What Types of Air Cleaners are Available?
excerpted from:
EPA: Residential Air Cleaning Devices: A Summary of Available Information
Office of Air and Radiation (OAR)
EPA 400/1-90-002, February 1990
Air cleaners are usually
classified by the method employed to remove particles of various sizes from the air. There
are three general types of air cleaners on the market: mechanical filters, electronic air
cleaners, and ion generators. Mechanical filters may be installed in ducts in homes with
central heating and/or air-conditioning or may be used in portable devices which contain a
fan to force air through the filter. Mechanical filters used for air cleaning are of two
major types. Flat filters may efficiently collect large particles, but remove only a small
percentage of respirable size particles.
Pleated or
extended surface filters generally attain greater efficiency for capture of respirable
size particles than flat filters. Their greater surface area allows the use of smaller
fibers and an increase in packing density of the filter without a large drop in air flow
rate.
Electronic air
cleaners use an electrical field to trap charged particles. In electrostatic
precipitators, particles are collected on a series of flat plates. In charged-media filter
devices, which are less common, the particles are collected on the fibers in a filter. Ion
generators also use static charges to remove particles from indoor air. These devices come
in portable units only. They act by charging the particles in a room, so they are
attracted to walls, floors, table tops, draperies, occupants, etc. In some cases, these
devices contain a collector to attract the charged particles back to the unit. (Note: The
latter two types of devices may produce ozone, either as a byproduct of use or
intentionally. Concerns about ozone production are discussed in more depth later.) Some
newer systems on the market are referred to as "hybrid" devices. They contain
two or more of the particle removal devices discussed above.
In addition to
particle removal devices, air cleaners may also contain adsorbents and/or reactive
materials to facilitate removal of gaseous materials from indoor air. Air cleaners which
do not contain these types of materials will not remove gaseous pollutants.
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