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Effect of Central Fans and In-Duct Filters on Deposition Rates of Ultrafine and Fine Particles in an Occupied Townhouse



L A. Wallace, Steven Emmerich, Cynthia H. Reed


Airborne particles are implicated in morbidity and mortality of certain high-risk subpopulations. Exposure to particles occurs mostly indoors, where a main removal mechanism is deposition to surfaces. Deposition can be affected by the use of forced-air circulation through ducts or by air filters. In this study we calculate the deposition rates of particles in an occupied house due to forced-air circulation and the use of in-duct filters such as electrostatic precipitators and mechanical filters. Deposition rates are calculated for approximately 140 size categories ranging from 0.01 to 2.5 mm. More than 110 separate events (mostly cooking, candle burning, and pouring kitty litter) were used to calculate deposition rates for four conditions: fan off, fan on, mechanical filter installed, electrostatic precipitator (ESP) installed. For all cases, deposition rates varied in a U -shaped distribution with the minimum occurring near 0.1 mm, as predicted by theory. The use of the central fan with no filter or with a standard furnace filter increased deposition rates by amounts on the order of 0.1-0.5 h-1. The mechanical filter increased deposition rates by up to 2 h-1 for ultrafine and fine particles but was ineffective for particles in the 0.1-0.5 mm range. The ESP increased deposition rates by 2-3 h-1 and was effective for all sizes. However, the ESP lost efficiency after several weeks and needed regular cleaning to regain its effectiveness. A reduction of particle levels by 67% or more could be achieved by use of the ESP when operating properly. Since this reduction applies both to indoor and outdoor sources, it is more effective than the approach recommended by certain agencies of reducing ventilation by closing windows or insulating homes more tightly. For persons at risk, use of an air filter may be an effective method of reducing exposure to particles.
Atmospheric Environment
No. 3


air cleaner, deposition, field study, filtration, fine particles, Ultrafine particles


Wallace, L. , Emmerich, S. and Reed, C. (2004), Effect of Central Fans and In-Duct Filters on Deposition Rates of Ultrafine and Fine Particles in an Occupied Townhouse, Atmospheric Environment, [online], (Accessed May 21, 2024)


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Created December 31, 2003, Updated October 12, 2021