The composition and location of dust settled in supply air ducts.

The amounts, quality and factors affecting of dust accumulation in supply air ducts of eight nonindustrial buildings were studied. The average of surface density of dust settled in supply air ducts was 10.6 g/m² and the average of yearly accumulation rate was 3.5 g/m²*year. The dust contained 82% of inorganic material, which agrees well with the composition of outdoor air dust in down town areas. In straight air duct the surface density of settled dust decreased as a function of distance from the air handling unit (AHU). The dust was mainly settled on the bottom of the duct and captured by the residues of lubricant oil used in manufacturing of ducts. In some cases soil depris was settled during the building construction period. The floor of the building did not affect the amount of settled dust. Fungal genera was similar to found in outdoor air and microbial growth in the air ducts was not observed in this study. The proportion of pollen grains was 70 mg/g of dust and it varied widely according to plants in surrounding environment. The results show that leakages between filter cassette and assembly frame were common in AHU of nonindustrial buildings.