Air Filtration Affects More than the Air You Breathe
Published by MED Magazine
Indoor air quality and efficiently running HVAC equipment is Tyler Pierce’s main focus when talking to facilities about filtration. Pierce has been with O'Connor Company, a division of HVAC Elements, for 15 years. As manager of the aftermarket parts department for the last ten years, Pierce oversees replacement parts and filters for equipment provided by HVAC Elements.
Pierce knows filtration is key for keeping equipment clean which will maintain its operating efficiency as well as provide exceptional indoor air quality. "Some people just look at a filter as something they have to change periodically," says Pierce. "They may not give much thought as to what that filter actually does for air quality or how it protects the equipment it serves."
Inexpensive filters, what Pierce calls “fly and moth catchers,” have no trouble catching larger particulates. But Pierce says it is the fine particulates that do the most damage to long-term equipment operation and immediately compromise indoor air quality.
Understanding MERV Ratings
Most healthcare facilities use a series of filters together to ensure they are catching as many particulates as possible. Each filter carries a MERV rating, or Minimum Efficiency Reporting Value. The higher the MERV rating, the greater percentage of fine particulates the filter will remove from the air. For example, a hospital's air handler might use a pre-filter with a MERV of 8, a second stage filter with a MERV of 11, and a final filter that is a MERV 15 or a High Efficiency Particulate Air (HEPA) filter. Enhancing the efficiency of any filter will enhance the longevity of each subsequent filter in the airstream.
"The MERV ratings of filters are driven by the environment you are serving," explains Pierce. "In a surgery application for instance, you would not use the kind of filter you might use in your home. You want the cleanest air possible."
While it is common for hospitals to use a MERV 14 or HEPA rated final filter, clinics and other outpatient facilities often do not use filters that high. But now, in the era of COVID, Pierce says organizations such as the CDC and ASHRAE recommend all commercial buildings use the highest efficiency filters possible without having detrimental effects on overall HVAC system performance – ideally a minimum of MERV 13.
"If you look at a standard MERV 8 filter, it is 30 to 35 percent efficient at removing particulates 3 to 10 microns in size," says Pierce. "If you move up to a MERV 13, it is 89 to 90 percent efficient at removing particulates that are 0.3 microns to 1 micron. So you're more efficient at removing both the finer and larger particulates using a MERV 13 than a MERV 8 filter."
For reference, a human hair is about 70 microns (+/- 20) in diameter, and a human red blood cell is about 5 microns in diameter. Particulates trapped in high efficiency air filters are much smaller – often as small as 0.3 microns in size.
Improved Efficiency = Lower Cost & Better Air
The main benefit of efficient filtration is dust reduction and improved air quality. But that is not the only consideration for healthcare facilities when it comes to filter selection. Cost savings via increased equipment efficiency are often an overlooked benefit.
Filters with a higher MERV rating also maintain the designed efficiency of the entire air handling system by reducing dust particle collection on the heating or cooling coil. Dirty coils decrease the unit’s efficiency and cost more to operate in the long run. "There have been studies done that .006 inch of dust on a heating or cooling coil can reduce your heating or cooling efficiency by up to 30 percent," says Pierce.
New Technology for Improved Air Quality
Many virus particles, including COVID-19 which range in size from 0.1 to as little as 0.01 microns, cannot be completely filtered out by high rated MERV or HEPA filters. That is where the addition of needlepoint bipolar ionization (NPBI) systems can be invaluable.
NPBI causes particles too small for standard filters to agglomerate, or get larger, and allow the particles to settle out of the airspace or travel to the return air duct bringing the particles back to the pre-filter to be filtered out.
As an example, Pierce says a MERV 8 filter by itself is only about 11 percent efficient at catching sub-micron particles. With the addition of NPBI, that jumps to 84 percent. While ionization systems have been in use for years, recent improvements allow this technology to be more cost effective and produce no off-gassing.
Pierce recommended a few filtration best practices to keep systems running optimally. In addition to changing filters regularly, taping the seams of filters in a filter bank forces air through the filters and prevents any air bypass between filters. Installing gaskets on the inside wall where the filter meets the unit as well as on the entry door of the air handler or roof top ensures a tight seal and prevents additional air bypass.
When it comes to the value that proper filter selection brings, Pierce says "The bottom line is the more efficient your filter, the cleaner your air, the better your equipment will perform, and the better the overall indoor air quality will be for the people occupying the space."