In addition to social distancing and the wearing of masks in preparation for the easing of restrictions, there are several changes to BeMS and HVAC that can help. Based on REHVA recommendations, here are our 10 things to make your building safer from COVID-19.
The recommendations given in this blog are taken from the “REHVA COVID-19 guidance document, April 3, 2020”. Although this blog was correct at the time of posting, the source document may be subject to revision if new scientific evidence is reported and readers are urged to visit the REHVA website for the latest advice.
Where a ventilation system is fitted, extended operation times are recommended. Adjust timers to begin ventilation, at normal speed at least 2 hours before, and 2 hours after normal occupancy times.
In short, supply as much outside air as is reasonably possible.
Exhaust ventilation in washrooms should be kept on 24/7, making sure that a slight negative pressure is maintained to avoid fᴂcal-oral transmission
The general recommendation is to stay away from crowded and poorly ventilated spaces. In buildings without mechanical ventilation systems, it is recommended to actively use operable windows more frequently than is usual, and even at the expense of a comfortable temperature. It is advisable to open windows for ~15 minutes when entering, especially when the room has been previously occupied beforehand.
Even when ventilation systems are being used, ventilation can be further increased by window airing.
However, avoid opening windows in toilets to ensure that ventilation is going in the right direction to prevent fᴂcal-oral transmission.
Coronaviruses are resistant to environmental changes and only extremes, such as RH >80% and temperatures ≥30ºC, have any effect.
There is a risk that heat recovery devices could carry over the virus attached to particles from the exhaust side to the supply side, via air-leaks.
Regenerative thermal wheels may be susceptible to significant leakage due to poor design or lack of maintenance. The most common fault is that fans are mounted such that a higher pressure is created on the exhaust side, causing leakage into the supply air.
If a leak in the heat recovery system is suspected, pressure adjustment or bypassing is recommended.
Virus particles can re-enter a building when air-handling units are equipped with recirculators. These should be avoided by closing the recirculation dampers, either via BeMS or manually. Whilst this may cause problems with heating or cooling capacity, this must be accepted.
Dampers should be closed even if filters are fitted as standard efficiency filters (F4/F5 or ISO coarse / ePM10 class) will not filter out virus particles.
Some fan coil and induction systems operate with room-level circulation. If possible, it is recommended that these units are turned off as the fan coil units have a coarse filter that will not stop the virus. If they cannot be switched off, it is recommended that they run continuously to prevent the virus from forming a sediment in filters which becomes re-suspended when the fan is turned on.
Viruses attached to small particles will not deposit easily in ventilation ducts and will normally be carried out by the airflow.
Instances of outdoor virus contamination are rare, and even if air exhausts are close to air intakes, at 80-160 nm, the virus is much smaller than the capture area of normal outdoor air filters (F7 or F84 or ISO ePM2.5 or ePM1).
To be effective air cleansers need at least HEPA level efficiency. However, because airflow through air cleansers is limited, the area of floor covered effectively is typically <10 m2.
Devices that use electrostatic filtration systems (not the same as portable room ionisers) can be effective, as can specialist UV cleaning equipment.
Starting and stopping fans can dislodge particles which has settled in the ducting.