Energy recovery by means of a radial piston expander in a CO2 refrigeration system

Natural refrigeration fluids as CO2 represent a very promising alternative to hydrofluorocarbons (HFCs) but they generally entail lower COP values. The possibility of recovering the large throttling losses by using an expander could give a substantial contribution to the performance improvement. In this work, a reciprocating expander developed from a hydraulic motor was experimentally analyzed. Despite of the mechanical losses due to the different original application of the machine, the thermodynamic cycles showed very promising results with the adoption of this solution. The machine isentropic efficiency was 19%, while the indicated efficiency was 66%, showing a very interesting potential of the expander. Thus, by considering a reasonable value of mechanical efficiency about 65%, the isentropic efficiency would be around 40%. Consequently, the entailed COP potential improvement, compared to a refrigeration system with simple throttling valve is currently at 7.4%, while it might overcome 20%.