Recent developmnets in commercial refrigeration systems using CO2 as the refrigerant

The aim of this paper is to present some recent developments in a commercial refrigeration system operating with CO 2 as the refrigerant. A real plant, intended to serve a wholesale centre, installed in the late Summer of 2006 year in central Europe, is described. The system includes both low temperature and medium temperature units and it is operated according to a transcritical or subcritical cycle depending on the external air temperature. Electronic expansion valves control the upper cycle pressure both during transcritical and subcritical operations. The low temperature units run a double stage compression and double throttling cycle with removal of the flash gas from the intermediate pressure receiver and inter-stage cooling. The gas coolers have been provided with a water spray system, which assures a significant benefit during summer operations. A rather limited sample of measurements of operational variables is here presented and the data collection is in progress to provide a full account of the system operation throughout the entire year.