The refrigerants used to cool the heat generated in semiconductor production are Freons, which are now subject to regulation because of their high ozone depletion potential (ODP) and global warming potential (GWP). Therefore, R-744 is considered an eco-friendly refrigerant. This study experimentally analyzed the effect of the refrigerant charge amount based on the temperature discharged after cooling objects when operating a brine chiller using R-744 under subcritical conditions. The results showed that the optimal charge amount in terms of the coefficients of performance (COP) differed from that in terms of the maximum cooling capacity. In case of the apparatus used in this study, the optimal refrigerant charge amount with maximum cooling capacity was estimated at 8.2 kg when the temperature of the cooling object was in the range of −20 °C and −10 °C and at 9.2 kg when the temperature of the cooling object was 0 °C. However, in terms of COP, the optimal refrigerant charge amount was estimated at 8.2 kg when the temperature of the cooling object was in the range of −20 °C and 0 °C. This difference was attributed to the variation in the required evaporation heat capacity with the target temperature of the cooling object.
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