System Solutions
What to Look For in a Contractor
Product Information
Air Filtration
Cooling Products
Furnaces
Weather Control
Maintenance
Facts on Indoor Air Filtration
Once you could clearly see if your home was clean. Today we are also
concerned about the things that we cannot see, particularly the air in our
homes. In an effort to make our homes more energy efficient we are making
them tighter. One side effect of tight constructions often is an undesirable
level of indoor air pollutants. Such pollutants are particles of dust, dirt,
pollen, tobacco, cooking smoke, and viruses. These particles can cause itchy
eyes, sneezing, and other allergy symptoms. These particles can also coat
you heating and cooling equipment and lower their efficiency.
You can control these pollutants in a number of ways. You can reduce the
contaminates that enter your home by keeping the windows closed to reduce
dust, using exhaust fans to exhaust smoke and odors, and reducing the amount
of use of aerosol and household cleaners that produce chemicals. Once
present you can remove the particles from your home with a variety of air
cleaners. (These air cleaners will be discussed later in this article.)
We can, however document the effects of a particular filter on the heating
cooling system. A furnace fan is designed to deliver a certain amount (cfm)
of air at any given resistance (assume a typical system may deliver 1200 cfm
at.5" wg). The ductwork, fittings, air conditioner coil, registers, and
filter all make up the total resistance. The problem with many "high
efficiency" filters is a high resistance or pressure drop. One manufactures
data shows a filter with an initial resistance of .15"wg. They do not stop
testing until they measure a final resistance of 1" wg. With a typical home
furnace fan the following will happen: The fan will deliver its rated amount
with a clean new filter. You will receive all the warm or cool air that you
paid for and you will be comfortable. As the filter gets dirty, the air flow
will go down, you will not get all the warm or cool air as before, and
therefore, you will be less comfortable. As the filter reaches a resistance
of 1" wg, the total resistance is more than the fan can overcome. The
furnace overheats and cycles on its high limit. The air conditioner freezes
up and system life is shortened. You are extremely uncomfortable.
Make sure you ask about pressure drop of a filter. Look for low initial and
operating pressure drop. Question the practicability of any filter that ends
its testing with a resistance higher than any residential furnace can
operate at.
Dust and other contaminates vary greatly in size. The larger the particle,
the easier it is to remove. As a reference the human hair has a diameter of
about 100 microns. About 99% of airborne particles are smaller than a
micron. Weight is also important, obviously the larger the particle, the
more it weighs.
Filtration efficiency ratings include arrestance, dust spot, and particle
size. Arrestance is the rate by weight of dirt removed. A high arrestance
rating does not necessarily mean a high efficiency filter. Remember that
large particles weigh more and are easier to trap. Therefore, a filter could
stop a few large particles with high weight, allow all the small particles
with low weight to pass through, and still have a high arrestance rating.
The dust spot rating is how much a filter can slow down staining around a
diffuser. This same filter may yield a wide variety of results. The third
rating of particle size efficiency is the ability to remove specific sizes
of airborne particles. Unfortunately there is no standard rating system or
independent certification authority to publish cooperative data. Therefore,
consumers are left with manufactures' data that needs to be verified by only
one test run by a testing firm hired by the manufacturer.
Level 1. Fiberglass or Washable Hogs Hair- This is the standard filter, and
is usually 1" or 2" thick. It will remove particles larger than 10 microns.
It has a typical dust spot rating of 3%-5%. You can throw the dirt away with
the filter and start over clean.
Level 2. Fabric-This is a newer style of filter and costs a little more than
the standard filter. It is also 1" to 2" thick, and is pleated for more
surface area. It has a higher air flow resistance. It has a typical dust
spot rating of 30%-35%. You can still throw the dirt away with the filter.
Level 2. Electrostatic-This filter is usually made of 2 or more layers of
synthetic material that generates static electricity as air passes through
it. These filters have the potential for very high air flow resistance. It
has a typical dust spot rating of 20%. These filters are washable, however
they are usually difficult to clean. Therefore, you usually put the filters
back with some of the old dirt still in it. The pressure drop will rise
quickly throughout the life of the filter.
Level 3. Mechanical-This filter uses a highly pleated media of a glass
fiber. This filter has about 75-80 square feet of filter surface due to the
high number of pleats. The initial pressure drop is low, but will raise 0.5
inch and has a dust spot rating of 75%-80%. The media is disposable allowing
you to throw away the dirt.
Level 4. Electronic-This is the most effective of all filters. It works by
applying high voltage (7000 volts) to wires at the front of the filter.
Grounded plates attract and hold the charged particles. The plates are
washed to remove the dirt. This filter has a very low pressure drop and a
dust spot rating of up to 95%.
What type of filter is best for you? There is some discussion about
mechanical vs. electronic air cleaners. When clean, the
electronic filters are the most efficient. These filters
require frequent cleaning and may have some repair costs associated with
them. The mechanical filter is very maintenance friendly
and requires a media change once or twice a year. The
level 2 media filters are a little better than the standard disposable
filters. Both filters should be replaced monthly for best system
performance. The electrostatic filters are not recommended for most
installations. The pressure drop is much too high for proper equipment life
and operation. Maintenance is high and it is difficult to remove all the
dirt in the filter. Long term operation and shorter equipment life are all
possible. It is clear to see that most homeowners wanting clean air, either
an electronic or mechanical air cleaner is the best value.
We also have other options for clean air. The first is a true HEPA type filter manufactured by Abatement Technologies. These filters are quite expensive but will be worth the money for people with severe allergy conditions. The second is a UV air purifier manufactured by Sanuvox. Ultra-violet light has been shown to kill bacteria, mold, and viruses circulating in the air. Please call us for more information in these and other products to help clean the air you breath.
An Authorized
Carrier Products Dealer
© 1998 - Hinrich Incorporated