Modeling ozone penetration through the wall assembly using computational fluid dynamics

Outdoor pollutants, such as ozone, can penetrate into the indoor environment through the wall assemblies and influence the indoor air quality (IAQ). Ozone can also react with chemical compounds (i.e., d-limonene, -pinene, -pinene, styrene, etc.) within the wall assemblies to create secondary emissions causing IAQ concerns. This study developed a modeling framework for predicting ozone penetration through building envelope systems. The transport process of ozone through leakage paths was numerically simulated by two approaches: (1) a species transport model plus a chemical reaction model and (2) a user-defined scalar (UDS) transport model plus a user-defined deposition model. A simplified method to simulate ozone transport through fibrous media was also developed in a UDS model based on the analysis of two deposition mechanisms: (1) transport-limited deposition and (2) surface uptake of the fiber. The model was successfully applied to a typical residential wall assembly, assuming crack heights of 1 mm (0.04 in.) in the vertical direction and 3 mm (0.12 in.) in the horizontal direction and with fiberglass insulation width of 0.14 m (5.5 in.). Theoretical analysis showed that gas phase reaction between ozone and unsaturated volatile organic compounds emitted from wall materials in leakage paths and fiberglass insulation could be neglected compared with the surface reaction. The calculated penetration factors through leakage paths by the species transport model and UDS transport model were in good agreement. Fiberglass insulation media greatly reduced ozone penetration by more than 60% under almost all circumstances when reaction probability was larger than 10 ⁸.