Air cleaners and other
appliances for keeping air clean
By: Dr. Harriet
Burge
Although it is entirely possible
to design and construct buildings that provide clean air, many old buildings were not designed with clean
air in mind, and many new buildings are either designed without consideration of air quality, or are
constructed in ways that allow the intrusion of water, pests, and other air pollutant sources.
Because of increasing concerns
about mold and other air quality concerns, many appliances are now on the market that claim to provide
clean air, even in situations where sources are present. The question is do they work, and if so, how
well?
In the first place, no amount of
air cleaning is going to render a leaky moldy building acceptable for occupancy. The only solution to
continuing water problems is to find the cause, fix it, and remove all existing mold growth. Given that
water leaks have been repaired, then it is possible that free-standing appliances could prevent some mold
growth (dehumidifiers), or remove residual spores as well as spores that might enter on peoples' clothes
and from the outdoors (air cleaners).
Console dehumidifiers actually
do work to lower humidity and may prevent condensation that might lead to mold growth. I would recommend
dehumidifiers for anyone who does not have a bathroom or kitchen fan to remove vaporized water from cooking
or bathing. I would also use a dehumidifier in any below-grade basement space. There are dehumidifiers on
the market that can reduce humidity in an entire 1,000 square foot basement to below 40% and keep it there
(e.g., the Santa Fe Rx sold by the Therma-Stor). With this kind of dehumidification, a basement will not be
damp and moldy unless, of course, there is actual water intrusion.
Air cleaners present a more
complex question. First, appliances that "ozonate" or "ionize" the air without actually capturing particles
inside the units cannot be recommended. There are two general kinds of air cleaners that do capture
particles from the air that passes through: fan driven filtration devices, and electrostatic precipitators
which may or may not be fan driven.
Filtration devices use fans to
force air through filters onto which airborne particles impact, thus being removed from the air stream. The
efficiency of these devices depends on the particle collection efficiency of the filter (which is near 100%
for the HEPA units) and on the rate at which air passes through the unit. The actual steady-state
concentration of particles in the space during air cleaner operation also depends on the number and
strengths of sources in the space. No air cleaner will keep all the spores out of the air in a room with
the walls covered with mold. Nor will such a cleaner remove moldy odors. On the other hand, a high speed
fan driven unit with a HEPA filter will reduce particle levels in a room with little or no mold to near
zero very quickly, and will maintain relatively low levels providing the unit operates continuously and is
properly maintained.
The principle problem with
fan-driven air cleaners is the noise produced by the fan. Unfortunately, the better the filter, generally
the more powerful the fan needs to be, and the more noise is produced. There is good data available
documenting that people turn off air cleaners because of this noise, even in occupational spaces where the
airborne particles are clearly hazardous (e.g., radioactive). No air cleaner will work if it is not turned
on!
A relatively new air cleaner on
the market today uses electrostatic precipitation to capture charged particles from air that is moved past
the precipitating plates by a so-called "ionic breeze". Actually, the physics of the ionic breeze air
movement has been known for more than 100 years. The corona discharge that charges particles so that they
are attracted to the precipitating plates also ionizes the air, and the air ions also tend to move toward
the plates. The amount of air movement generated by such a process depends on the voltage applied to create
the corona discharge. Currently, available models move between 1.5 and 2 m3/minute. This is not as much as
a high-speed fan will move, and it takes generally about 30 minutes for particles in an average size room
to reach less than 1% of original concentrations. On the other hand, the units are silent, use little
electricity, and do remove particles from the air.
In summary, fix water leaks and
remove mold. Use dehumidifiers to limit condensation. For very sensitive people who can stand the noise,
fan-driven air cleaners may be helpful. For those who do not need the fast cleaning provided by the
fan-driven units, the silent Ionic Breeze sold by The Sharper Image can be used to reduce exposure to
residual mold spores or those that seep in through cracks and on clothing.
The reader is strongly cautioned
that none of these appliances substitute for good investigation and appropriate remediation of conditions
allowing mold growth and removal of the mold itself.
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