Jon A. Barrett

Indoor air quality is extremely important for productivity and occupant health in any industrial, commercial, or residential property. HVAC air conveyance systems, with associated ductwork and ductless mini-split systems, provide acceptable indoor air quality atmospheres. However, they must be routinely inspected, maintained, and cleaned to operate most efficiently and cost effectively. This routine includes cleaning the interior of the ductwork and replacing filters. Air conveyance systems filter out dust, particulates, volatile organic compounds (VOCs), mold spores, bacteria, and viruses. These systems also lower humidity levels while removing moisture levels in a building. Unfortunately, dust, particulates, VOCs, mold spores, bacteria, and viruses can accumulate on the interior surfaces of air conveyance systems and interior ductwork. This accumulated debris can be aerosolized and transmitted through air currents. [caption id="attachment_11546" align="aligncenter" width="377"] Duct with particulate buildup.[/caption] Studies on virus transmission In regard to SARS-CoV-2 transmission, a 2020 Florida Atlantic University study showed that a human sneeze or cough can disperse smaller droplet nuclei into air currents up to 12 feet away and linger in the air for more than one minute. A study conducted in an MIT laboratory using high-speed cameras and light confirmed that a fine mist of saliva and mucous can burst from a person’s mouth at nearly 100 miles per hour and can travel as far as 27 feet. Research suggests it is possible coronavirus droplets can be aerosolized, carried, and transmitted through HVAC duct systems. A ducted HVAC system creates air currents, which can likely carry smaller viral particles even further. A research letter published in the U.S. Centers for Disease Control and Prevention’s (CDC) Emerging Infectious Diseases journal in July 2020 detailed a COVID-19 outbreak associated with air conditioning in a restaurant in Guangzhou, China. Ten people from three families eating in the restaurant became infected. Aerosolized droplet transmission was prompted by air-conditioned ventilation. A video from the restaurant showed many of these patrons were sitting more than six feet apart from one another. Researchers concluded strong airflow from the air conditioner could have propagated droplets from one table to another and back. Research published on nature.com in July 2020 detailed an ongoing study of environmental contamination that obtained surface and air samples in two Nebraska Biocontainment Units (NBUs) and nine residential isolation rooms housing individuals who tested positive for SARS-CoV-2. Room surfaces tested included ventilation grates, tabletops, and window ledges. Virus samples with the highest concentration were recovered from an air-handling grate in the NBU. Airflow in the NBU suites originated from a register at the top center of the room and exited from grates near the head of the patient’s bed on either side of the room. Airflow modeling suggested that some fraction of the airflow was directed under the patient’s bed, which may have caused the observed contamination under the bed, while the dominant airflow likely carried particles away from the patient’s bed toward the edges of the room, passing by the windows, resulting in some deposition there. The New England Journal of Medicine published a letter to the editor in March 2020 from a group of researchers who studied the stability of SARS-CoV-2 in aerosols and on various surfaces. Their research indicated that infectious aerosol may persist for several hours and on surfaces for as long as two days. The most prolonged viability of viruses was on stainless steel and plastic. The estimated median half-life of SARS-CoV-2 was approximately 5.6 hours on stainless steel and 6.8 hours on plastic. In conjunction, influenza viruses can spread through the air on dust, fibers, and other microscopic particles, according to research published in August 2020 from the University of California, Davis and the Icahn School of Medicine at Mt. Sinai. [caption id="attachment_11547" align="aligncenter" width="364"] Particulate buildup on a register[/caption] A look at airflow Although ductwork interiors can be made of smooth metal, fine dust can collect on air duct surfaces, vents, motors, and coils. Flakes of dead skin, hair, and pet dander catch onto the dust, and before long, this process creates a dense, mat-like environment where viruses, bacteria, mold, dust mites, and allergens can flourish. This is similar to a vehicle’s exterior during a spring pollen season, as the pollen would coat the vehicle and windows. For instance, when dust is carried on air currents generated by air conditioning and similar devices, the dust takes on a positive or negative static electric charge as it makes contact with various objects. Dust with a positive electric charge will be attracted to objects with a negative electric charge and vice versa. The greater the amount of dust in the air, the more considerable the amount of dust that clings to objects within the room. Also, if sources of dust (mainly people and clothing) are electrically charged, the dust that is generated from these sources is electrically charged as well. This attractive force generated by static electricity is known as the “Coulomb force.” Also, ductwork return airstreams contain levels of humidity and moisture. As a result, this moisture can adhere to the ductwork interior and capture dust particulate. HVAC air filters might help in capturing the viral particles and dust particulates. A high-efficiency particulate air (HEPA) filter effectively removes small particles, 99.7% of particles sized 0.3 microns. A minimum efficiency reporting value (MERV) filter removes larger particles, 0.3 microns to 10 microns. A MERV filter rated 17 or higher is considered HEPA-like in efficiency. However, most commercial buildings have MERV filters rated 12 or lower. Unfortunately, a coronavirus particle is about 0.1 microns and cannot be viewed with human eyesight. So, there’s no guarantee that a HEPA filter would stop viral particles and dust particulates. Current standard air handling units (AHUs) in HVAC systems circulate up to 80 to 90% of the air in regular systems during peak-load conditions such as in winter and summer when outdoor ventilation airflow is set at the minimum percentage to save energy. Standard filtration units in HVAC systems cannot remove the virus within an airstream effectively. The HVAC system has become a central

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Jon A. Barrett

Marketing manager of SERVPRO of Blackwood and Gloucester Township, New Jersey

Articles by Jon A. Barrett

COVID-19 and HVAC Systems

Health and Safety

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