Respiratory viruses & indoor HVAC systems

The World Health Organisation (WHO) have recently acknowledged growing concerns surrounding the possible airborne transmission of the coronavirus COVID-19. Australian medical officials are closely monitoring the outcome of pending investigations, however, there are no changes to current Australian Government recommendation at this time.

Infectious respiratory viruses are typically spread from person to person through close physical contact with one another or through respiratory droplets which are produced when an infected person coughs or sneezes. These droplets may then be inhaled or come into close contact with the eyes, nose or mouth of another person.

Respiratory droplets are very small, often invisible to the eye, with a particle size ranging from less than 0.5 micron to 15 micron. Standard measures to help mitigate these droplets within indoor HVAC systems include:

Providing sufficient and effective ventilation

• Supply clean outdoor air
• Increase outdoor air ventilation rates
• Minimise recirculating air

Supplementing general ventilation with airborne infection controls

• Local exhaust ventilation
• Opening outdoor air dampers
• High efficiency air filtration, subject to fan capacity limitations
• Portable room air cleaners/purifiers
• Germicidal ultraviolet lights

Ongoing HVAC system maintenance

• Regular changing of air filters
• Cleaning /disinfection of cooling and heating coil surfaces, using approved methods and chemicals

Upgrading to higher efficiency air filters, rated F9 or ePM1 85%, is recommended for HVAC systems with AHUs. However, due to increased resistance to airflow and space restrictions, this may not be practical for every commercial HVAC system.

It should be noted that upgrading particulate air filters may also result in:

• Shorter air filter life
• Higher energy costs of air filtration
• A higher pressure drop that existing fans may not be able to handle (reduced airflow countering the higher efficiency by reducing air change rates)

The next best option is to select the highest-rated air filter your HVAC system can handle, and/or run the system on an economy cycle, with 100% outside air, where possible.

Portable in room air cleaners or air purifiers may also assist with reducing viral load, especially where supplementary localised control is needed.

An interesting US based article, published to the McKinsey and Company website, discusses how modifications to heating, ventilation, and air conditioning systems might help reduce the spread of the coronavirus COVID-19 by purifying air, improving ventilation and managing airflows. The article, written collaboratively by the Advanced Industries Practice was published to the site on July 9, 2020 and is available at the link below.

Can HVAC systems help prevent transmission of COVID-19?

Camfil have a comprehensive range of high-efficiency air filters in stock, ready to fulfill your HVAC filtration needs. We also offer air cleaners and air purifiers for a variety of applications. Please contact us for assistance with selecting the most suitable air filters for your existing HVAC system and for expert advise based on your specific requirements.