By: Tony Fedel, Kimberly-Clark Professional Partnership Products |
When it comes to good indoor air quality, the dust and particles you don’t see are more important – and more dangerous – than the dust and particles you do see. That’s because those tiny, submicron particles are the ones that can travel to the deepest part of the lungs, where they can cause a variety of respiratory problems and other health and productivity issues.
It’s been estimated that the average human breathes in about 3,000 gallons of air each day. But what’s in that air we breathe?
The air contains bits of particulate matter – some of which is 100 times thinner than the diameter of a human hair – that are breathed into the respiratory system, where they can stick to the sides of the airway or travel deeper into the lungs. Lung-damaging dust can be as small as 0.5 microns, and airborne bacteria can be as small as 0.3 microns.
Trapping Submicron Particles
An effective air filtration strategy can defend building occupants against submicron airborne particles, but only if the air filters are chosen with care.
The filter selection process typically starts by looking at a filter’s Minimum Efficiency Reporting Value (MERV). A MERV of 1 is considered least efficient while a MERV of 16 is most efficient.
But more important than the single MERV value is the ability of the filter to trap and eliminate submicron particles. Read the entire ASHRAE 52.2 test report to find the efficiency of the filter over all three particle size ranges:
- E1 - very fine particles in the 0.3 to 1.0 micron range
- E2 - fine particles in the 1.0 to 3.0 micron range
- E3 - coarse particles in the 3.0 to 10.0 micron range
The Power of Electret Filters
When it comes to trapping submicron particles, it's a good idea to purchase filters that use electret media. That is because, while submicron particles are much smaller than the void spaces present in most commercial mechano-electret media, the electrostatic forces within the media structure allow those particles to be removed with high efficiency.
Be aware that many pleated filters have low E1 and E2 efficiencies, especially at commonly used MERV 8. In fact, under ASHRAE 52.2, filters in the MERV 1-12 range aren’t even required to be measured for E1 efficiencies, and filters in the MERV 1-8 range aren’t required to be measured for E2 efficiencies. It is therefore possible to have a MERV 8 mechano-electret media filter with better E1 particle capture than a MERV 11 mechanical-only filter.
Improving IAQ: Look Beyond MERV
High E1 and E2 efficiencies are critical for providing for good IAQ, which helps students improve learning and helps commercial and institutional building occupants avoid illness and the many costs associated with employee productivity losses. In fact, studies have found that work performance can improve by as much as 16 percent when indoor pollutant sources are removed.
Given the importance of capturing submicron particles, it’s best to look beyond MERV and focus on the filter’s efficiency removing E1 and E2 particles.