Even if you had the best or the worst filter in your HVAC system dust trails would still appear. Why, because the occupied area where the supply vents are located is where the dust is created or introduced into the air system. According to Science News (April 1, 2005), "The most common types of aerosols are soot, ash and other man-made particles as well as naturally derived dust and salt. Until now, plants and animals have been considered just a small source of particulate pollution. But a new study suggests that up to 25 percent of aerosols worldwide could be coming from biological sources, including fur, skin, pollen and bacteria". Dust trails can be controlled! To
control dust trails we need to understand how dust trails are
formed, how dust is introduced into the air, how it forms on the
ceiling &
how we can control it.
 Dust
is more then what Science News as stated above, we can add insects,
paper,
carpet, rubber from tires, clothes, space dust and the list goes on. On
average
98% of the dust in the air is under 5-microns by particle count, but
only
represents less than 6% in particle weight and can be as small as 0.001
microns. The dust machine, everything that contributes, never stops.
This is
why most buildings will have dust issues after only 4 to 5 years of
being open if you do nothing to control dust.
How Dust Trails are Formed Dust
Trails are formed by micro-dust and large low weight dust that
is forced by the airstream of the
supply vents to stick to ceiling surface. As the particles build up and
fill
the voids in the ceiling they are forced to follow the air stream
causing the
dust trail.
 Controlling Dust Trails Keeping
in mind that dust
can be as small as 0.001-microns (see photos below), the more saturated
the occupied space is of dust the faster and bigger the dust trails
will form.
By reducing the occupied space dust load we can control how fast or how
big
dust trails will form. To accomplish this, dust is removed faster then
what you
are introducing it into the occupied space. This can be done by
manually removing
the dust by wiping, vacuuming surfaces and by filtration.
Manually
Controlling Dust
It takes a lot of labor with high cost to control dust with labor. By using products like dust sweepers that hold dust without releasing them to HEPA vacuums we can control the dust loads in our buildings The goal is to remove dust below the saturation levels on a regular schedule. Filtration to Control Dust: Filtration
can save
hundreds of dollars in labor cost to control dust in your occupied
space if the
correct air filter is used! Since dust can be 0.001 to 10 microns your
current
air filters may not be what you require for dust control? If we took
99% of
these particles that we cannot see and add them together, we have
dust.
A simple test; blow on the dust on your desk. While it was there, the dust was very visible. Once airborne, the dust breaks apart and becomes invisible, for the most part. ASHRAE 52 gives us the opportunity to control dust by focusing on the MERV Value of three particle range sizes. Using ASHRAE 52.1 & 52.2 to Control Dust ASHRAE 52.1; measures by weight and also shows the "Average Over All Efficiency" of an air filter using percentage on a light scale. If the report shows a 40% air filter, then simple reasoning will also point out that 60% is still going thru the filter media. ASHRAE
52.2; measures the particles going thru the air filter
using a laser particle counter. The 52.2
test reports the "Minimum Efficiency" and records what happens during
the lab test filter service life, hence why we have the "MERV
Value” (Minimum
Efficiency Reporting Value). Don't take
the MERV Value too seriously! After all it is only the beginning value,
not the
full performance of the air filter and is not performed in real world
applications but tested in a lab in controlled conditions that do not
equal
“Real World Conditions”.
Since
air filters
efficiency is based on overall efficiency, what does not stay in the
filter
goes thru and becomes accumulative dust to feed your dust trails. For
example,
a pleated filter may well remove just about all the particles larger
than 5
microns in size. This could be expressed as above 80-90% removal of
dust, by
weight. As the chart show (above), particles larger than 5 microns
account for only
0.18% of the total number of particles in the air, even in our Las
Vegas desert
air! Those 80-90% figures sounds impressive, but look at the numbers
and you'll
see that it still leaves over 99% of the particles (by count) that
pleats are
not filtering very well!
Another
point, ASHRAE will tape the filter in place to
prevent any bypass so to get a true reading of filter blow thru, it
will stand
to reason that if our filters are not sealed in our filter tracks then
we are
not receiving the full “Value” of the ASHRAE tested
air filter.
Another
option you should consider is what type of media to
control micro-dust on the higher MERV filters? Synthetics that depend
on static
to hold dust for higher MERV values do not do well in real
world testing,
they release dust loads as they are in service because they cannot hold
the
media static. Hybrid
Media’s rely on old fashion mechanical filtration
principles & will not degrade in efficiency. Real world 52.2
testing has
shown these Hybrid Media’s can hold its very fine dust loads.
We
offer no cost IAQ evaluations to improve your Indoor Air Quality. Air
Filtration Systems tries to go further to show you how effectively our
self-sealing, depth-loading and Hybrid media air filters can remove the
very
fine particles that become dust to keep your coils clean and improve
your air
quality. Even if you’re HVAC does not allow the use of bags
or is old and
cannot handle any extra static, with today’s filtration
technology the higher
MERV rated filters can be used in almost any application to improve
equipment
performance or just to improve Indoor Air Quality.
Submitted by Mack Barnhardt Do you have an article you would like to submit or a question you need an answer on? Contact us. |
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