Oct 29, 2020

Airports grappling with the pervasive impacts of COVID-19 are investigating ways to stem the transmission of the virus, convince passengers that it is safe to fly again and shield airport passengers and staff from future pathogens as well.

HVAC systems, in particular, play a critical role in overall indoor air quality and in preventing the transmission of contagious illnesses, including SARS-CoV-2, the virus that causes COVID-19. A properly functioning HVAC system can reduce the risk of transmission of SARS-CoV-2 and other viruses and bacteria, as well as unhealthy CO2 and particulates. While the matter remains controversial, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), an industry think-tank, has said that transmission of SARS-CoV-2 through the air is “sufficiently likely.”

Brian Phillips, PE,
LEED® AP

Vice President, Aviation

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HVAC systems, in particular, play a critical role in overall indoor air quality and in preventing the transmission of contagious illnesses

“Ventilation and filtration provided by heating, ventilating, and air conditioning systems can reduce the airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air,” ASHRAE said in an April 20 statement.

Ventilation—the introduction of fresh outside air into a space such as an airport—can reduce contaminants by exhausting some of the existing air from the space and replacing it with fresh air. Facilities such as airports often base the percentage of fresh air intake on the number of occupants.

The season and outside temperatures also play a large part in how much fresh air can be introduced. During certain seasons and in certain locations, facilities can use up to 100 percent fresh air to cool their spaces, relying on a process called the “economizer cycle.”

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“…most HVAC systems are preset to take in specific percentages of fresh air…tweaks can be made to maximize systems’ ability to operate…”

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While most HVAC systems are preset to take in specific percentages of fresh air, and increasing those percentages can be problematic, some tweaks still can be made to maximize systems’ ability to operate in economizer cycles. Ensuring that air handling units are operating properly, that air dampers are open to at least the minimum setting, and that economizer mode is working properly all can help improve ventilation.

There are many types of air filtration technologies available, and their use depends largely on the type of building and its intended use. Most airports use multi-stage, pleated cartridge particulate filters, sometimes in combination with a more advanced air filtration technology.

A filter’s efficiency is measured by the size of microns it captures, ranging from 0.3 to 10 microns, and filters are rated by their Minimum Efficiency Reporting Values, or MERVs. The higher the MERV rating, the smaller the particles a filter can trap. Surgical or “clean” rooms, for example, use filters with a MERV rating of 17 to 20 which are also referred to as High Efficiency Particulate Air (HEPA) filters. Filters with a MERV rating ranging from 8 to 16 are prescribed for other hospital settings, as well as for residential and commercial applications, including airports.

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Using filters with a higher MERV rating may seem like a simple fix, but it often isn’t. As with air intake, HVAC systems are designed to be used in conjunction with specific types of filters, and using filters above a 16 MERV rating isn’t recommended for most. In fact, using the wrong filter can harm or compromise the system and sharply escalate operating costs. Instead, airports should consider only incremental improvements in filtration, swapping out MERV 13 filters with MERV 16s, for example. This shouldn’t be done, however, without an engineering analysis to determine if the upgrade will degrade the performance of the system and its air handling units.

Adding a second form of filtration also could be helpful, and airports should consider using a pre-filter rated at MERV 8, along with final filtration rated at MERV 13 to 16.  Bipolar ionization or ultra-violet light technology, for example, can be retrofitted to existing air handling units to improve filtration, although the costs may be prohibitive and should be carefully considered.  These advanced technologies make more sense in new HVAC systems.  Other new but less-proven filter technologies are being offered as well, but require careful analysis to determine effectiveness as well as understand potential drawbacks.

Airports can maximize filtrations systems’ efficiency by enacting a rigorous, consistent maintenance and replacement schedule. Particulate filters should be replaced every three months. More advanced filtration technologies need to be maintained according to manufacturer recommendations. Because of the threat of contagion, maintenance workers should appropriate personal protective equipment (PPE), including gloves and masks.

While the issue of transmission of SARS-CoV-2 through airports’ HVAC systems is far from clear and needs more study, prudent airports can take discernable steps now to keep their facilities safe as the pandemic continues to evolve. And, improvements made now can help airports better prepare for and prevent the spread of future contagious epidemics.