Using MERV 13+ Filters May Minimize Virus Spread

Filtration traps particulates, which plays a key role in helping minimize the spread of the virus to areas of the building served by the HVAC system and ductwork. Research shows that the particle size of SARS-CoV-2 is approximately 0.1 micrometer (µm). However, the virus particles are human-generated, and when exhaled, the virus will be attached to the respiratory droplets that are larger than the individual virus. Most respiratory droplets and particles that exhaled are 1 µm in size or larger. 

HVAC Filter Considerations

ASHRAE recommends a filter efficiency of MERV 13 or higher provided that it does not affect the performance of the HVAC system or occupant comfort.  The Minimum Efficiency Reporting Value (MERV) scale ranges from 1, the least efficient, to 16, the most efficient, and measures a filter’s ability to remove or trap particles from .3 to 10 microns in size from the airstream.

•    MERV 13 filter - is at least 85% efficient at capturing particles in the 1 µm to 3 µm size range.
•    MERV 14 filter - is at least 90% efficient at capturing particles in the 1 µm to 3 µm size range.

To be effective, filters need to be installed so that all the air goes through the filter and not around it. If there are gaps between the filter and the frame or if it is not sized properly, air will travel the path of least resistance and bypass the filter media and not be cleaned.  If the filters seem to be loose in their frames, then gasketing material can be used to provide a tighter fit.

Filter upgrades can impact HVAC system performance and retaining the services of a certified commissioning provider (CxP) or testing, adjusting and balancing (TAB) service is highly recommended.

•    Higher efficient filters may have an increased pressure drop over currently installed filters
•    The HVAC systems supply fan must be able to overcome the additional filter resistance in order to deliver design airflow

Before upgrading to a higher efficient filter, a certified professional will perform base line testing or evaluation of what is currently installed to determine how things are working now.  This includes reviewing the last balancing report, testing airflows and pressures as currently installed and reviewing fan performance data to determine a performance profile.  This could include a performance profile if the current filter installation is dirty and then repeating with clean filters.

The proposed higher efficiency filter pressure drop can be tested on the existing filter setup by blocking off portions of the current filter to mimic the increased filter resistance.  Measurements of static pressure, filter differential pressure and performing a duct traverse of the main supply air flow will help to determine if the current system fans can handle the increased load and deliver building design flows and provide occupant comfort.

If the current setup is insufficient, then the certified professional can evaluate the fan drive to determine if the fan speed can be increased to overcome the added resistance or to provide guidance and suggestions for alternate solutions.
 

Trust TSI Instrumentation

Be sure to work with a Testing, Adjusting, Balancing (TAB) professional and invest in reliable instrumentation to help keep your building occupants safe.