Combined effect of refrigerant amount reduction and composition change on heat pump system performance during refrigerant mixture leakage

The natural refrigerants and hydrofluoroolefins (HFOs), which are proposed as alternatives to traditional refrigerants, have weaknesses in terms of flammability, cost, or system performance. As a solution, refrigerant mixtures offer the advantage of variable thermodynamic properties, but their main drawback is the composition change caused by the refrigerant leakage. This study analyzes the performance change during the leakage process, considering the combined effect of refrigerant amount reduction and composition shift. A mixture of R32/R1234yf with an initial composition of 20/80 wt% was utilized as a working fluid, and four leakage scenarios were employed: a vapor or liquid leak occurring during winter at -10 degrees C or summer at 30 degrees C. The composition change during the leakage was calculated by the simulation model, and then experiments were conducted to measure the performance with the calculated composition. The simulation results show that the vapor leak in winter leads to the most significant composition change of 7.8%p, when 57.1% of the initial charge escapes from the system. From the experimental results, the coefficient of performance (COP) exhibits the lowest value after the liquid leak in summer due to the increased mass fraction of R32, with a decrease of 89.5% compared to the initial COP. This degradation consists of 80.2%p due to refrigerant amount reduction and 9.3%p due to the composition shift. By considering the effects of both refrigerant amount and composition, this study provides a comprehensive analysis of the performance changes in a heat pump system during refrigerant mixture leakage.