The special feature of the UV-Sky ceiling unit is the room air flow: the exhaled air is captured both by the thermal effect and by the suction of the ceiling unit at the ceiling without being distributed further in the room. It is sterilized in the unit and blown out parallel to the ceiling. Due to the Coanda effect, the air flows along the ceiling to the walls. Since the walls are usually colder than the room air, the air is cooled there, sinks towards the floor and is distributed there. Thus, the displacement air system is realized. The exhaled air, contaminated with aerosols, possibly viruses, does not mix with the room air first, but is led directly towards the unit and cleaned. In this way, the people in the room are supplied with clean source air from below. The concern of sucking in impurities from the floor that have settled on the floor is not relevant, as there are only particles on the floor that have a higher sinking speed than the room air flow.