A mathematical model of critical releasable charge for R290 indoor leakage of split-type household air conditioners

Abstract

The leakage of hydrochlorofluorocarbons and hydrofluorocarbons used as refrigerants will not only cause ozone depletion and global warming, but also pollute indoor air. Propane (R290) not only does not damage the ozone layer and has a negligible greenhouse effect, but also its charge is about 20–50% of that of hydrochlorofluorocarbons and hydrofluorocarbons, and the releasable charge is lower. In the previous study, a refrigerant pump-down method was proposed to control the R290 releasable charge of split-type household air conditioners (STHACs) under off-mode below the critical releasable charge (CRC) to prevent fires. CRC varies with leakage conditions, such as leak hole sizes, the distance between the installation height of the indoor unit (IDU) and the ignition source (dispersion distance), and the construction of IDU, etc. In this study, a mathematical model is developed to predict the CRCs for STHACs with different capacities and constructions under various leak conditions. The model is verified to have a deviation within 10% for the vast majority of data-points by ignition experiment and CFD model. For safety, the CRC prediction formula is optimized to under-predict CRCs properly, therefore, CRCs for various STHACs and leak conditions are determined to prevent the formation of flammable mixtures even directly under IDU, and the indoor air quality will also be improved. For the used 1 HP STHAC, the predicted CRC is 6.6 g under a 0.5 mm2 leak hole and a 0.7 m dispersion distance.