CLEARING THE AIR

Despite the recent progress made in the fight against COVID-19 in the U.S. thanks to rising vaccination levels, the pandemic is not entirely behind us yet. This fact makes it imperative that building owners and managers continue to do what they can to curb viral transmission as the country reopens and tenants return to commercial properties.

One way to do that is by upgrading, repairing and adjusting a building’s heating, ventilation and air-conditioning (HVAC) system. Modifications to HVAC systems can help mitigate viral spread by purifying air, improving ventilation and managing airflows. 

Below is a list of best practices from two of the leading sources of information on this topic throughout the pandemic, the U.S. Centers for Disease Control and Prevention (CDC) and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).

• Bring in more outside air. Amid mild weather, open outdoor air dampers beyond minimum settings to reduce HVAC air recirculation, and open windows and doors to increase outdoor air flow. This may be difficult with summer weather and in areas with heavily polluted air, however.

• Use fans to increase the benefits of open windows. Place a fan safely and securely in a window to pull air from rooms into the outdoors. This practice helps draw outdoor air into rooms through other open windows and doors without creating strong air currents in rooms. In larger facilities, similar results can be achieved using gable fans and roof ventilators.

• Use an air economizer within existing HVAC systems, or add a dedicated outdoor air system (DOAS), also known as a makeup air unit. A DOAS covers the deficit when an existing system can’t match the recommended amount of ventilation, improving indoor air quality and helping to control humidity inside a building.

• Using a humidifier within an HVAC system, or dehumidifying the air with a reheat process or other technique, can help to keep relative indoor humidity levels between 40 percent and 60 percent, as recommended by the American Society for Microbiology. Humidity levels within that range may hinder viruses’ ability to spread and survive in open air, and may increase the human body’s ability to filter out viruses by keeping mucus membranes hydrated and improving immune-system functions.

• Ensure that ventilation systems are operating properly and are providing acceptable indoor air quality for each room’s occupancy level.

• Rebalance or adjust HVAC systems to augment total airflow to occupied spaces whenever possible. Bring cleaner air into high-traffic areas where the air is less clean by evaluating and repositioning supply louvers, exhaust air grilles and damper settings.

  HVAC technicians should re-evaluate the positioning of supply and exhaust air diffusers and dampers and adjust zone supply and exhaust flow rates to establish measurable pressure differentials. This practice is easier to follow when the supply and exhaust points are located in a ceiling grid system.

• When a building is occupied, turn off any demand-controlled ventilation (DCV) controls that reduce air circulation based on occupancy level or temperature. In buildings where HVAC fan operation can be controlled by thermostat, set the fan to the “on” position instead of “auto” to keep it running continuously, even when heating or air-conditioning isn’t required.

• Be sure that restroom exhaust fans are functional and operating at full capacity when the building is occupied.

• Inspect and maintain exhaust ventilation systems in areas such as kitchens, and operate these systems whenever these spaces are occupied. To increase overall ventilation within an occupied building, owners and managers may even consider operating ventilation systems when these specific areas aren’t occupied. 

• Upgrading existing air filters may be an effective and relatively inexpensive solution if efficient filters are already part of the HVAC system. 

An air filter’s effectiveness at capturing and holding airborne particles is expressed by its MERV, or minimum efficiency reporting value. Standard filters have a MERV ranging from 1 to 16, and the higher the number, the better its filtering properties. Filters with a MERV of 13 or greater are efficient at capturing airborne viruses, though a MERV of 14 or higher is preferred.

HEPA (high-efficiency particulate air) and ULPA (ultra-low particulate air) filters are even more effective than the highest-rated MERV filters. HEPA filters are required to remove 99.97 percent of particulates that are three microns or larger in size. It’s important to note, however, that COVID-19 particles can be as small as one micron, or one-thousandth of a millimeter, so even the best filters don’t eliminate the threat of viral transmission. In high-traffic areas, portable HEPA fan and filtration systems are another good way to make air cleaner.

• Make sure air filters are properly sized and within their recommended service life. Inspect filter housing and racks to ensure appropriate filter fit and minimize the amount of air that flows around, instead of through, the filter.

• Consider using ultraviolet germicidal irradiation (UVGI) to kill or deactivate virus particles, especially if options for increasing room ventilation and filtration are limited. 

  UV light has proven effective at killing or deactivating pathogens such as viruses, and lamps that emit UV-C light – which has a shorter wavelength ranging from 100 to 280 nanometers – are the most effective. 

  UV-C installations typically are placed either in filtration systems within HVAC ducting or outside of HVAC ducting. If lights are installed outside of HVAC ducting, they should be positioned near the ceiling to prevent human exposure to UV radiation. In addition, UV-C units should be positioned so that air recirculates across them, since a single pass may not be enough to fully neutralize viral particles. 

• Consider air ionization units, which typically are easy to integrate with existing HVAC systems and are relatively inexpensive to install. Air ionization units use a process known as bipolar ionization to essentially enlarge virus particles, making it easier for filters to capture them. High-voltage electrodes split molecules of oxygen apart into positive and negative ions, and pathogens bind to these ionized molecules, making them easier to trap. 

For more resources and guidance related to the operation of commercial properties during the COVID-19 pandemic and beyond, visit BOMA International’s Coronavirus Resource Center at www.boma.org/coronavirus.