Indoor Air Quality (IAQ) Regarding Covid19

As we continue to navigate through the Covid-19 pandemic, we understand there are many questions about what normal looks like and what it will look like in the future.Although we don’t have the magical answer to all the questions, we do have the experience and advise around IAQ and some considerations that should be taken in your building(s).As a society we are all concerned about the possibility of transmission through the air of various pathogens.The American Society of Heating, Refrigeration, & Air Conditioning Engineers (ASHRAE) is providing guidance on the design, operation, and maintenance of HVAC systems to help reduce the dangers of pathogen transmission through the air.ASHRAE has stated, “that changes to building operations, including the operation of HVAC systems can reduce airborne exposures.Disabling of HVAC systems is not a recommended measure to reduce the transmission of the virus.”1

The World Health Organization has confirmed that COVID-19 survives under certain indoor air conditions.2Air humidification levels impact viruses.Dry indoor air has been associated with higher rates of infectious and inflammatory diseases in building occupants.2 Dr. Stephanie Taylor, M.D., M. Arch, CIC, of Harvard Medical School has indicated that there is an abundance of data which indicates indoor relative humidity levels between 40-60% benefit building occupants by2:

  • Infectious aerosols released from a sick person settle out of the air quickly and they can be wiped away from surfaces.
  • Viruses and bacteria carried in droplets are less infectious within this relative humidity range.
  • Our immune systems are optimized to fight viral and bacterial infections within this relative humidity range.

Airflow patterns, HVAC Systems, and local exhaust ventilation (LEV) systems can be designed and operated to provide dilution, pressurization, temperature and humidity control, and filtration controls to reduce building occupant exposures to infectious aerosols.ASHRAE’s policy positions are based upon adoption of the Agency for Healthcare Research and Quality (AHRQ) rubric for expressing the scientific certainty behind their recommendations.Evidence levels utilize a grade of A, B, C, D, or E with a grade A indicating strongly recommended, good evidence; and a grade of E indicating evidence is insufficient, lacking, or of poor quality to determine the benefits and harm.Changes to building HVAC operations can reduce airborne exposures, and HVAC system ventilation and filtration can reduce airborne concentration of SARS-CoV-2.3 Dilution and extraction ventilation, pressurization, airflow distribution and optimization, mechanical filtration, ultraviolet germicidal irradiation (UVGI) and humidity control are effective strategies for reducing the risk of dissemination of infectious aerosols in buildings.3 ASHRAE recommended HVAC strategies with an evidence level grade of A or B include the following3:

  • Enhanced filtration in occupant dense and/or higher risk spaces
  • Upper room UVGI to supplement supply airflow
  • Local exhaust ventilation for source control
  • Personalized ventilation systems for high risk tasks
  • Portable free-standing room air cleaners with HEPA filters
  • Temperature and humidity control

ASHRAE Epidemic Task Force chair and 2013-14 ASHRAE President Bill Bahnfleth said, “Key elements of a strategy to limit the spread of the COVID-19 virus are to perform needed heating, ventilating, and air conditioning (HVAC) system maintenance, including filter changes, and to run HVAC equipment, prior to re-occupancy.”4

ASHRAE recommendations for building readiness and reopening buildings include4:

  • Creating a strategic plan prior to opening a building.The plan should include measures to make occupants feel safer, ensuring supply chain for critical items (ie, filters, belts, etc.) and communication plans for building support and safety measures for occupants.
  • Provide outdoor air building flushing two hours before and post occupancy.This should include opening outside air dampers and/or windows (where ambient conditions and equipment capacities permit), and operating exhaust fans.
  • Operate the HVAC system on minimum outside air when the building is unoccupied.
  • Operate garage exhaust fans two hours prior to garage occupancy.
  • Ensure custodial cleaning procedures follow EPA and CDC guidelines regarding approved prodcuts and methods.In particular, disinfect high touch areas (ie, light switches, thermostats, door handles, etc.) and the interior of refrigeration equipment (ie, refrigerators, electric water coolers, etc.) where viruses can potentially survive for long periods of time.

The measures noted herein improve indoor air quality and reduce the dangers of pathogen transmission through the air and result in a reduction in airborne exposures.We would be glad to discuss, review, and assist you in evaluating your HVAC system for indoor air quality improvement opportunities.

Please contact your trusted Pueblo representative or contact Steve O’Brien Pueblo’s professional engineer for more information regarding these considerations.

Pueblo Mechanical & Controls

Steve O’Brien, P.E

Cell: 480-745-4169


1 Environmental Health Committee (EHC) Emerging Issue Brief, “Pandemic COVID-19 and Airborne Transmission”

2 PBC Today Article dated April 14, 2020, titled “Indoor Humidity Regulations Will Reduce Burden of COVID-19”

3 ASHRAE Position Document on Infectious Aerosols dated April 14, 2020

4 ASHRAE Press Release dated May 7, 2020, titled “ASHRAE Offers COVID-19 Building Readiness/Reopening Guidance”