Bachelor's thesis Bijan Seyed Sadjjadi


Thermal loss modeling of a compressor in dynamic simulations for refrigerant cycles

Schematic thermal losses Copyright: EBC Schematic of the observed thermal losses of a hermetic refrigerant compressor

Aiming for the goal of more efficient heat pump cycles, the compressor as the main consumer of electrical power in refrigerant cycles is observed in this work. A literature review indicated a need for further observations of the compressor heat losses and the impact of the motor heat losses of a hermetic compressor. For this purpose this paper should answer the question, if the thermal losses generated by a compressor in a refrigerant cycle are displayable in physical correct way without the knowledge of the internal dimensions. Further the motor heat losses should be analysed and related to the total compressor heat losses. In order to accomplish that, a reusable Modelica-based simulation model is developed within this work, which is based on a semi-empirical modeling approach. The heat loss phenomena are determined by dividing the compressor in a high temperature and a low temperature part, whereas it is assumed that the motor heat transfer contributed to the compressor shell leads to a evident temperature difference between those parts. Considering the outer compressor shell temperatures as validation parameters for the heat losses and the motor heat losses affecting the compressor shell, first validation results of the compressor simulation model are executed. A RMSE of 2.27 is reached comparing the measured and simulated temperatures in the high temperature part and a RMSE of 1.44 is obtained for the low temperature part. Therefore it can be stated, that the semi-empirical compressor model for variable-speed rotary compressors is capable of presenting reasonable results concerning the heat losses over the compressor shell and the heat losses generated by the compressor motor during the compression process. A nearly linear behaviour between the total shell heat losses and the radiative motor heat losses is obtained within the results. Further observations could deal with an extensive sensitivity analysis pointing on the variables characterizing the refrigerant flow during the compression.