Energy and exergy analysis on hydrofluoroolefin/ hydrofluorocarbon (HFO/HFC) refrigerant mixtures in low and medium temperature small-scale refrigeration systems

The new refrigerants such as HFO-1234yf and HFO-1234ze have been considered as long-term replacements for HFC-134a to comply with the Kyoto protocol. In small size refrigeration systems, these refrigerants have poor performance than HFC-134a besides their minor flammability. Previous studies reveal that the addition of HFC-134a in small quantity can improve the performance of a system without exceeding the global warming potential limit (150) prescribed by the European Union. However, this concept is not studied in small-scale refrigerators. Therefore, the performance of low and medium temperature systems of capacity 190 and 285 litre, respectively, working with different hydrofluoroolefin/ hydrofluorocarbon (HFO/HFC) mixtures, has been studied by mathematical simulation. The software tool 'MATLab' and the refrigerant property database 'REFPROP' have been used in the simulation. The results showed that the coefficient of performance (COP) of Hydrofluoroolefin (HFO) refrigerants and its mixtures decreases from 2.4 to 15.7% than that of HFC-134a. Among the mixtures, HFO-1234ze/HFC-134a (90/10) shows better performance and its predicted coefficient of performance (COP) and exergetic efficiency are 4-8.3% and 5.1-10.5%, respectively, higher than that of other mixtures considered in this study.