Layered Ventilation Strategies for Commercial and Public Spaces

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Since the onset of the COVID-19 pandemic, public indoor spaces have become a health hazard because the virus spreads through airborne particles and droplets. When COVID-19 positive people exhale, the infectious droplets are released into the air and transmittable from person to person. In indoor spaces, these particles spread through the room and continue to accumulate, making public indoor spaces especially risky. Congregating in outdoor areas is safer than gathering in indoor spaces.

However, there are many instances where congregation outside is not an option, such as for education and healthcare purposes. Various precautions must be taken inside these buildings to lower the risk of virus transmission in these cases. The U.S. Center for Disease Control (CDC) provides guidance that higher education and healthcare administrators can use to prevent the transmission of SARS-CoV-2 among students, faculty, staff, and patients.

Maximizing Safety in Public Indoor Spaces with a Layered Approach

As of May 23, 2022, The CDC recommends a layered approach to reduce transmission of the COVID-19 causing virus. This multifaceted method instructs individuals to wear face masks, socially distance themselves from others, avoid crowded indoor spaces, maintain proper hand hygiene, and receive a COVID-19 vaccination. Additionally, the layered approach suggests that engineering controls be updated, as improvements to building ventilation and filtration will help mitigate the spread of disease and lower the risk of exposure.


Upgrading and Improving Engineering Controls to Reduce Transmission

The engineering controls vary depending on the type of structure and the building’s air handling units. Still, the following set of general guidelines can be used to adjust the air handling strategies in commercial buildings. While an establishment may have had code-compliant indoor air quality before the onset of the pandemic, it should still be updated and improved to compensate for the increase in infectious air particles.

Generally, the air filtration can be improved, outside-air ventilation should be increased, and airflow can be reconfigured to lessen the indoor airborne transmission of the virus between people.


Choosing Air Filters and Cleaners

AHU filters and other air cleaners can lessen the number of contaminants in the air, including airborne particles containing SARS-CoV-2. Therefore, the air that is re-circulated through a building and potentially contains the virus should be more vigorously filtered to remove as many infected air particles as possible. This may involve portable air cleaners and upgrading HVAC filters to MERV 13 or higher or a HEPA Filter, depending on the blueprint and intended usage of the space.

An air cleaner must be able to remove small airborne particles ranging from 0.1-1 um for it to be effective. When searching for the proper air cleaner, pay attention to how manufacturers advertise their product’s capabilities.

For example, it may be reported as something along the lines of “removes 99% of particles as small as 0.2 um”. Additionally, the Clean Air Delivery Rate (CADR) rating system and Minimum Efficiency Reporting Value (MERV) are used by many manufacturers. The fraction of particles removed by a filter is called filter efficiency. MERC ranges from 1 to 16, and the higher the MERV, the higher the filter efficiency. MERV 13 or higher are capable of eliminating airborne particles containing viruses. Other manufacturers report using High-Efficiency Particulate Air (HEPA) filters, which effectively remove small particles. HEPA filters are more efficient than MERV 16 filters.

To choose an air cleaner that will work for your needs, Kevin Clare, a sales engineer at Coward Environmental, suggests,

“First, find a unit that indicates that it filters particles in the 0.1-1 um range is a MERV 13 or higher, or a HEPA unit. The unit should also have a high CADR for smoke. And lastly, ensure that the unit is the right size for the space it will be used in.”

In high-risk areas in healthcare facilities occupied by patients with COVID-19, supplementing existing systems with portable HEPA fans and filtration systems can enhance air cleaning.

Clare adds, “Make sure existing units are within their recommended service life and adequately sized. In addition, filter housing and racks should be inspected to ensure proper fit and lessen the airflow around (instead of through) the filter.

“Additionally, other technologies such as ionization should be considered to proactively deactivate pathogens in the occupied space.” Clare emphasizes,  “Ionization has also demonstrated effectiveness in reducing airborne particulate matter in that critical 0.1-1 um range.”

Increasing Outside Air and Reconfiguring Airflow

In addition to updating air filtration, the introduction of outside air should be increased. Clare suggests, “Open outdoor air dampers beyond minimum settings to reduce the amount of air recirculation. This should not affect thermal comfort or humidity in mild weather, but may in cold, hot, or humid weather, possibly requiring consultation with an airflow professional.”

When weather conditions allow, outdoor airflow can be increased by simply opening windows and doors. Ensure that the occupants’ safety and health risks, such as asthma, are assessed before doing so. Fans can be utilized to increase the effectiveness of open windows by evaluating the configuration of a room. Fans should not be placed in a way that can cause infectious particles to flow directly from person to person. A window fan can draw air from indoors to outdoors without creating air currents inside the room. In larger facilities, gable fans and roof ventilators can be used to achieve this.

Clean-to-less-clean airflow can be configured by adjusting exhaust air grilles, the supply louvers, and damper settings. This airflow method is easier to accomplish when a ceiling grid system contains the supply and exhaust points.

To update ventilation systems, first, ensure that they are operating correctly and providing the right indoor air quality for the rate of occupancy. Clare notes, “Air handling units can be adjusted to increase the total airflow to occupied spaces, and any demand-controlled ventilation (DCV) controls that reduce air supply should be turned off. In addition, exhaust fans in restrooms and food service areas should be inspected to ensure they are fully functional and operating at full capacity when these spaces are occupied.”

The Layered Approach Reduces Likelihood of Transmission

Air handling and ventilation are critical elements in the fight to reduce the spread of COVID and other airborne diseases. Employing as many of these methods as possible will help healthcare, businesses, and public spaces to decrease the transmission of the airborne SARS-CoV-2 virus, keeping occupants as safe as possible.