Reasonable performance comparison for a refrigeration system using different refrigerants: Case with propane and isobutane mixtures with several compositions

•The existing refrigerant comparison methods have limitations.•Performance comparison was conducted in three methods.•To compare the mixed refrigerant, the temperature glide should be considered.•Method that fixed temperature difference of secondary fluid is most reasonable.•The uncertainty of COP measurement in the experimental study was 4.89%. Traditional refrigerants such as HCFC and HFC have a great influence on global warming. On the other hand, natural refrigerants have little impact on the environment, and low global warming potential (GWP) and zero ozone depletion potential (ODP) are key-characteristics of natural refrigerants. Hydrocarbon refrigerant is one of the natural refrigerants with higher COP than other natural refrigerants. Furthermore, performance improvement is promoted by mixing hydrocarbon refrigerants. Due to their characteristics, refrigerant mixtures have an advantageous heat exchange performance over a single refrigerant. Generally, refrigerant mixtures have temperature glide during phase change. Because of this, temperature difference can be maintained uniform during the heat exchange with secondary fluid. In this study, cooling cycle using isobutane/propane mixtures is researched to maximize the performance when changing mixing ratio by simulation. However, refrigerants with different isobutane ratios can be considered completely different refrigerants. Therefore, a good methodology is needed to compare performances of cycle. In this study, unlike previous studies, various methodologies are used to compare the performance of refrigerant mixtures. Also experiments for isobutane/propane mixtures were conducted. Various temperature conditions are used in the simulation study, and outdoor temperature of 35 °C and indoor temperature of 27 °C were used in the experiment to validate the simulation results.