Accurate modelling of the material volatile organic compounds (VOC) emission rate in the building is important for predicting the contaminant concentration, occupant exposure and for the design of mechanical ventilation systems. The material emission rate is controlled partly by internal diffusion as result of concentration gradient and partly by surface emissions by convection or evaporation due to the interaction of the material surface with adjacent air. Recently, there has been a growing interest in the development of mathematical models to predict the quality of indoor air, and several models based on the principles of fluid flow and mass transfer have been developed and validated.
An integrated IAQ model was developed to predict volatile VOC emission rate of a multi-layer material, VOC sink rate of a material, room air VOC concentration with both VOC source and sink materials, and VOC concentration distribution within a material. There was good agreement between the predictions made by the integrated model and experimental data.
The model was first applied to a room with a typical floor assembly (vinyl floor tile/glue/plywood) to study the multi-layer material VOC emissions. Results indicate that the multi-layer material first shows the same emission characteristics as the top layer material, and the top layer material strongly delays VOC emission from the bottom layer material. The multi-layer material has a much longer VOC emission time and slower VOC decay rate than the single-layer material. The model was further applied to a room with a floor assembly (vinyl floor tile/glue/plywood) as the source material and with plywood walls as the sink materials. Results show that the plywood substrate in the floor assembly significantly affects the VOC emission rate from floor assembly. Results also show that the plywood wall sink effect reduces VOC concentration in the room air initially and elevates it as the time progresses. However, the plywood sink impact on VOC emission rate and room air VOC concentration is not significant.
The model uses four parameters: the diffusion coefficient of each material layer; the material/air partition coefficient of each material layer; the initial concentration in each material layer; and the convective mass transfer coefficient. 22 refs.