Environmental Engineering Reference
In-Depth Information
4.
Air cleaner use problems
Air cleaners are often purchased by consumers in response to physician
recommendations or as a result of a personal desire to alleviate symptoms
of allergy, asthma, or other building-related health concerns. Consumers
and physicians are unaware of the limitations of air cleaners and their use
in general, and limitations of specific air cleaner types and models. With the
possible exception of negative ion generators, desktop devices are appar-
ently ineffective. Portable and in-duct extended-media filters, on the other
hand, can be used effectively if selected for the appropriate reason and
operated properly.
Individuals often purchase air cleaners for generic use in alleviating
allergy symptoms, ostensibly by reducing airborne allergen levels. Unfortu-
nately, only a few airborne allergens are amenable to significant control by
air cleaning. These include mold spores and hyphal fragments, and pet
allergens when pets are no longer present to actively produce allergen. Dust
mite fecal pellets and fragments are very large (>10
m) and do not remain
airborne for more than 10 minutes or so. Exposure occurs on disturbance.
The same is likely true for cockroach allergens as well. For such allergens,
air cleaning is unlikely to have any measurable benefit.
Though in-duct cleaning devices have the potential to significantly
reduce airborne levels of mold and other small particles, air cleaning can
only occur when the blower fan is operating. In residences using in-duct
systems, the blower fan is usually not wired to allow blower fan operation
independent of heating/cooling system activation. In residences where inde-
pendent operation of blower and heating/cooling systems is possible, resi-
dents are rarely aware that good system performance requires continuous
or near-continuous operation.
Consumers often purchase a portable air cleaner with the assumption that
it can clean the air of a whole house if it is operated in a central location. Such
portable devices have relatively low design and actual air flows (compared
to in-duct systems). Performance decreases with increasing air volume when
flow capacity is insufficient. Portable air cleaners achieve their best perfor-
mance in single closed rooms (e.g., bedrooms). Good performance depends
on air cleaner placement; in most cases, placement near the center of the room
or near an allergy patient's nighttime breathing zone is recommended.
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5.
Ozone production
Electronic air cleaners and negative ion generators employ high voltages
which cause ionization. Consequently, they have the capability to produce
significant quantities of O
. Because of its toxicity at low concentrations, its
potential effects on rubber products, soft plastics, and fabric dyes, and its
role in initiating indoor chemical reactions that produce irritants; O
3
produc-
tion by such devices is of concern. Products sold as medical devices are
regulated by the Food and Drug Administration (FDA). The FDA limits O
3
3
emission from these products so that an indoor level may not exceed 0.05
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