The building envelope as an air filter.

Recent research suggests that fine-particulate air pollution increases the incidence of lung disease and premature death. In this paper, single fibre filter theory was used to predict the theoretical particulate collection efficiency of air permeable walls (dynamic insulation). The relationship between particle diameter and filtration efficiency for dynamic insulation, as a function of flow rate, is examined and compared to that for a conventional filter. Factors such as filter penetration as a function of flow rate, filter thickness, and packing density for a range of particle diameters are also presented. The findings suggest that, in addition to reducing heat loss through the building fabric, dynamic insulation can act as a high performance air filter in naturally ventilated buildings, thus providing a viable and attractive alternative to mechanical air-conditioning in congested urban environments