The National Association of Air Duct Specialists UK (NAADUK) has issued a guidance document on the role of ventilation systems in the current pandemic, says Peter Reid.
The NAADUK guidance was created for their members and clients as limited Covid-19 information was available. It is aimed at facilities managers and building owners to help them maintain safe environments for occupants.
The effect of soiled extract/return air grilles in ventilation systems
Soiled extract/return air grilles in ventilation systems will affect the air circulating within the occupied area. Covid-19 stays on hard surfaces for up to three days. There is increased risk of infection because of:
- Reduced air change rate;
- Reduced or no extraction through the grille;
- Increased number of contaminated droplets in contact with people; Increased number of contaminated droplets depositing on surfaces; and
- Longer exposure time of occupants to virus and bacteria.
- A complete clean of extract (and supply) grilles ensures that critical air change rates can be achieved.
How to improve ventilation hygiene during the crisis
As we learn more about this virus, there are basic actions that can be taken to improve indoor air quality and make the occupied areas safer.
- Ventilate space with outdoor air if possible;
- Run the systems at lower speed over a weekend period;
- Keep toilet ventilation in operation 24/7;
- Switch all air handling units with recirculation to 100 per cent outdoor area; and
- Visually inspect all ductwork systems at the grilles and diffusers as blocked grilles and grille dampers reduce ventilation and increase the risk of Covid-19 transmission.
If the building is unoccupied it is an ideal time to carry out essential duct cleaning work. Replace all HVAC filters as the maintenance schedule sets out, while wearing appropriate personal protective equipment (PPE) and respiratory protective equipment (RPE). Most general ventilation systems contain panel and bag filters that will not remove microorganisms and viruses, including Covid-19.
How to use the fan coil unit operation to manage Covid-19 transmission
Fan coil units are a concern for the transmission of Covid-19 owing to the way they function within an occupied space. They are generally installed above the ceilings and recirculate the air locally within the space.
In large open-plan offices, there may be large quantities of fan coil units installed. These units generally contain coarse filters that do not filter small particles and may load with particles containing microorganisms.
Consider the following operation procedures:
- If there is no significant cooling load, turn off the fan coil units altogether to avoid reintroduction of the virus;
- Kill any microorganisms or viruses lodged on the filter by heating up the fan coil unit to 60 °C for one hour or 40 °C throughout the day;
- If the fan coil unit cannot be switched off, run the fan continuously. Viruses can lodge on the filters and a resuspension boost can occur on start-up when the fan is switched on; and
- Maximise exhaust ventilation to remove virus particles.
NAADUK recommends the following:
- Concentrate on cleaning extract air systems, particularly toilet extract systems and recirculating air systems in hospitals, offices and factories.
- Clean supply and extract systems in areas where Covid-19 infections occurred and also decontaminate the buildings if equipped to do so.
- Carry out duct cleaning and damper testing while buildings are unoccupied so that when staff or guests return (offices, shops and hotels) the buildings are safe and ready for use.
- Make sure that anyone engaged on ductwork cleaning is compliant with proper training and certification in order to protect yourselves and the occupants of the building.
Always follow government guidelines on Covid-19 by social distancing and handwashing. And always wear PPE and RPE when working.
The full document on Covid 19 Guidance for Ventilation Systems can be downloaded free of charge from www.naaduk.co.uk.
Peter Reid FIC is president of NAADUK