HVAC systems use filters that receive a MERV (Minimum Efficiency Reporting Value) rating based on several factors, including the size and amount of Particulate Matter (PM), microscopic aerosol particles made up of solids and liquids that are able to pass through. MERV ratings range from one to sixteen, with sixteen being the best, filtering out 75 percent or more of the smaller PM that ranges from 0.3 to one micron in size. It’s important to understand PM because it plays a role in why the CDC recently changed their stance on how they believe COVID-19 is spread—not through surface contact, but rather close proximity to a carrier of the virus via droplets in the air.
Most commercial office buildings utilize MERV 6 filters which are not sufficient to filter out the COVID virus from the air. ASHRAE recommends upgrading to at least MERV 13 filters. Increasing the filter quality will result in an increase in filter pressure drop. Consulting a Licensed Professional Engineer is recommended.
If increasing the filter quality due to the physical restraints of the AHU/RTU filter box or static pressure limitations of the fans is not possible, Bi-polar ionization (BPI) is a method of air filtration that may offer a solution to better filtration. BPI filters, are relatively simple to install by just cutting a hole in the existing supply ductwork and can supplement existing filtration methodologies. BPI filter manufacturer’s tout effective protection against the flu virus. ASHRAE has not recommended BPI filtration yet because of a lack of peer reviewed research.