COVID-19 Info

CONTROLLING COVID-19 TRANSFERENCE Through Heating, Ventilation & Air-Conditioning Systems


While information regarding the exact mode of transmission of COVID-19 is limited, some cases demonstrate that the virus can be transferred as the result of virus-laden aerosolized droplets traveling through heating, ventilation and air-conditioning (HVAC) systems.

This is further substantiated by World Health Organization (WHO, 2020): Poorly ventilated buildings affect air quality and can contribute to the spread of disease. Microorganisms, such as those causing tuberculosis and legionellosis, can be transmitted by air-conditioning systems, particularly when they are poorly maintained or when the number of air exchanges per hour in a room is insufficient. Table 1 illustrates the risk reduction as it relates to an increase of ACH for healthcare workers
While the acceptable level of risk is defined by each respective organization, one would struggle to make an affirmative argument that ACH values of less than 6 are acceptable in environments supported by mechanical ventilation where there is known to be, or could potentially be, an active source of COVID-19 infection

Conclusion Given the information discussed and data available, the best course of action to prevent the spread of COVID-19 via an HVAC unit is to 1) ensure that potentially infectious individuals are not within 5 meters (about 16.5 ft) of the HVAC inlet duct;
2) measure the ACH of each affected space and take necessary steps to achieve an ACH value of 6 or greater; and
3) install air sanitation filters, UV light systems (or both) on the inlet side of HVAC systems that recirculate air from inside the building. These tertiary controls should prove effective in preventing the transference of COVID-19 through HVAC systems.

Air Filtration Fluid droplets from the cough or sneeze of an infected person are typically 5 microns (5 x 10-6 m) or larger. HEPA filters reliably capture 99.97% of particles that are 0.3 microns in diameter with efficiency increasing for both smaller and larger particles. The smallest particle one might be concerned with is a single virion (unattached to any fluid droplet), having a diameter of approximately 0.12 microns. While these are conceivably filterable by a HEPA filter, ULPA filters are even better, catching 99.99% of particles 0.12 microns and larger. In theory, all COVID-19 virions could be filtered and captured, assuming that they can be brought into contact with an air filter (Elias & Bar-Yam, 2020). Both HEPA and ULPA type filters are available for most industrial and residential HVAC systems and are more than adequate to capture and contain COVID-19 virus-laden particles. When selecting, one should note the minimum efficiency reporting value (MERV) assigned to the respective filter (EPA, 2020). The MERV rating indicates, on a scale of 1 to 16, how effectively a filter traps small particles

UV Germicidal Irradiation Systems Unlike a standard air filter or an electrostatic air cleaner, a UV air treatment system uses concentrated UV light to destroy a wide array of indoor air pollutants. These systems may also be equipped with an enhanced filter (e.g., HEPA) to provide additional protection against airborne dust, microorganisms and other particulates. UV light can harm several types of microorganisms including mold, mildew, fungi, bacteria and viruses by breaking down molecular bonds in their DNA. Exposure to UV light either kills the bio-contaminants or renders them unable to reproduce. The UV air treatment system works in tandem with the HVAC system and is mounted inside of the system’s ductwork. When the air circulates through the ducts, pollutants are destroyed as the air passes through the UV rays (HVAC & Plumbing Unlimited, 2020).