Study of particle and ozone penetration through the building envelope

Outdoor pollutants, such as particles and ozone, can penetrate through the wall assemblies and influence the indoor air quality. The objectives of this study are to (1) develop methods to model and simulate particle and ozone penetration through the wall assembly; and (2) improve the understanding of particle and ozone penetration by experimental measurements. This study developed a modeling framework for predicting particle and ozone penetration through building envelope systems. The transport process of 0.001-10 µm particles in the cracks were simulated by Eulerian-Eulerian method, while particle transport in the fiberglass was accounted for by an additional sink term in the governing equation, derived from the classical filtration theory. The transport process of ozone through leakage paths was numerically simulated by two approaches: (1) species transport model plus 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: transport-limited deposition and 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. The results showed that 0.05 µm-1 µm particles were the most penetrable particles, though fiberglass insulation media greatly reduced particle penetration by more than 90% when air permeability of the insulation is larger than 0.001s. 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 ozone penetration factors by species model and UDS model were in good agreement. Fiberglass insulation media reduced ozone penetration by more than 60% under almost all circumstances when reaction probability was larger than 10 -8 . This study also reported data of particle penetration through a mid-scale wall assembly with cellulose fiber insulation. For particles of sizes between 0.5 and 2.5 µm, the penetration factors varied between 0.15 and 0.6, consistent with the numerical simulation