Amongst alternative energy sources, geothermal energy is well known for centuries. Especially in the near and far district heating application, geothermal heat is utilized as an addition or rather an alternative to the heat extraction from caloric power plants. In this particular field of application geothermal facilities have advantages like low emissions due to closed thermal water circuits, small footprints during operation and a continuous supply of thermal energy. Since geothermal water composition is highly dependent on local geological conditions, also the operating parameters of the corresponding geothermal facilities vary between different locations. First and foremost is the heat transfer rate, which highly depends on local occurring gas contents, ion concentrations, paraffins and various solids found in geothermal fluids. This thesis focuses specifically on those fluid portions that primarily affect heat transfer. The basis of these fluid portions is established by measurement and analysis data from Austrian and German geothermal wells. Due to the present legislative but also technical and safety relevant circumstances, a strict separation between geothermal water and process circuits or heating grids is mandatory in Germany. Based on technical and economic aspects this separation is implemented by the use of plate heat exchangers. In order to perform a realistic heat transfer design of these heat exchangers there is currently a lack of publicly available fluid data as well as calculation models. It is therefore the aim of this thesis to determine essential geothermal water components and their related impact on heat transfer. For the calculation of this influence a two-phase fluid model is applied, that utilizes operating parameter ranges of an operational geothermal facility. Evaluation of the calculation results show distinct tendencies, that with increasing salinity the heat transfer is reduced. The negative impact on heat transfer due to free gas appears to be decreased by its enhancement on fluid dynamic properties.