The combination of swirl unit, newly developed air distribution element and innovative plenum box provides high volume flow rates, a low sound power level and low differential pressure. The air control blades of the swirl unit have three-dimensionally profiled contours to create an efficient swirl. Hence, the air velocity and temperature difference in the occupied zone are very low, and the level of comfort is excellent. A spigot with double lip seal provides a low leakage connection of the plenum box to the ducting, and a damper blade for flow rate balancing simplifies commissioning.