Just where does dust trails on the ceiling come from? The short answer; according to ASHRAE the dust on the ceiling is formed by dust in the occupied space, air filters have no effect on the dust trails.
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 Value air filters can be used in almost any application to improve equipment performance or just to improve Indoor Air Quality.
Submitted by Mack Barnhardt
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