The invention relates to a two-channel air-conditioner (10) for the climate control of a number of rooms (44, 46, 48) and/or room zones, having an air inlet device (52) in every room (44, 46, 48) to be climate controlled, having at least one pair of supply air channels (20, 22) wherein at least one supply channel (20, 22) comprises a cooling and/or heating register (32, 34; 58, 60) having at least one temperature regulator for each room (44, 46, 48) to be climate controlled, which keeps the room (44, 46, 48) to be climate controlled at a room temperature (T.sub.room target) which can be set, having valve units (54, 72), which connect the supply air channels (20, 22) to the air inlet device (52). The invention is characterized in that it allows switching, the cooling or heating register (32, 34; 58, 60) is only opened as needed if the temperature in at least on of the supply air channels (20,22) is insufficient for cooling or heating the room (44, 46, 48) to be climate controlled.

The disclosure relates to a method for operating a ventilation system with a mixing chamber into which air is supplied via a first supply duct and via at least one further supply duct. Air is removed from the mixing chamber by a removal duct. The supply of air—volume control—into the mixing chamber from the supply ducts is controlled in each case via flaps with a plurality of flap leaves and/or a plurality of flap units each having a plurality of intercoupled flap leaves. According to the disclosure, the flap leaves and/or the flap units are activated individually, and an individual opening position of the respective flap leaves or of the flap units with the flap leaves is made possible.