Compressor model for CO2-doped blends. Correction factor of EN 12900 for mixtures with R152a, R290, R1233zd(E)

Abstract

It has been experimentally verified that doping CO2 with small amounts of other fluids enhances the COP of refrigeration systems thanks to the modification of the thermophysical properties, as it increases the critical temperature and pressure, and moves the operation to subcritical at high ambient temperatures. Up to now, theoretical studies are mainly based on the compressor information provided by the manufacturer according to the standard EN 12900 which represent the behaviour of the compressor using polynomial relations. However, manufacturers only offer information for pure-CO2 compressor operation and there are no tools to predict their performance when working with CO2-doped fluids. This work fills this gap since it develops a correlation for predicting the performance of CO2 compressors when used with mixtures. A CO2 semi-hermetic compressor was tested with mixtures (R152a at 5 and 10 %; R290 at 5 %; and R1233zd(E) at 5 % by mass) and the data was used to define a correction factor of the standard EN 12900 (for pure CO2) to predict compressor power consumption and mass flow rate when working with mixtures. In addition, the model also allows determination of compressor’s discharge temperature, volumetric and overall efficiencies. The model, developed ensuring good balance between complexity and accuracy, allows determination of these variables with a precision of 5 % using as input variables the reduced discharge and suction pressures and the reduced suction temperature. This model can be used to extend the investigation of CO2-doped fluids in more complex refrigeration architectures.