More Air Changes Not Always Good


One might think that rapid air changes would be a good way to dilute the SARs-CoV-2 virus and prevent its spread throughout a building. While this seems intuitive, new studies show this isn’t the case. In fact, rapid air changes spread the virus from the source at higher concentrations. Within 30 minutes of an air change, particle levels spike and stay elevated for another 90 minutes. Therefore, building managers should be aware that more air changes are not always effective in reducing virus concentrations.

No Clear Benefit to Higher Air Change Rates

Previous studies have focused on aerosol spread within a one-room building. In this case, increased ventilation reduces the concentration of the virus. However, a new study in multi-room buildings shows that air exchanges elevate virus concentration in adjoining rooms. Researchers, including HVAC experts, in the U.S. Department of Energy’s Pacific Northwest National Laboratory conducted the study. The study’s author, Leonard Pease, compared the finding to the way secondhand smoke from cigarettes reacts to air exchange. The smoke is reduced in the room where the air exchange occurs but is dispersed to adjoining rooms. The same holds true for viral transmission. While the concentration is lower, some level of risk remains.

The research team used particles similar to SARS-CoV-2 to model their spread throughout a small three-room building. The study recreated what happens to the particles after a person coughs for five minutes in one room of the building. They looked at the effects of different rates of outdoor air brought into the air supply, different filtration levels, and different air changes per hour. While the researchers found clear benefits in increasing the intake of outdoor air, the effect of more air changes was not as apparent. 

Improved Filtration vs. Higher Air Change Rate

If a higher air change rate offers no clear benefit to reducing the coronavirus, what can building engineers do to limit risk in their buildings? Strong filtration is proven effective in reducing SARS-CoV-2 transmission. The Department of Energy study found that strong filters reduce the chances for infection in the adjoining rooms of buildings. The higher the MERV rating the more pronounced the reduction. For example, a MERV-8 filter lowered the peak levels of virus particles to 20 percent. However, a MERV-13 filter brought peak concentrations down to less than one-tenth of a percent from what the MERV-8 filter delivered.

Pure Air Control Services Solutions

Building and facilities managers face many challenges in maintaining healthy buildings at any given time. In times of pandemic, those challenges increase greatly. That’s why Pure Air Control’s Building Sciences division is here to help lower the risk of virus transmission through building HVAC systems. If a higher air change rate is not effective in reducing virus concentrations improvements to ventilation are. Our building assessments and forensic investigations pinpoint problems and offer solutions. The performance of indoor environmental testing not only makes building safer but also more comfortable and energy-efficient.

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Lower Your Risk Today!

More air changes alone won’t reduce a building’s risk for virus transmission, however, expert consultation, actionable data, and professional IAQ solutions will. They improve system performance and reduce energy costs too. Contact Pure Air Control Services today. Call 1-800-422-7873 or email us here.