An experimental analysis of a supermarket plant working with carbon dioxide as refrigerant

This paper presents the experimental results of a commercial refrigeration plant for supermarkets working with R744. The system was installed for testing purpose in a test area, simulating a 300 m2 supermarket. The system has a total capacity of 31 kW in medium temperature (MT - evaporation temperature -10°C) and about 15 kW in low temperature (LT - evaporation temperature -35°C). The swept volume of the compressors is 5.4 m3/h for MT and 5.9 m3/h for LT, the MT and the LT circuits are completely separated. The MT unit has two single stage compressors in parallel, while the LT unit has two compressors in parallel of two-stage internal compound type. In both LT and MT units on the high pressure side, the heat is rejected to water. The throttling system includes a differential valve or a step-motor electronic valve (acting as a controlled back-pressure valve) in alternative, coupled with a liquid receiver and thermostatic electronic valves as the final stage. The experimental tests were run, both in subcritical and transcritical conditions, using the two valves varying the gas-cooler water inlet temperature from 15 to 35 °C. Different setting of the differential valve spring were used.