for the cooled space temperature and the location of the cascade refrigeration system, as no significant change of the TEWI and the total annual cost ranking of the individual refrigerants is observed.