Master's Thesis Dennis Körner

 

In order to enlarge market penetration of technologies for the use of sustainable energy sources, it is necessary to increase efficiency and reduce CO2-emissions in comparison to the combustion of fossil fuels. In the context of domestic heat generation applications, these development goals are of great importance.

Compression heat pumps are sustainable alternatives to the combustion of fossil energy sources for the heat supply. However, the refrigerants in compression heat pumps have a high global warming potential. Therefore, the European Union has passed a law in regulation (EU) No 517/2014 that will limit the sale of high global warming potential refrigerants in the near future. Consequently, the use of these refrigerants will be uneconomical and appropriate alternatives have to be found.

Both, the large number of available refrigerants, as well as the requirements regarding thermodynamic properties, safety as well as control and efficiency of the system imply a multi-dimensional optimization problem with respect to the selection of refrigerants. For these reasons, the design of heat pumps requires amodel-based development to reduce development costs.

Hence, the aim of the present master’s thesis is the development of a dynamic heat pump simulation model. In order to enable the transfer of the application to other systems with little effort, the modeling is done on the basis of component level. The thermodynamic cycle is represented by four states. This yields a small number of model parameters that are decisive for the effort of model calibration. Decisive parameters in the modeling of a heat pump are isentropic efficiency ´is and volumetric efficiency ¸l of the compressor. The determination of the two unknown parameters requires the development of a corresponding method. A following comparison with literature confirms the plausibility of the results.

The model development and determination of the parameters result in a plausiblemodel obtaining a maximumrelative deviation of 1.5%in terms of heat capacity and COP compared to experimental data. As part of the reflections, the model is suitable for representation of the operating behaviour at different source temperatures and use temperatures. According to validation, the model is used to investigate different operating strategies of heat pumps. Focussing on the condition of the refrigerant at the outlet of the evaporator its influence on the heat capacity as well as the COP of the heat pump is investigated. The maximum heat capacity results from the refrigerant being completely evaporated. Thus, compared to the superheating of 1K to protect the compressor, an increase of 5%in the heat capacity and the COP can be achieved. Partial evaporation of the refrigerant is not appropriate.