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The Clean Air Delivery Rate Standard Test
- The Clean Air
Delivery Rate Standard Test
-
- The Clean Air
Delivery Rate test, called the CADR test, is performed in a
controlled test chamber by subjecting room air filter units to various
particles which range in size from .09 microns to 11 microns which
represent tobacco smoke, pollen and dust. Overall particle
concentrations are measured in the test chamber at 2 minute intervals
for a total of 20 minutes and a general removal rate is determined for
each test product. Use of the CADR test to evaluate air cleaner
performance is not recommended.
- Test
Duration
- The
true test of air filter media is how it performs over time. Most high
quality air filter systems are designed to last 2-5 years before
requiring filter replacement. The CADR test takes a brief (20 minute)
snapshot of filter performance when an air cleaner is new. Some
filtration media become more efficient over time and some filtration
media become less efficient with continued use. The brief test period
of the CADR test does not indicate the performance of a system over
time which can be significantly different than when the product is
new. Here are two examples.
-
-
Poorly designed HEPA
air cleaners may perform well when new, but as the HEPA filters
get particle build-up, the static pressure of air trying to go
through the filter increases. Air will travel in the direction
of least resistance, causing air to bypass the filter and
release particles back into the room air.
-
Some air cleaners use technology
with electrostatic charges to attract and capture particles. As
particles cover the charged filter media or plates, this
electrostatic charge will diminish rapidly and particles will no
longer be attracted to the particle capturing mechanism. These
types of air cleaners lose substantial efficiency quickly.
- Filter
Efficiency
- The CADR test does not test filter efficiency. This 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. Both scenarios are not acceptable. The efficiency of an air cleaner system at
removing a particular particle size is unknown with the CADR test.
Considering that 90% of all particles are below 0.3 microns, which
are the most troublesome to health, it is important to know the
system efficiency of an air cleaner at trapping sub-micron
particles.
- Particle
Sizes
- 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. Smaller particles remain suspended in the air for
longer periods. These smaller particles may be problematic to
individuals as they are the most difficult to dislodge from the lungs.
Most new air filter systems can trap larger particles used in the CADR
test, especially during the short 20 minute test period. It is
more important to be concerned with low particle sizes. Air cleaner
systems designed to capture low particle sizes will also trap larger
size particles.
- Air Cleaner
Type
- The CADR test does not distinguish how particles are removed
from the air. Some air cleaning technologies, such as
Ionization, do not capture particles at all, they create an
electrostatic charge on the particle so they are attracted to
surfaces in a room. The CADR test will show that particles are
removed from the air when in fact they are deposited on surfaces
throughout a room. The CADR test does not test the
effectiveness of gaseous pollutant and odor removal. Most CADR
rated air cleaners do not effectively reduce gaseous pollutants
and odors.
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