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Clean Air Delivery Rate (CADR) indicates
the volume of filtered air delivered by an air cleaner. CADR also
determines how well an air cleaner reduces pollutants such as
tobacco smoke, pollen and dust.
To help figure out what was effective,
the Association of Home Appliance Manufacturers (AHAM)
developed a method for measuring the clean air delivery rate for
portable household electric room air cleaners. The resulting
standard became an American National Standard in 1988. Known as
ANSI/AHAM AC-1, it measures the air cleaner's ability to reduce
tobacco smoke, dust and pollen particles in a room. It also includes
a method for calculating the suggested room size.
Looking at a HEPA air
cleaner that has the AHAM seal of approval is not a bad place to
start but it should not be your sole factor in determining what is a
"quality" HEPA air cleaner. The CADR test is preformed over a very
short period of time, 20 minutes, and the true test of air filter
media is how it well it performs over time. Keep these points in
mind when looking at air cleaners and the product information talks
about how well it preformed in the CADR tests.
- The CADR test
only last 20 minutes. You want your HEPA air cleaner to remove
particles quickly and to keep removing them over a very long
period of time. Almost all new air cleaners will perform well for
the first 20 minutes. For some air cleaners the filtration media
becomes more efficient over time and some becomes less efficient
with continued use.
- Many of the
air cleaners now use ionization (electrostatic charge) to remove
particles from the air. Two problems with this is that the plates or
rods used to create the charge get dirty quickly an the effency of
the air cleaner drops off rapidly. The other thing most manufactures
using this technology fail to mention is that the particles are
removed but are now attached to the surfaces in the room (ionization
makes the particles heavy so the fall out of the air) and will
become airborne once you move around the room.
- The CADR test
does not test filter efficiency. Filter efficiency is the
ratio of particles trapped by a filter over the total number of
particles found in the air upstream of the filter. A count of the
downstream particles is often used to determine the number of
particles trapped by the filter. In other words how well a
filter traps the stuff floating in the air.
- The CADR test
is a factor of air flow through the air cleaner and filtration. An
air cleaner unit with a high air flow rate and low filter efficiency
can score the same on the CADR test as a filter system with a low
air flow rate and a high filter efficiency.
- A variety of
particle sizes are used in the CADR test. Large particles such as
pollen and house dust allergens are heavy and settle out of the air
quickly. These are not the particles that cause the most problems.
Smaller particles, which are the most troublesome to health, remain
suspended in the air for longer periods. These smaller particles may
be problematic to you as they are the most difficult to dislodge
from the lungs. It is more important to be concerned with small
particle sizes. Air cleaners designed to capture small particle
sizes will also trap the larger size particles.
CADR ratings and
AHAM seals do not mean the HEPA air cleaner is bad but it does not mean
it will really do what you need it to do over the long haul
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