Last updated 25th March 2020
There is significant interest in the role that heating, ventilation and air-conditioning (HVAC) play in the transmission of coronavirus (COVID-19). We tell you what you need to know, the implications and the steps you need to take.
First reported on 31st December 2019 in Wuhan City, coronavirus is an infectious disease that may cause illness in humans and animals. People who have coronavirus may experience a cough, a sore throat, a fever, fatigue and shortness of breath. Research suggests that the virus is transmitted from person to person, either via close contact with an infected person or through droplets of fluid from the nose or mouth. People can catch COVID-19 if they breathe in droplets from an infected person who coughs, sneezes or exhales droplets. These droplets also land on surfaces and objects nearby. People can also catch COVID-19 when they touch these surfaces, and then touch their mouth, nose or eyes. Alarmingly, it is believed that the virus may survive on surfaces for up to 9 days. Professor of architectural engineering at the Pennsylvania State University, Bahnfleth, states that,
“… there’s also the potential for airborne transmission. And if viruses that are viable are in those droplets that you’re producing, some of them will be small enough that they will stay airborne for a long time. So, it’s not impossible that infectious particles in the air could stay aloft long enough to be collected, say at the return grille of an HVAC system, go through a duct, and infect someone in a different space.”
A.G. Coombs Group is the leading Australian building services company. According to their Advisory Note of 18th March 2020,
“Droplet nuclei (2.5 to 10 µm) are believed to be able to remain suspended in air for hours and therefore be entrained into HVAC systems.”
n the last few days, it has been found in a study recently published in New England Journal of Medicine (DOI: 10.1056/NEJMc2004973) that COVID-19 can be active for several hours airborne:
“Our results indicate that aerosol and fomite transmission of SARS-CoV-2 is plausible, since the virus can remain viable and infectious in aerosols for hours and on surfaces up to days (depending on the inoculum shed).”
A typical HVAC system recirculates filtered air. A portion of outside air is added and a similar portion is exhausted. A droplet infected with a virus like coronavirus would travel through ducting and would settle on surfaces including air filters, fans, grilles and dampers. According to A.G. Coombs Group,
“There is a good likelihood that a particle would impact, entrain and dry on a surface.”
The role of air filters is to trap particles to help prevent them entering the system in the first place. So would it be advisable to upgrade the level of air filtration to a HEPA (high efficiency particulate arrestance) filter? In reality, it’s not that simple.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has published a position document (along with other response resources) which states that HEPA filters are 99.97% effective in trapping particles down to 0.3 microns. It goes on to say that, like many viruses, coronavirus particles measure only between 0.06 and 0.14 microns, and quotes Bahnfleth as saying,
“Even HEPA filters that have been tested in the laboratory with viruses will have some level of penetration. Not much — a few percent.”
So, whilst HEPA filters offer some level of protection, they can’t guarantee absolute protection against virus transmission. In addition, not all fans are capable of creating the speed of airflow necessary to push air through HEPA filters.
The A.G. Coombs Group Advisory Note, written by senior Mechanical Engineer, Matthew Peacock, also recognises that HEPA filters may not be suitable for all HVAC systems, however, it does recommend checking the condition of the air filter and upgrading the filter media to F7 – F9 grade to reduce transmission of COVID-19 through the system. This is just one of the measures recommended by the report, which says that, according to research, droplets are less likely to be transmitted through a properly maintained HVAC system. In brief, other recommended measures include:
- Changing air filters*
- Conducting a cleanliness audit
- Cleaning or disinfecting the HVAC system
- Carrying out preventative maintenance
- Checking air flow rates and controls and, if possible, increasing the outside air rates
- Maintaining internal humidity in the range of 40 – 60% RH
* At HVDS, we recommend changing filters regularly and to a set schedule, rather than relying on final pressure.
View the full report and recommendations here.
HVDS continues to take a holistic approach to Indoor Air Quality (IAQ) Management, in accordance with the current recommendations. Moreover, in the light of coronavirus, it is likely that there will be additional stipulations for food manufacturers. Proactive steps now will help manufacturers meet these in good time and remain audit compliant. For this reason, HVDS is including system surveys for contract customers on top of their existing service at no extra cost.
For more information or to book your complimentary survey, please contact HVDS here.