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HVAC COVID-19 Air Transmission


Although the World Health Organisation (WHO) initially held that the coronavirus could not be spread through aerosols, it recently reversed its stance. The WHO guidelines now state that airborne transmission of the coronavirus may be possible indoors, especially for people who spend extended periods in crowded, poorly ventilated rooms.

This may also be a good time to think about improving air quality in buildings by significantly changing heating, ventilation, and air-conditioning (HVAC) systems
or by making physical changes to manage indoor airflows.

The WHO’s turnaround came after the organisation received an open letter from 293 scientists asking the organisation to reconsider its position on airborne transmission. Given the concern about airborne transmission, building managers, safety experts, and others might take steps to optimise ventilation and airflow indoors and limit viral spread.

Businesses have already taken steps to make their facilities safer by installing physical barriers, making one-way systems, increasing the frequency of cleaning, widening the space between desks and staggering shifts. This may also be a good time to think about improving air quality in buildings by significantly changing heating, ventilation, and air-conditioning (HVAC) systems
or by making physical changes to manage indoor airflows.

Low-tech strategies for preventing airborne viral transmission

Some low tech / cost strategies that are worth considering for preventing airborne viral transmission are as follows:

  • Rearranging furniture to avoid having several people on the same airflow “corridor”
  • Opening windows in buildings with basic HVAC systems, which cannot filter or pull in outside air, to increase the exchange of fresh air
  • Locking windows in buildings with central HVAC systems, when permissible, to reduce indoor temperature changes; if a fan does not have to increase its speed because of an inflow of warm or cold air, turbulence will remain low
  • Replacing hand dryers with paper towels to reduce air turbulence

HVAC systems can potentially spread a virus across rooms when high-speed air flows past an infected person to others, something that has been shown with Severe Acute Respiratory Syndrome in 2004.

Changes and upgrades to HVAC systems

If airborne transmission is also possible with the coronavirus, a few control-setting changes and upgrades may help decrease the risk of spread through this route.

One step to take involves configuring ducted HVAC systems to increase the rate of exchange with fresh fresh air from outside the building to reduce recirculation. Adjusting the settings may also help. Instead of shutting down overnight or on weekends, for instance, the HVAC system could run without interruption to increase the replacement of air and minimise airflow speeds.

In buildings with old or inflexible systems, it might be worth considering upgrading HVAC hardware. Some of the most important might include these:

  • Replacing fixed-speed fan motors with variable- speed ones to enhance the control of airflow and allow for a minimum setting that produces lower speed airflow
  • Introducing sophisticated airflow-control systems, such as those that are sensitive to pressure, to allow for smoother adjustment of airflows
  • Installing high-performance air-purification systems. These options will be discussed in more detail in our next blog “Methods of Purifying Contaminated Air”

Airflow Management

While studies are still ongoing about how the coronavirus spreads via air, evidence suggests that measures to change indoor airflow patterns could play a role in reducing transmission.

Three main principles apply:

  • Encouraging a vertical laminar rather than turbulent airflow
  • Ensuring a slow, steady air speed
  • Directing potentially contaminated air out of rooms and away from people

The World Health Organisation recently acknowledged that some evidence about in-room transmission is worrisome. In addition, after analysing a transmission event at a restaurant in China, the US Centers for Disease Control and Prevention (CDC) concluded that an asymptomatic patient transmitted the virus to families at two nearby tables. Based on the restaurant layout, seating arrangements, and smear samples from air-conditioning inlets and outlets, the CDC found that the coronavirus was likely transmitted when strong airflows from a nearby air conditioner spread large droplets from the infected person. These droplets traveled more than one meter— further than usual, but less than the distance aerosols can typically travel.

Changing airflow patterns to create laminar vertical airflow—air moving in the same speed and in a straight path—may effectively prevent the airborne transmission of coronavirus particles. This principle is already used to prevent the spread of particles in several settings. For instance, clean rooms and hospital operating rooms minimise contamination via sophisticated systems to direct air from the ceiling to the floor with laminar flow.

Creating airflows that are close to laminar will involve far more than changing HVAC settings.
In new construction, for instance, builders must include a sufficient number of air outlets. In existing structures, it may be necessary to upgrade the outlets in HVAC systems—for instance, by adding some outlets in the space provided by suspended ceilings and replacing outlet covers, which are normally designed to mix and distribute air, with covers that produce laminar flows. For both new and existing buildings, the placement of air outlets is critical and must be based on planned occupancy, room architecture, furniture placement, and other factors that influence airflows.

Inter-room contamination may be something worth considering especially if the coronavirus is found to readily spread via airborne transmission. Firstly you should identify how air moves through rooms before installing new devices or upgrading HVAC systems. Several options are then available, some involving HVAC upgrades and others focusing on simpler changes. These solutions might include installing doors or air curtains, generating overpressure above suspended ceilings, and sealing any gaps in them. 

If you are concerned about COVID-19 airborne transmission we have validated and developed a sampling and analysis methodology that can detect the presence of the SARs-Cov2 virus within the air. For further information please don’t hesitate to contact us


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