Numerical simulation of ozone penetration through the wall assembly

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, α pinene, β pinene and 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. New approaches were developed to account for the effects of fiberglass insulation on penetration factors. The transport process of ozone through leakage paths was numerically simulated by two approaches: 1) species transport model plus pseudo first order chemical reaction model; and 2) user-defined scalar transport model plus user-defined deposition model. A simplified method to simulate ozone transport through fibrous media was also developed 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 in the vertical direction and 3 mm in the horizontal direction and with fiberglass insulation width of 0.14 m. Theoretical analysis showed that gas phase reaction between ozone and unsaturated VOCs emitted from wall materials in leakage paths and fiberglass insulation could be neglected compared with the surface reaction. The calculated penetration factors by species model and UDS 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.