Can HVAC play a role in the transmission of COVID-19? The risk of a well-maintained HVAC system in a modern commercial building causing transmission of the COVID-19 is understood to be low. Read the article below to learn how HVAC systems can be used to assist in reducing the spread of infections.
Coronaviruses are a family of viruses that can cause illness to humans and animals. A new coronavirus known as COVID-19 was first reported on 31 December 2019 in Wuhan City in China.
Symptoms of the virus can range from mild illness to pneumonia. People with COVID-19 may experience fever, flu-like symptoms such as coughing, sore throat, fatigue and shortness of breath.
At the time of writing, the transmission mechanisms were not fully understood. It is believed that the virus can be transmitted from person-to-person, most likely through close contact with an infectious person, or contact with droplets of fluid from an infected person’s cough or sneeze. It is also believed that transmission can occur by touching surfaces that have droplets from an infected person, and then touching the mouth or face. It is believed that the virus may survive for up to 9 days on some surfaces in the right conditions.
When a person infected with an illness coughs or sneezes, pathogens can be encapsulated within droplets of fluid and discharged into the air. Different illnesses are known to result in differing droplet sizes. It is not yet certain what size droplets are produced by people infected with COVID-19.
It is known that large droplets (>60 µm) normally are too large to remain suspended in the air and usually fall and land on surfaces. In some instances, some of the fluid can evaporate and the large droplets can transform into smaller particles called droplet nuclei and these can remain suspended in the air. Droplet nuclei (2.5 to 10 µm) are believed to be able to remain suspended in the air for hours and therefore be entrained into HVAC systems.
HVAC Systems Explained
Heating Ventilating and Air Conditioning (HVAC) systems exist in many formats. The diagram depicts a typical HVAC system commonly found in commercial and institutional buildings. It is fundamentally a recirculating system with a portion of outside air added continually whilst a similar portion is exhausted. The outside air rate can be varied in many systems. Air is filtered before recirculation and moved around the system using fans. Heating and cooling are typically provided by finned coils using heating or chilled water.
The journey that a virally infected droplet would experience to arrive back in an occupied space would typically include extended ducted air pathways, multiple changes in direction and air velocity, and multiple impacting surfaces including air filters, fans, dampers, and grilles. There is a good likelihood that a particle would impact, entrain and dry on a surface.
While published research on healthcare ventilation systems and scenarios suggests that the transmission of droplets containing viral material is theoretically possible in these situations, it is thought to be less likely in a well-designed and properly maintained typical HVAC system in a public setting.
There are a number of practical HVAC operational measures that can be addressed along with possible system changes to reduce the likelihood of a virus spreading including the following:
- Maintenance regimes and essential safety measures
- Cleaning and disinfection
- System commissioning and operation, and outside air rates
- Air filtration and cleaning options