Simulation of leakage of mildly flammable refrigerants.

The use of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) has been widely restricted. They have been replaced with hydrofluorocarbons (HFCs) in order to protect the ozone layer. However, the leakage of refrigerant into the air from active or end-of-life air conditioners is a serious environmental issue owing to the high global warming potential (GWP) of HFCs. Therefore, replacing HFCs with low-GWP refrigerants has been recognized as a reasonable solution to the problem. In Japan, low-GWP refrigerants such as R1234yf, R1234ze, and R32 have been considered as alternatives to conventional HFC refrigerants. However, these low-GWP refrigerants are often flammable. When refrigerants leak into a space, they tend to accumulate above the floor if they are heavier than air. The refrigerant may ignite if the refrigerant concentration is higher than the low flammable limit (LFL), there is an ignition source, and the air velocity is lower than the burning velocity. When leakage occurs from an air conditioner, there is always a region where the refrigerant concentration is higher than the LFL because the refrigerant concentration is 100% near the outlet from the air conditioner. Thus, understanding the refrigerant diffusion phenomena of low-GWP refrigerants is important to acquiring sufficient information for developing safety standards to assess the risks of using these refrigerants. Numerical analysis is an effective tool because it is very difficult to measure the diffusion of a refrigerant in a large space. In this study, diffusion phenomena were numerically analyzed when a refrigerant leaked slowly from a room air conditioner (RAC) and package air conditioner (PAC) and rapidly from a chiller into a large space. Based on the calculation results, the refrigerant concentration distributions, the volumes and positions of the flammable regions, and their changes in time were examined.