Conversion of a direct to an indirect commercial (HFC134a/CO2) cascade refrigeration system: Energy impact analysis

Energy impact of conversion of a direct HFC134a/CO₂ cascade refrigeration system to an indirect HFC134a-secondary fluid / CO₂ cascade for commercial applications is experimentally analysed. Refrigeration systems, fully described, have been tested in laboratory conditions, at three condensing temperatures (25, 35 and 45 °C), providing the cooling needs to a cabinet for fresh product (2 °C) and to another for frozen product (?20 °C), both placed inside a climatic chamber simulating the indoor conditions of a supermarket. Energy evaluation considered 24 hour tests of stable operation in each test condition. A decrease from 1.9 to 3.5 K of the evaporation temperature of the high temperature cycle has been measured when using an indirect system. It resulted in a variation of the energy consumption of the whole system between 7.6 to 14.0% when using propylene-glycol/water and between ?0.3 to 11.1% when using Temper ?20^® as secondary fluid.