Effect of Central Fans and In-Duct Filters on Deposition Rates of Ultrafine and Fine Particles in an Occupied Townhouse.
Effect of Central Fans and In-Duct Filters on Deposition
Rates of Ultrafine and Fine Particles in an Occupied
Townhouse.
(423 K)
Wallace, L. A.; Emmerich, S. J.; Howard-Reed, C.
Atmospheric Environment, Vol. 38, No. 3, 405-413,
January 2004.
Keywords:
fan; filters; ducts; housing; ultrafine particles; fine
particles; deposition; filtration; air cleaner; field
study
Abstract:
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 (ESP) and fibrous
mechanical filters (MECH). Deposition rates are
calculated for 128 size categories ranging from 0.01 to
2.5 m. 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, MECH installed, ESP installed. For all cases,
deposition rates varied in a "U"-shaped distribution
with the minimum occurring near 0.1 m, 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 0.10.5 h-1. The MECH
increased deposition rates by up to 2 h-1 for ultrafine
and fine particles but was ineffective for particles in
the 0.10.5 m range. The ESP increased deposition rates
by 23 h-1 and was effective for all sizes. However, the
ESP lost efficiency after several weeks and needed
regular cleaning to maintain its effectiveness. A
reduction of particle levels by 50% or more could be
achieved by use of the ESP when operating properly.
Since the use of fans and filters reduces particle
concentrations from both indoor and outdoor sources, it
is more effective than the alternative approach 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.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899