Tailor-made heat pump systems generally employ application-specific refrigerant mixtures, alongside a customized compressor and component configuration, optimized for the highest possible COP. However, such individualized systems come with significant challenges like high investment costs, unique designs, long planning and manufacturing times etc. To accelerate the transformation of heat generation, the use of conventional, commercially available components and standardized configurations may offer a practical solution. A single refrigerant mixture suitable for a broad range of source and sink temperatures and temperature spreads, combined with an optimized balance between investment costs and operating costs.
The initial theoretical study on zeotropic refrigerant mixtures and the accompanying conceptual design for the experimental setup were introduced at the Herrick Conference in 2024. The subsequent experimental findings will be presented in this study. Propane and butane and their mixtures at various concentrations have been tested. Variations in temperatures (source 30 °C…50 °C, sink 55 °C…85 °C), temperature spreads (10…20K), and compressor types have been analyzed. The system's coefficient of performance (COP), the isentropic efficiency of the compressors and exergy losses in each cycle components are analyzed for different boundary conditions. The experimental results demonstrate that zeotropic mixtures can outperform pure fluids. This paper presents the results obtained from an optimized simulation model developed in Modelica/Dymola using the TIL library and was fitted to the latest experimental data. Within defined boundaries, this model is capable of identifying ideal mixture compositions and predict performance across different operating points.