Influence of the superheat associated to a semihermetic compressor of a transcritical CO2 refrigeration plant

This work evaluates, from an energetic point of view, the effects of the superheat caused in the refrigerant by the electric motor cooling (SHSC) in a semihermetic compressor installed in an experimental refrigerating plant, which operates with CO2 as the working fluid in transcritical conditions. The analysis is based on 84 experimental tests which cover a wide range of operating conditions of the plant: three evaporating levels (0, −10, −17 °C) at four compressor speeds (1150, 1300, 1450, 1600 rpm) over a range of discharge pressures from 74.2 to 104.9 bar.The paper presents the empirical model of the compressor and its validation with the experimental measurements, which allows the behaviour of the facility to be calculated with prediction errors below 5%. With the model, the effect of the SHSC on the energy efficiency of the plant is evaluated by comparing the actual performance of the facility with the simulated behaviour of the plant without considering the SHSC produced by the semihermetic compressor. The maximum estimated reductions, due to the SHSC of the compressor, are a 20% in cooling capacity and a 23% in COP.