CDC – Building Ventilation Target to Prevent COVID-19 Spread – May 23

Link to CDC Recommendations

  • Aim for 5 Aim to deliver 5 or more air changes per hour (ACH) of clean air to rooms in your building. This will help reduce the number of viral particles in the air. You may need to use a combination of ventilation (air supply, filtration, and air treatment) strategies to reach this target.
  • Upgrade filters Use filters rated MERV-13 or higher, when possible. Using higher-rated filters in your heating or air conditioning system can remove more germs in the air than lower-rated filters.
  • Turn your HVAC system “ON”
    Set your ventilation system to circulate more air when people are in the building. You can do this by setting the thermostat’s fan control to the “ON” position instead of “AUTO.” This will make the fan operate continuously but can increase fan energy use, so limit use to when needed.
  • Add fresh air Bring more clean outdoor air into spaces by opening windows and doors and using exhaust fans. Even small openings can help.
  • Use air cleaners Air cleaners (also known as air purifiers) filter air with high-efficiency filters that remove germs from the air. Choose one that’s the right size for your space.
  • Install UV air treatment systems UV air treatment systems can kill germs in the air. They can also provide a high level of effective air changes per hour while using little energy.
  • Use portable carbon dioxide (CO2) monitors A portable CO2 monitor can help you determine how stale or fresh the air is in rooms. Readings above 800 parts per million (ppm) suggest that you may need to bring more fresh, outdoor air into the space.

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Dr Richard Corsi – “It’s a good start and should decrease inhalation dose of respiratory aerosol concentrations by between about 20% to 40% in many classrooms (based on my experience w/ typical starting points in schools –some w/ recirculation through MERV-13 filters already achieve 5 eACH).” “Importantly, it is NOT difficult to achieve MUCH higher than 5 ACH in classrooms – even approaching 10 equivalent ACH w/ ASHRAE 62.1 ventilation + a #CorsiRosenthalBox, or 6 ACH w/ 62.1 in a typical classroom & a good HEPA air cleaner.”

“NIOSH reports 12.4 eACH on top of typical classroom ventilation with 2 CR (CorsiRosenthal DIY Boxes) in a classroom. That will often lead to 15+ eACH, pushing 80% reduction in inhalation dose of respiratory aerosol particles in tytpical classrooms w/ unit ventilation.”

“In my opinion, I would treat 5 equivalent ACH as a MINIMUM value (if not already there school districts are doing a disservice). 20 to 40% reduction in inhalation dose is better than 0%. 80% reduction in inhalation dose is better than 20 to 40%.”

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