Assessment of HVAC Systems to Develop Recommendations
For Reducing Airborne Concentrations of Infectious Aerosols, such as the SARS-CoV-2 Virus
June 9, 2020
The Centers for Disease Control (CDC) has issued a document titled Interim Guidance for Businesses and Employers Responding to Coronavirus Disease 2019 (COVID-19), May 2020. The goal of this interim guidance is to help prevent workplace exposures to COVID-19 in non-healthcare settings. Optimizing the physical work environment and improving building ventilation are included among recommended actions to:
- Prevent and reduce transmission among employees
- Maintain healthy business operations
- Maintain a healthy work environment
SARS-CoV-2 is transmissible from asymptomatic individuals, and SARS-CoV-2 viral particles remain viable in aerosols for a period of hours.[2,3] Reducing the frequency and intensity of exposure to the virus may reduce the infectious dose and the risk of contracting disease and disease severity.[4,5] Thus, the CDC has recommended measures including social distancing, face coverings and other behavior modifications to reduce transmission.[1,6]
To help maintain a healthy environment, the interim guidance recommends considering improving the engineering controls using the building ventilation system. Per CDC guidance, this may include some or all of the following activities:
- Increase ventilation rates.
- Ensure ventilation systems operate properly and provide acceptable indoor air quality for the current occupancy level for each space.
- Increase outdoor air ventilation, using caution in highly polluted areas. With a lower occupancy level in the building, this increases the effective dilution ventilation per person.
- Disable demand-controlled ventilation (DCV).
- Further open minimum outdoor air dampers (as high as 100%) to reduce or eliminate recirculation. In mild weather, this will not affect thermal comfort or humidity. However, this may be difficult to do in cold or hot weather.
- Improve central air filtration to the MERV-13 or the highest compatible with the filter rack, and seal edges of the filter to limit bypass.
- Check filters to ensure they are within service life and appropriately installed.
- Keep systems running longer hours, 24/7 if possible, to enhance air exchanges in the building space.
The CDC interim guidance is based on recommendations from the American Society of Heating Refrigerating and Air Conditioning Engineers (ASHRAE) which has also issued several recommendations contained within the Guidance for Building Operations During the COVID-19 Pandemic and ASHRAE Position Document on Infectious Aerosols. ASHRAE has issued the following two statements regarding transmission of SARS-CoV-2 and the operation of HVAC systems during the COVID-19 pandemic:
Transmission of SARS-CoV-2 through the air is sufficiently likely that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of heating, ventilating, and air-conditioning systems, can reduce airborne exposures.
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. Unconditioned spaces can cause thermal stress to people that may be directly life threatening and that may also lower resistance to infection. In general, disabling of heating, ventilating, and air-conditioning systems is not a recommended measure to reduce the transmission of the virus.
How We Can Help
Sud Associates has over 40 years of experience identifying and implementing engineering solutions for a wide range of clients including universities, state and local government buildings, multi-use facilities, school systems, industrial facilities, as well as park and recreation facilities. We will assess your facility and develop custom solutions with the goal of reducing the risk of exposure to airborne pathogens, including the virus that causes COVID-19, by reducing their concentration. Our services begin with an assessment to determine the practicality of the generally accepted and recommended strategies for your building. For strategies that require modifications to the HVAC systems, we can provide design and construction administration services customized to your system needs.
Depending on your specific conditions and requirements, our services could be provided in the following incremental steps.
- Facility Assessment and Recommendations.
- A review of your drawings and a walk though inspection of your building.
- Interviewing the HVAC maintenance staff to understand the HVAC system and its use and capabilities.
- Interviewing key staff members to understand space use, schedule, utilization and other parameters.
- Recommendations that are primarily operational in nature and can be implemented with minor to moderate modifications to the HVAC system.
- Recommendations that are practical for the building that will require modifications to the HVAC system. Provide a budget cost estimate.
- Design and Construction Administration services for recommendations that require modifications to the HVAC system. Depending on your particular situation this could take the form of working informally with your current HVAC maintenance and controls vendors or developing formal design documents for bidding by outside contractors. The services will include Construction Management and inspections to assure proper implementation.
With 40+ years of experience in performing HVAC systems assessments and a highly qualified staff, Sud Associates. P.A. (www.sudassociates.com) is uniquely qualified to assist in tackling this new challenge. For further information, please contact:
Ish Sud, Ph.D., P.E., Fellow ASHRAE, LEED AP | President
Sud Associates, P.A., 1813 Chapel Hill Road, Durham, NC 27707 | T 919.493.5277 ||
1. Centers for Disease Control. Interim Guidance for Businesses and Employers Responding to Coronavirus Disease 2019 (COVID-19), May 2020.
2. van Doremalen, N. et al. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. New England Journal of Medicine 382, 1564–1567 (2020).
3. Gandhi, M., Yokoe, D. S. & Havlir, D. V. Asymptomatic Transmission, the Achilles’ Heel of Current Strategies to Control Covid-19. New England Journal of Medicine 382, 2158–2160 (2020).
4. Zhou, F. et al. Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study. The Lancet 395, 1054–1062 (2020).
5. He, X. et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nature Medicine 26, 672–675 (2020).
7. Schoen, L. Guidance for Building Operations During the COVID-19 Pandemic. (2020).
8. ASHRAE Board of Directors. ASHRAE Position Document on Infectious Aerosols. (2020).