Numerical Study and Experimental Comparison of CO2 Reciprocating Compressors for Small Cooling and/or Freezing Capacity Applications

The present paper is a numerical and experimental comparative study of hermetic and semi-hermetic reciprocating compressors working with carbon dioxide as fluid refrigerant against the conventional R134a hermetic compressors. When cooling conditions for one-stage compressor type (i.e., evaporation temperatures between 7.2oC and –10oC) have been considered, the numerical and experimental results obtained have shown a reasonable good agreement, while the comparative global values have indicated very similar efficiencies between the carbon dioxide compressor and the conventional ones. In all these cases the CO2 semi-hermetic compressor presents higher mass flow rate and better efficiency than the CO2 hermetic compressor. However, when freezing conditions are analysed (i.e., evaporation temperature between –10oC and –40oC) the onestage CO2 compressor shows lower COPs in comparison with R134a conventional compressor. In these cases a numerical study of the availability of two-stage semi-hermetic reciprocating compressors is presented in order to obtain comparative or even better efficiencies against conventional hermetic reciprocating compressors.