Secondary refrigerant systems require a pump to circulate the coolant around the supermarket and there is an extra heat exchanger temperature drop. The extra condensing heat exchanger requires a temperature difference to drive the heat transfer and so the MT evaporating temperature must be lower than the secondary CO2 temperature. However, the better heat transfer properties of CO2 in the cabinets allows the circulating fluid to operate at 30.2°F instead of 26.6°F with glycol. In this model a temperature difference of 9°F has been applied so that the MT evaporating temperature is 21.2°F
Valves, Controls and System Protectors for R-744
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