Answer
As things stand, ventilation and air-conditioning systems do not pose an increased risk of infection with the coronavirus as long as they are operated and maintained correctly. To provide good protection, operate the systems with a high fresh air exchange rate and the smallest possible recirculated air component.
Air-conditioning systems that generate constant flows of air between people in a poorly ventilated room can pose a risk. Rooms without ventilation systems should be aired thoroughly on a regular basis. The smaller the room and the more occupants it has, the more it needs airing. Please follow our recommendations in this regard that you can find on the page Protect yourself and others.