SARS-CoV-2 the source of COVID-19 is an airborne virus that can infect people that breath in a quantity of the contaminated aerosol. Aerosolized means that the virus, that is a very small 0.12 microns, is encapsulated in respiratory droplets of various sizes up to 100 microns. Larger droplets fall out of the air and smaller ones, typically less than 10 microns, can stay in the air for long periods (several hours) and cover much larger distances than 6 ft. As the respiratory fluid encapsulating one or more virus particles is evaporated by dry air, the time and distance it may remain buoyant increases. These aerosols can move around objects, such as plexiglass partitions, by following the current of the air created by the HVAC system, room fans and filters, movement of people, and buoyancy caused by body heat. Seasonal influenza is of similar size and behaves in a similar way.
CDC states: Ventilation is one component of maintaining healthy environments, and is an important COVID-19 prevention strategy for schools and childcare programs and to ensure ventilation systems operate properly and provide acceptable indoor air quality for the current occupancy level for each space.
Protective ventilation practices and interventions can reduce the airborne concentrations and reduce the overall viral dose to occupants. Ventilation system upgrades or improvements can increase the delivery of clean air and dilute potential contaminants.
Dilution and filtration of aerosol viruses has long been a control method. In the beginning of COVID-19 it wasn’t widely understood that this virus was airborne. ASHRAE and some aerosol scientists saw the threat early on and promoted enhanced ventilation and filtration to make indoors safer. It is also reccomended to disable demand control ventilation (DCV), which may reduce ventilation rates. The CDC now has clear guidance that ventilation is important for schools not only for COVID-19 but for healthier schools in general. A recent scientific study shows that improved ventilation lowered the risk of COVID-19 transmission in schools by 39%, and combined with filtration lowered the risk by 48%. Ventilation is also important to reduce concentrations of off-gassed byproducts used to clean surfaces. For ventilation to be effective and not to cause unintended problems, the building exhaust systems should be modified along with, and controlled in sequence with, ventilation to ensure proper room air changes, directional flow, and pressurization.
FUTURE PROOF K-12 SCHOOLS
A report from Johns Hopkins Center for Health Security states “ventilation improvements are a cost-effective public health measure“. The expert panel recommends the improving and upgrading mechanical ventilation in schools as a priority that will have benefits that will outlast the COVID-19 pandemic. It further states that “It is a general principle of management that recommendations are far more likely to be effective if they are being monitored and enforced in real time“. In simple terms, you cannot control what you do not measure. Active airflow measurement to determine classroom ventilation is the only ongoing way to verify that you have ventilation airflow rates that meet or exceed building codes. In-room sensors are a proxy and only provide an indication, not a true validation. A one time airflow balance although important, is a snapshot in time and subject to external forces that can change airflows over time, and will not be noticed if not actively monitored.
MAINTAINING CONTROL = HEALTHIER INDOORS
Airflow measuring stations integrated into a building automation system allow for automatic adjustments to ventilation rates as equipment or conditions degrade or change. It will also ensure the building is prepared in future if there is a need to increase and verify the ventilation rates. Ventilation and building airflow control isn’t limited to COVID-19, it applies to any potential indoor contaminant. Maintaining proper outdoor air ventilation is essential for reducing indoor pollution concentration. Maintaining proper building pressurization will ensure that the air coming into the building, comes in through the HVAC system where it can be properly filtered and be sure it is outdoor fresh. Uncontrolled or imbalanced airflow, may result in air entering the space from undesired locations such as, through walls, windows, and doors; from janitor closets or mechanical rooms; from toilet or locker rooms; from basements or underground. The air from these spaces are contaminated when compared to other spaces and are normally exhausted, but due to an imbalance can bring in pollutants. Measuring and controlling airflow rates, filtration, and source control are necessary components for maintain healthy schools to ensure student health and that of school professionals. Learn more about Ebtron Solutions for Schools.
The Elementary and Secondary School Emergency Relief Fund (ESSERII) and the American Rescue Plan Act of 2021 allows for LEAs to use available funds for improvements, repairs, and upgrades to mechanical ventilation and control systems. Ventilation is known to make indoors safer from airborne viruses.
Additional Resources Related to Protecting Schools from COVID-19
The potential for airborne dissemination of infectious pathogens is widely recognized. Building science professionals must recognize the importance of facility operations and ventilation systems in interrupting disease transmission. 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 and transportation environments.
ASHRAE Position Document on Infectious Aerosols
• READ: ASHRAE Position Documents
A safe and healthy building is dependent on dilution ventilation and maintaining proper pressurization. Unless the rate of outdoor airflow is actively measured, determining under-ventilation may only come after it is too late to prevent the outcome.
The Importance of Measuring and Controlling Ventilation
Center for Green Schools
Indoor air pollution is often greater than outdoor levels of air pollution due to a general lack of adequate air filtration and ventilation