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What is an Electostatic
Air Cleaner?
Electrostatic
precipitators are commonly used to remove particles from airstreams
having large steady flow rates. Typical applications include
coal-burning plants and cement kilns. A typical two-stage electrostatic
precipitator has a stage of corona wires and a stage of collecting
plates. The corona wires are maintained at several thousand volts
which produces a corona that releases electrons into the airstream.
These electrons attach to dust particles and give them a net
negative charge. The collecting plates are grounded and attract
the charged dust particles. The collecting plates are periodically
rapped by mechanical rappers to dislodge the collected dust,
which then drop into hoppers below. The air velocity between
the plates needs to be sufficiently low to allow the dust to
fall and not to be re-entrained into the airstream.
It takes between 0.01 and 0.1
second for dust particles to acquire a charge in the corona region.
Industrial systems are normally designed with more than 1 second
residence time in the first stage to assure the charging of dust
particles. Industrial systems are capable of removing particles
in the size range 0.01 -- 10 microns and can achieve efficiencies
in the neighborhood of 95%.
Small
electrostatic precipitators designed for home or other non-industrial
applications are known as electronic air cleaners. These do not
have rappers, but must be taken apart and cleaned periodically.
Also, these devices are often inserted into airstreams without
regard to residence time or air velocities, and hence efficiencies
can be much lower than those used in industrial applications.
A well-designed electronic air cleaner for home or office building
applications would not only be relatively large and have a high
energy demand, but it would also generate ozone at potentially
hazardous levels.
Even a well-sized, efficiently
operating air cleaner cannot achieve the efficiency necessary
to guarantee complete interception of airborne bacteria, let
alone viruses. However, as a means of simply improving air quality
and decreasing dust and airborne microbes, electronic air cleaners
do indeed have some value in home and office building environments.
Source: Aerobiological
Engineering, Pennsylvania State University
Furnace Problems
Electrostatic air filters are
too dense for most furnaces. As a result, they can interfere
with the airflow of the furnace, causing the air conditioner
to freeze up in the summer. Electrostatic air filters can also
cause the furnace to overheat in the winter.
Maintenance
Electrostatic air filters require
frequent cleaning, usually more than once a month. They cannot
just be installed and forgotten about. Unfortunately, they are
usually neglected because most people simply do not remember
to get inside the furnace at least once a month to clean the
filter and re-install it. Even if you did, this routine is still
a pain because electrostatic air filters usually have several
layers you have to remove and clean individually.
Effectiveness
The problem with electrostatic
and all other air filters is that they can only remove the larger
airborne particulates. What they fail to mention is that most
airborne pollutants are smaller than the 0.3 microns that they
are capable of removing. Allergens, particulates and toxins from
cigarette smoke, etc. still manage to slip through these screens
and back into the air we breathe.
Black Wall Effect
Electrostatic air filters work
by electrically charging particles so they are attracted to the
metal plates in the machine. However, these charged particles
are also attracted to all surfaces, resulting in black markings
on walls, etc.
If an electrostatic filter is
not the solution, then what is?
Cutting-Edge
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even remove volatile organic compounds (VOCs) that come from
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not remove gaseous VOCs. Additionally, even if a HEPA filter
traps bacteria, germs and viruses, it doesn't kill them.
Biozone® Air Purifiers use
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SafeZone™
is the ultimate in ozone safety. SafeZone™ will not allow
the accumulation of ozone to exceed recommended, safe levels
when the units are operated as directed. It is a fail-safe method
that does NOT rely on electronic gadgetry or inexpensive sensors
frequently used by other manufacturers to regulate the ozone
output of their units. When operating a Biozone® Air Purifier,
when the ozone level in the environment begins to rise, the amount
of ozone produced by the unit is automatically reduced.
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