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Air Filters
The common types of air filters
Cost and maintenance requirements should be
a key consideration when you explore what type of air filters you
are going to select. The basic types of air filters include:
Panel filters
Panel filters are
inexpensive to buy-they cost between 50 and $5-but they have
dust-spot efficiencies of less than 5%. Their filtering capability
actually increases as they get dirty, but this is accomplished at
the expense of restricting air flow and increasing pressure drop. To
avoid restricting air flow, they should be changed every one to
three months. They do a poor job of protecting the forced-air system
and offer human lungs almost no protection from particles.
Electrostatic
air filters
Electrostatic panel filters are a little
more effective than standard panel filters because they rely on
static electricity to attract charged particles in the airstream.
Either the static electricity is created by air as it flows through
the filter, or the filter is manufactured with precharged electrets
made from a propylene, polypropylene, or other plastic material. The
electrets are permanently charged with both positive and negative
charges. As air flows past the charged filter material, oppositely
charged particles in the airstream cling to the filter's fibers.
High-Efficiency
Particulate Air Filters (HEPA)
High-efficiency particulate air (HEPA)
filters achieve the maximum efficiency available, with dust-spot and
DOP test values greater than 97.99%. However, HEPA filters greatly
restrict air flow and require special blowers and duct design. They
are usually found in "clean room" applications in industrial or
commercial settings, rather than residences
Extended surface
filters
An electronic air cleaner, or
electrostatic precipitator, uses high voltage to charge particles in
the return airstream. The charged particles are collected on an
oppositely charged metal plate. Electronic air cleaners achieve
dust-spot efficiencies of over 90% with little air flow restriction
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