Ventilation and air conditioning installations are an essential prerequisite for the proper functioning of many buildings. Regular maintenance and servicing are crucial for the safe operation of the systems and the well-being of occupants. Given the current coronavirus pandemic, manufacturers, specialists, and facility managers face questions about the operation of systems and installations in buildings that have not yet been clarified by official authorities. In this document, the FGK association, the RLT manufacturers’ association, and BTGA summarize the current recommendations based on the state of knowledge about the coronavirus SARS-CoV-2 (Covid-19). As soon as additional information becomes available, these recommendations will be updated accordingly.
Mechanical ventilation systems with variable air volume control, when properly designed and operated, significantly reduce pollutants by filtering potentially contaminated outdoor air, supplying fresh filtered air into rooms as needed, exhausting used air, and ensuring good indoor air quality. Professional planning, zoning, maintenance, and maintaining slight positive pressure in rooms ensure that contaminants from one area do not spread throughout the entire building.
According to current knowledge, coronaviruses are transmitted through droplet infection. It is generally recommended to ensure good ventilation of indoor spaces with the highest possible proportion of fresh outdoor air.
Recommendations for Ensuring Proper Operation of HVAC Systems:
- Don’t turn off the air handling units supplying outdoor air; do not reduce the outdoor air flow rate.
- Reduce the amount of recirculated air in the systems, if present, in favor of fresh outdoor air.
- If necessary, extend the operating time of the ventilation devices before and after the regular working hours.
- Local air handling units (fan coil units, induction devices) are effective only in their respective individual rooms and do not transfer air to other rooms.
- Minimize the mixing of air between different zones. It should be noted that air transfer from one room to another is practically difficult to eliminate completely due to doors, windows, and leaks.
Transmission of Coronaviruses via Ventilation and Air Conditioning Systems
According to current knowledge, the transmission of coronaviruses through ventilation and/or air conditioning systems can be ruled out. When filtering fresh outdoor air, droplets that may contain coronaviruses cannot reach indoor spaces through the duct network. The exhaust ducts, where contaminated virus-containing droplets enter, do not transport them to other areas because the system operates under negative pressure, and therefore, the used air should not flow into other rooms.
Depending on the design of the air handling central units (air conditioning and ventilation chambers, and energy recovery ventilation units), internal leaks within the device or in the energy recovery section can lead to mixing of exhaust and supply air. Proper design and high-quality concepts ensure that this will not be allowed:
- Positive pressure in the supply air section and negative pressure in the exhaust air section: With the correct arrangement of components in the air conditioning and ventilation chambers to ensure positive and negative pressure, it is not possible for air to transfer from the exhaust section to the supply air for the rooms—even through heat recovery systems such as rotary regenerative heat exchangers.
- If the supply and exhaust air systems are equipped with a plate-type air-to-air heat exchanger made from a material that prevents mixing of the two air streams, then the transfer of viruses can be eliminated.
- If the supply and exhaust air systems are installed separately, for example using a heat recovery system with an intermediate heat carrier, the transfer of viruses and bacteria can be completely eliminated. Such systems are recommended for operating rooms, hospitals, and similar environments.
Filtration
Air filters provide a reduction in the concentration of dust and aerosols in air conditioning and ventilation systems in the air supplied to rooms. HEPA filters are used for complete separation of suspended particles, including the smallest viruses (22–330 nm [nanometers]). In this way, filtered air is required in air handling systems for clean rooms, operating theaters in hospitals, or special laboratories. Using filters of class H13 / H14 helps to almost completely settle substances containing viruses. Significant reduction is also achieved when using a filter with class ePM1 > 80% (formerly F9).
Maintenance of Filter Systems
Viruses are always associated with aerosols or dust particles and therefore they usually do not float freely in the air. Consequently, they accumulate in the filter material, just like all other particles. Personal protective equipment (protective clothing, protective mask, and safety goggles) must always be worn when maintaining and replacing contaminated filters.
Humidity in Indoor Spaces
The humidity of the air in a room can also play a role in the transmission of viruses. Studies have already shown that the transmission of influenza viruses decreases when indoor air humidity is maintained between 40% and 60%. It is not yet known whether this also applies to coronavirus infections. If humidity control is possible through the ventilation and air conditioning system, it should be managed as follows:
- The indoor air humidity should be maintained between 30% and 65% RH (relative humidity).
- For systems without humidification, it is important to consider what level of ventilation is appropriate given the current occupancy rate.
Additional sources:
- [1] Robert Koch Institute (RKI) / CCI: Should ventilation systems be turned off as a precautionary measure against the transmission of COVID-19 („coronaviruses“)?
RKI responded: Since COVID-19 is an infection mainly transmitted through droplets (and is not transmitted through duct networks), it is not assumed—based on current knowledge—that SARS-CoV-2 will be spread through a functioning ventilation system (for example, in public buildings, hotels). This leads to the conclusion that such systems should remain operational in order to supply fresh outdoor air.
- [2] COVID-19 Infection Prevention and Control Guidance in Healthcare Settings by the Department of Health and Social Care (DHSC), Public Health Wales (PHW), Public Health Agency (PHA), Northern Ireland, Health Protection Scotland (HPS), and Public Health England as the official guidance:
- [3] INTERNATIONAL GUIDANCE DOCUMENT Clinical management of severe acute respiratory infections when a novel coronavirus is suspected: What to do and what not to do: Airborne precautions. Ensure that healthcare workers performing aerosol-generating procedures use PPE, including gloves, protective gowns, respiratory protection with masks, and eye protection (N95 or equivalent). Whenever possible, use adequately ventilated single rooms when performing aerosol-generating procedures.
[4] Comment by Prof. Dr. Med. Eng. Hans-Martin Seipp, Technische Hochschule Mittelhessen – 07.03.2020 Excerpt: HVAC systems can only operate if:
- Recirculated airflows [are safe] only with HEPA filters (HEPA filters are completely safe starting from class H-13!). From F-9 – depending on the load condition – the risk begins to decrease.
- They supply exclusively fresh filtered outdoor air.
- [5] Environmental contamination and personal protective equipment from severe acute respiratory syndrome coronavirus (SARS-CoV-2) by a symptomatic patient.
JAMA Published online March 4, 2020
[6] Walter Hugentobler, MD, Comment on COVID-19 guidance, 23.03.2020
Translation by the team of the company ‘TANGRA – AV’ Ltd
