Since the first version of the REHVA Guidance document which was published on 17 March, REHVA has received several questions and requests for clarifications from industry, academia and government experts. The authors of the document in an effort to respond to these requests have added this FAQ section that it will be continuously updated as more frequently asked questions arise.
What precautions should I take when changing filters?
Question
Should there be any precautions to be taken when changing filters or cleaning supply vents on a maintenance routine? Are the maintenance personnel at risk while carrying out such works?
Answer
In general, it is wise to assume that filters have active microbiological material on them. Whether this represents an important infectious disease risk from viruses is not known, but the precautionary principle would suggest that care should be taken. This becomes particularly important in any building (including residential) where there are known or similar cases of any infectious disease including COVID-19. The system should be turned off when changing filters and taking all necessary protective measures such as wearing gloves, including an FFP3 respirator if available, outdoors if possible and disposed of in a sealed bag. (Reference)
Is disinfection treatment of air ducts necessary after the pandemic?
Question
Do you recommend to clean air ducts (especially exhaust) with disinfection treatments after the pandemic?
Answer
According to our recommendation this is not necessary, because viruses stay viable no longer than 2-3 days on plastic and stainless steel surfaces. In the ductwork, this time is probably even shorter, as in the airflow they stay viable only for 3 hours.
Can high temperature in fan coil units eliminate viruses?
Question
In the guidance document it is mentioned that the virus is susceptible to temperatures above 30 ºC. In fan coil units, temperatures of 40ºC can be easily reached. Can this be a way to eliminate or reduce viruses in suspension in a building? Would it be advisable to maximise the temperatures of the fan-coil circuit?
Answer
To inactivate the virus, a temperature increase is needed up to 37 ℃ for one day and 56 ℃ for 30 minutes. Considering a safety margin of 3-4 ℃, it would be advisable to operate at 40 ℃ for one day and 60 ℃ for one hour. These temperatures apply mainly for the heat exchanger surfaces and not the filters where temperature is expected to remain at lower levels. Therefore, a filter replacement might be considered if such heating measure will be taken. (Reference)
Are UV lights and ionisation units recommended?
Question
Would you recommend the installation of UV air treatment systems or ionisation units in an existing air handling unit (AHU), given that they won’t increase pressure losses?
Answer
Such installations (UV systems, ionisation units etc.) are more relevant for healthcare facilities. REHVA guidance targets common non-residential buildings and in this case, outdoor air is NOT a contamination source. Therefore, UV-treatment of outdoor air in air handling units is not necessary. This is the reason we do not recommend UV-applications.
Should I suspend fire dampers servicing within ventilation ducts?
Question
A number of engineers have raised concerns regarding the servicing of fire dampers within ventilation ducts. Do you believe we need to suspend this type of servicing during COVID 19 outbreak?
Answer
HVAC maintenance personnel could be at risk when filters (especially extract air filters) are not changed in line with standard safety procedures. To be on the safe side, always assume that filters have active microbiological material on them, including viable viruses. This is particularly important in any building where there recently has been an infection. Filters should be changed with the system turned off, while wearing gloves, with respiratory protection, and disposed of in a sealed bag. It is possible that some virus particles are in extract ducts. Therefore, similar protection could be recommended.
Can virus particles re-enter to the ventilation system via a heat wheel?
Question
Can virus particles enter to the ventilation system via a heat wheel and in particular through the fins, in the same way as moisture particles enter to the system?
Answer
In the case of heat wheels, the carry over transfer is limited mainly to gaseous pollutants, for instance to tobacco smoke and other smells. In the case of properly operating equipment, heat wheels with purge sector practically do not transfer particles – this applies also for virus particles. The main concern in older equipment is the air leakage from exhaust side to supply side. This depends on pressure difference and condition of seals. If fans create higher pressure on the exhaust air side, the air leakage can increase from a few percent to 15%. If needed, the pressure differences can be corrected by dampers or by other arrangements. Because the leakage does not depend on the rotation speed, it is not needed to switch rotors off, but inspection for older equipment can be recommended.
