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Whole House HEPA Air Cleaners
and Filtration Systems for Allergy Relief
By Gary Cerantola, P.Eng., MBA
Everyone has a physical tolerance level for airborne chemicals and
particulates. Some people have a higher tolerance than others for dirty air, but it affects
everyone. Children whose respiratory system is still developing are at greater
risk of asthma or allergies if they are exposed to many airborne contaminants.
Increased levels of contaminants in the air can even affect the well-being of
fully developed healthy adults.
The higher the level of contaminants in the
air, the quicker a person can reach their tolerance level. Then the contaminants
could start to damage their respiratory system and their general health.
Significant reduction of contaminants in the home can help the body recover from
constant exposure to contaminants outside the home. We like to say this
reduction in the stress to our respiratory system can be compared to a good
nights sleep for a tired athlete.
What the heck is a "HEPA" filter?
HEPA is a filtration standard created by the U.S. Atomic Energy Commission.
HEPA stands for “High Efficiency Particulate Air”. Some providers refer to HEPA
as “High Efficiency Particulate Arresting”. Both terms refer to the same
technology. HEPA filter media is proven to be 99.97% efficient @ 0.3 microns (a
micron is 1/1,000,000 of a meter or 1/25,000th of an inch). Due to their
extremely high efficiency, HEPA filters have become widely used in medical,
electronic and industrial applications. In particular, HEPA is the air
purification method used in operating rooms, clean rooms, space research and
The graphic below shows the relative size of particles that
can be removed by air filters. HEPA filters can remove particles finer
than smoke! Amazing!!
HEPA filters are composed of a various sized borosilicate fibers, which are
pressed together to form a netlike structure with openings large enough for air
to pass through but too small for most particulates.
HEPA air cleaners are effective in controlling:
- Household dust
- Animal dander
- Dust mite feces.
Good HEPA air cleaners incorporate both activated carbon and/or zeolite for odor
and gas control, in addition to particle removal.
Carbon Volatile Organic Compound (V.O.C.) Blankets:
Like Carbon Pre-filters, the Carbon Inner Blanket is placed in the air
purifier as an additional purification media. It is a form of charcoal which has
the ability to remove impurities from air, gas, and liquids. When various
impurities come into contact with the activated carbon, the constituent
molecules become trapped in tiny capillary passages on the surface of the carbon
in a process called adsorption. Due to differences in molecular structures, some
impurities are more readily adsorbed than others.
Carbon/Zeolite V.O.C. Cartridges:
V.O.C. cartridges can also make up part of the cleansing capability of the
air purifier. These cartridges capture contaminants the same way as a
Carbon Blanket, but they use solid carbon and zeolite pellets which have a
comparably larger surface area. This makes V.O.C. cartridges the filter of
choice for situations where V.O.C. removal is a prime objective.
Since HEPA filters coupled with additional air cleaning capability have a
very high air resistance, they cannot be installed directly in-line in a Heating
and Ventilation and Air Conditioning (HVAC) system. Instead, whole house HEPA filtration systems must be installed in a by-pass
configuration using a separate blower motor system.
Figure 1.0 HEPA Whole House Filter By-Pass
Because HEPA units work on the air exchange principle - air is cleaned by
continually pulling air from the room into the filtering/cleaning device and
exhausting clean air - their effectiveness is determined by calculating the
number of air exchanges per hour in a given area.
The greater the number of air changes in a home that occurs, the cleaner the
air. To calculate air changes per hour (ACH) for your particular home and
particular HEPA unit you can use this formula:
One air change occurs in a room when a quantity of air equal to the volume of
the room is filtered by the HEPA filter unit. Air change rates are units of
ventilation that compare the amount of air moving through a space to the volume
of the space. ACH is the volume of air (usually expressed in cubic feet) moved
every hour divided by the room volume (also usually expressed in cubic feet).
Airflow is usually measured in cubic feet per minute (CFM). Your HEPA filter
blower will have a CFM rating assigned to its blower. This is multiplied by 60
minutes to determine the volume of air filtered through the unit per hour (in
To calculate room volume (in cubic feet), multiply average room height (in feet)
by the room area (in square feet). Room area is the room width (in feet) times
the room length (in feet).
ACH = airflow per hour/room volume =CFM X 60 minutes/cubic feet
It is important to be aware of how air contaminants can affect our health and
to adopt corrective measures that will improve indoor air quality in our homes.
Whole House HEPA/air cleaners and filtration systems are one alternative
available to the homeowner to positively affect their homelife environment to reduce:
- Particulates (air pollutants that have mass) like dust, dander,
pollen, and cigarette smoke
- Volatile Organic Compounds (V.O.C.s) which are gases from
chemicals that are released into the air by various household materials and
liquids such as housecleaning chemicals, detergents and building materials.
- Bio-Burden is the amount of biological material in the air, living
or dead. Dead material can cause allergic reactions, living material can
cause allergic reactions some can cause disease.
About the author: Gary Cerantola is a professional
engineer and chemist having worked in the areas of water treatment and
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