Coronavirus: Anbefalinger fra REHVA omkring forholdsregler for ventilationsanlæg


VELTEK har fra medlemmer modtaget spørgsmål omkring, hvorvidt coronavirus kan spredes via ventilationsanlæg samt hvilke forholdsregler, man eventuelt bør iagttage, eller hvilke råd man kan videregive til kunder og samarbejdspartnere. VELTEK videregiver derfor en række råd og anbefalinger fra REHVA.

Nedenfor gives et par af anbefalingerne fra REHVAs samlede vejledning.

Bemærk; REHVA understreger, at dokumentet vil blive opdateret løbende efterhånden, som der kommer ny viden. Enhver brug af informationen fra REHVA er på eget ansvar.

Hele dokumentet kan downloades her

Trafik-, Bygge- og Boligstyrelsen har på baggrund af REHVAs anbefalinger udarbejdet følgende dokument.

Download TBSTs dokument her

Increase air supply and exhaust ventilation

In buildings with mechanical ventilation systems extended operation times are recommended. Change the clock times of system timers to start ventilation a couple of hours earlier and switch off later than usual.

Better solution is even to keep the ventilation on 24/7, possibly with lowered (but not switched off) ventilation rates when people are absent. Considering a springtime with small heating and cooling needs, the recommendations above have limited energy penalties, while they help to remove virus particles out of the building and to remove released virus particles from surfaces.

The general advice is to supply as much outside air as reasonably possible. The key aspect is the amount of fresh air supplied per person. If, due to smart working utilization, the number of employees is reduced, do not concentrate the remaining employees in smaller areas but maintain or enlarge the spacing among them in order to foster the ventilation cleaning effect.

Exhaust ventilation systems of toilets should always be kept on 24/7, and make sure that underpressure is created, especially to avoid the faecal-oral transmission.

Use more window airing

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 (much more than normally, even when this causes some thermal discomfort). Window airing then is the only way to boost air exchange rates. One could open windows for 15 min or so when entering the room (especially when the room was occupied by others beforehand).

Also, in buildings with mechanical ventilation, window airing can be used to further boost ventilation. Open windows in toilets with passive stack or mechanical exhaust systems may cause a contaminated airflow from the toilet to other rooms, implying that ventilation begins to work in reverse direction.

Open toilet windows then should be avoided. If there is no adequate exhaust ventilation from toilets and window airing in toilets cannot be avoided, it is important to keep windows open also in other spaces in order to achieve cross flows throughout the building.

Safe use of heat recovery sections

Under certain conditions virus particles in extract air can re-enter the building. Heat recovery devices may carry over virus attached to particles from the exhaust air side to the supply air side via leaks. In rotary heat exchangers (including enthalpy wheels) particles deposit on the return air side of the heat exchanger surface after which they might be resuspended when heat exchanger turns to the supply air side.

Therefore, it is recommended to (temporarily) turn off rotary heat exchangers during SARS-CoV-2 episodes.  If leaks are suspected in the heat recovery sections, pressure adjustment or bypassing can be an option in order to avoid a situation where higher pressure on extract side will cause air leakages to supply side.

Virus particle transmission via heat recovery devices is not an issue when a HVAC system is equipped with a twin coil unit or another heat recovery device that guarantees 100% air separation between return and supply side.

No use of recirculation

Virus particles in return ducts can also re-enter a building when centralized air handling units are equipped with recirculation sectors. It is recommended to avoid central recirculation during SARSCoV-2 episodes: close the recirculation dampers (via the Building Management System or manually).

In case this leads to problems with cooling or heating capacity, this has to be accepted because it is more important to prevent contamination and protect public health than to guarantee thermal comfort.

Sometimes air handling units and recirculation sections are equipped with return air filters. This should not be a reason to keep recirculation dampers open as these filters normally do not filter out particles with viruses effectively since they have standard efficiencies and not HEPA efficiencies.

When possible, decentralized systems such as fan coil units that use local recirculation, also should be turned off to avoid resuspension of virus particles at room level (esp. when rooms are used normally by more than one occupant). Fan coil units have coarse filters which practically do not filter out particles with viruses.

If not possible to turn off, these units are to be included into cleaning campaigns, because they might collect particles as any other surface in the room.

Room air cleaners can be useful in specific situations

Room air cleaners remove effectively particles from air which provides a similar effect compared to ventilation. To be effective, air cleaners need to have at least HEPA filter efficiency. Unfortunately, most of attractively priced room air cleaners are not effective enough.

Devices that use electrostatic filtration principles (not the same as room ionizers!) often work quite well too. Because the airflow through air cleaners is limited, the floor area they can effectively serve is normally quite small, typically less than 10 m2.

If one decides to use an air cleaner (again: increasing regular ventilation often is much more efficient) it is recommended to locate the device close to the breathing zone. Special UV cleaning equipment to be installed for the supply air or room air treatment is also effective as killing bacteria and viruses but this is normally only a suitable solution for the equipment for health care facilities.