Numerical investigation on flammability of R32 leakage in heat pump outdoor unit with CFD simulation

R32 is receiving significant attention as an alternative refrigerant owing to its higher operating efficiency and lower environmental impact; however, it is classified as flammable refrigerants. There have been some studies on R32 leakages about indoor unit rooms but extremely limited studies about outdoor unit rooms. The outdoor unit room is more cramped than the indoor one, and leakage easily occurs due to high-temperature and high-pressure operating conditions. In this study, the flammability risk was evaluated through a comprehensive R32 leak study in the outdoor unit room. Critical factors including the leak diameter, unit installation height, refrigerant charge, air infiltration, window opening, and room size were carefully selected, and parameter studies and correlation analysis were conducted. As the leak diameter increased from 2 to 8 mm, the R32 volume fraction increased from 7.7 to 46.3%, indicating that the leak diameter is the most significant factor in increasing the R32 volume fraction. Considering that the leak diameter is less than 1 mm in a typical leak accident and the leak occurs with a diameter of 2 mm or more in a catastrophic case, the risk of R32 leak was found to be low under the conditions. By increasing the window opening and unit installation height, the concentration of R32 can be lowered below the LFL, thereby reducing the flammable volume to close to zero.