Conference article

Heat pump technology provides an efficient and sustainable solution for both heating and cooling. A traditional heat pump can be defined as a mechanical-compression cycle refrigeration system powered by electricity. Traditional refrigerants used in heat pumps are ammonia or chlorinated and fluorinated hydrocarbons. Because many of these chlorofluorohydrocarbons (CFC’s) are ozone-depleting components, evaluation of more environmentally friendly refrigerants like pure hydrocarbons is important. The efficiency of a heat pump is traditionally measured by the ratio of delivered heat at a high temperature divided by the electricity (or work) input. This is defined as the coefficient of performance (COP). There are several simulation tools available for the simulation of heat pumps. Traditional process simulation tools like Aspen HYSYS or Aspen Plus are useful because they have data for several components inside the program, and many thermodynamic models like equations of states available. It is of interest to calculate the efficiency of a heat pump system when varying temperature conditions, refrigerants, simulation programs and thermodynamic models. There are few references to such comparisons in the open literature. The circulation medium (refrigerant) alternates by the help of a compressor and an expansion valve between the temperatures 22 and 7, 24 and 5 or 24 and -15 °C. The lowest temperature is the evaporation temperature and the highest is the condensing temperature. The pressures were specified as the saturation pressures at the given temperatures. The evaluated components are ammonia, R-11, R-12, R-22 and propane. The equations of state Peng-Robinson and Soave-Redlich-Kwong (SRK) and the activity model Non-Random-Two-Liquid (NRTL) were used in the process simulation programs Aspen HYSYS and Aspen Plus. COP values have been calculated to values between 3 and 9. The highest COP was calculated for the lowest temperature difference. The components giving the highest COP value between the temperatures 22 and 7 °C were ammonia and R-12, and R-22 gave the highest COP between -15 to 22 °C. Propane (which is not a CFC) gave slightly lower COP values than the other components. The differences between the thermodynamic models and the different programs were normally low. However, some differences between Aspen Plus and Aspen HYSYS for the same model were calculated. The calculated deviations between the same models using different programs are difficult to explain. Different model parameters in different programs may explain differences between the same models in different programs. Aspen Plus and Aspen HYSYS are evaluated to be powerful tools for heat pump calculations. The calculated differences between heat pump efficiencies with different components at different conditions are thought to be reasonable.

heat pump; Aspen HYSYS; Aspen Plus; refrigerant; COP

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