Allowable Charge Calculation Method for Flammable Refrigerants

Although hydrocarbons and lower GWP HFCs are flammable, they are preferable to high GWP HFCs from the perspective of mitigating climate change. Appropriate standards are necessary to utilize these refrigerants so that their flammability risks are minimized. Although standards for the use of flammable refrigerants exist, some reports indicate that the refrigerants can sometimes be ignited even at levels which satisfy the standards. In addition, the theoretical background of these standards is unclear. To promote the development of a more appropriate standard, a more scientific method for calculating the allowable refrigerant charge was established. Because the calculation method was proposed as the foundation for a new international standard, a relatively simple formula was developed, based on experimental and numerical (CFD) analyses. NOMENCLATURE CFD; Computational Fluid Dynamics h1; Effective height in 7m 2 room [m] GWP; Global Warming Potential K; Coefficient for adjusting charge amount HFC; Hydrofluorocarbons other than propane HCs; Hydrocarbons LFL; LFL in we1gm L kg/m] UFL; Upper Flammable Limit mmax; Allowable charge [kg] LFL; Lower Flammable limit t; Leak duration [minutes] A; Floor area [ m] x; Height from the floor [ m] h; Effective Height [m] y; Concentration of refrigerant [kg!m] h0 ; Leak height (Installation Height) [m]