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.
Trafik-, Bygge- og Boligstyrelsen har på baggrund af REHVAs anbefalinger udarbejdet følgende dokument.
Increase air supply and exhaust ventilation
In buildings with mechanical ventilation systems, extended operation times are recommended for these systems. Adjust the clock times of system timers to start ventilation at the nominal speed at least 2 hours before the building opening time and switch to a lower speed 2 hours after the building usage time. In demand-controlled ventilation systems, change the CO2 setpoint to 400 ppm in order to maintain the operation at nominal speed. Keep the ventilation on 24/7, with lower (but not switched off) ventilation rates when people are absent6. In buildings that have been vacated due to the pandemic (some offices or educational buildings), it is not recommended to switch ventilation needed to normal duct cleaning and maintenance procedures. Much more important is to increase
the outside air supply and to avoid recirculation of air according to the recommendations above.
Change of outdoor air filters is not necessary
In the COVID-19 context, questions have been asked about filter replacement and the protective
effect in very rare cases of outdoor virus contamination, for instance, if air exhausts are close to air
intakes. Modern ventilation systems (air handling units) are equipped with fine outdoor air filters
right after the outdoor air intake (filter class F7 or F88 or ISO ePM2.5 or ePM1), which filter particulate
matter from the outdoor air well. The size of the smallest viral particles in respiratory aerosols is
about 0.2 m (PM0.2), smaller than the capture area of F8 filters (capture efficiency 65-90% for PM1).
Still, the majority of viral material is already within the capture area of filters. This implies that in
rare cases of virus-contaminated outdoor air, standard fine outdoor air filters provide reasonable
protection for a low concentration and occasional occurrence of viral material in outdoor air.
Heat recovery and recirculation sections are equipped with less effective medium or coarse extract
air filters (G4/M5 or ISO coarse/ePM10) whose aim is to protect equipment against dust. These filters
have a very low capture efficiency for viral material (see Section 4.4 for heat recovery and 4.5 for
From the filter replacement perspective, normal maintenance procedures can be used. Clogged
filters are not a source of contamination in this context, but they reduce supply airflow, which has a
negative effect on reducing indoor contamination levels. Thus, filters must be replaced according to
the normal procedures when pressure or time limits are exceeded, or according to scheduled
maintenance. In conclusion, it is not recommended to change existing outdoor air filters and replace
them with other types of filters, nor is it recommended to change them sooner than usual.
Safety procedures for maintenance personnel
HVAC maintenance personnel may be at risk when conducting scheduled maintenance, inspection or
replacement of filters (especially extract air filters) if standard safety procedures are not followed.
To be safe always assume that filters, extract air ducts, and heat recovery equipment may have
active microbiological material on them, including viable viruses. This is particularly important in
any building where there has recently been an infection. Filters should be changed with the system
turned off, while wearing gloves and respiratory protection and disposed of in a sealed bag.
Room air cleaners and UVGI can be useful in specific situations
Room air cleaners remove particles from the air, which provides a similar effect compared to the
outdoor air ventilation. To be effective, air cleaners need to have HEPA filter efficiency, i.e., to have
a HEPA filter as the last step. Unfortunately, most attractively priced room air cleaners are not
effective enough. Devices that use electrostatic filtration principles instead of HEPA filters (not the
same as room ionizers!) often work with similar efficiency. Because the airflow through air cleaners
is limited, the floor area they can serve is usually quite small. To select the right size air cleaner,
the airflow capacity of the unit (at an acceptable noise level) has to be at least 2 ACH and will have
positive effect until 5 ACHxlvi (calculate the airflow rate through the air cleaner in m3/h by multiplying
the room volume by 2 or 5). If air cleaners are used in large spaces, they need to be placed close to
people in a space and should not be placed in the corner and out of sight. Special UVGI disinfection
equipment may be installed in return air ducts in systems with recirculation, or installed in room, to inactivate viruses and bacteria. Such equipment, mostly used in health care facilities needs to be correctly sized, installed and maintained. Therefore, air cleaners are an easy to apply short term
mitigation measure, but in the longer run, ventilation system improvements to achieve adequate
outdoor air ventilation rates are needed.
Toilet lid use instructions
If toilet seats are equipped with lids, it is recommended to flush the toilets with lids closed to
minimize the release of droplets and droplet residues from air flows. Building occupants should
be clearly instructed to use the lids. Water seals must work at all times. Regularly check the water
seals (drains and U-traps) and add water if required, at least every three weeks.
Risk of Legionellosis after shut-down
Throughout the duration of the SARS-CoV-2 (COVID-19) epidemic, many buildings have been
experiencing reduced use or complete shut-down over extended periods of time. This includes, for
example, hotels/resorts, schools, sports facilities, gyms, swimming pools, bath houses and many
other types of buildings and facilities equipped with HVAC and water systems.
Depending on a variety of factors, including system layout and design, prolonged reduced (or no) use
can lead to water stagnation in parts of the HVAC and water systems, enhancing the risks of an
outbreak of Legionnaires’ disease (Legionellosis) upon reassuming full operation.
Before restarting the system, a thorough risk analysis should be carried out to assess any Legionellosis
risks involved. Several relevant authorities provide information on related risk assessment and restart
The risk of indoor cross-contamination via aerosols is very high when rooms are not ventilated well.
If ventilation control needs actions by occupants (hybrid or natural ventilation systems) or there is
no dedicated ventilation system in the building, it is recommended to install CO2 sensors at the
occupied zone that warn against underventilation especially in spaces that are often used for one
hour or more by groups of people, such as classrooms, meeting rooms, restaurants, During an
epidemic it is recommended to temporarily change the default settings of the traffic light indicator
so that the yellow/orange light (or warning) is set to 800 ppm and the red light (or alarm) up to 1000
ppm in order trigger prompt action to achieve sufficient ventilation even in situations with reduced
occupancy. In some cases, standalone CO2 sensors or ‘CO2 traffic lights’ can be used, see an example
in the Specific Guidance document for School Buildings. Sometimes it may work better to use CO2
sensors that are part of a web-based sensor network. The signals from these sensors can be used to
warn building occupants to use operable windows and mechanical ventilation systems with multiple
settings in the right way. One can also store the data and, provide facility managers with weekly or
monthly data so that they know what is going on in their building and rooms with high concentration
and subsequently identify the infection risk.