VOC source and sink behaviour of porous building materials: Part I model development and assessment

Evaluating the VOC source and sink behaviour of porous materials is important for thedetermination of the VOC concentration levels in indoor air environment. The transfermechanisms involved in the source and sink behaviour are the same, but the mass transferis in the opposite direction (i.e. from material to air for source, and from air to material forsink). This paper presents a mass transfer model that can be used to predict both sourceand sink behaviour of porous materials. The model considers internal diffusion, sorptionand VOC generation due to secondary emissions other than sorption within the solid, andthe convective mass transfer over the solid with the third-kind boundary condition. Theexact analytical solution was obtained using the integral transform method.The performance of model prediction was assessed for primary source and sink behaviour.This involved comparison of the predictions made by the proposed model with those ofthe analytical model by Little et al. (1994) as well as the environmental chamber test datafor emissions and sorption. The prediction of the proposed model agrees well with the testdata. The proposed model and Littles model generally agree well after the early stagewhen the internal diffusion dominates. However, at the early stage, Littles model tends tooverestimate the emission or sorption rates as compared with the proposed model, sinceLittles model does not consider the boundary layer resistance due to convection.