Henri Coanda was a Romanian inventor and engineer who contributed many ideas to the field of aeronautics. He spent some 20 years investigating the phenomenon that now bears his name.
When a jet is brought close to a flat or convex surface lying in parallel, the jet itself is attracted to the surface and stays close to it. It creates a zone of low pressure on the opposite side of the surface, which encourages entrainment of the medium present there.
AirMaster wall-mounted heat recovery ventilation units use the Coanda effect to distribute incoming air across a room. The inlet grille is placed as close as possible to the ceiling line, and care is taken to ensure that the ceiling in front of the MVHR unit is flat and clear of any obstruction which may deflect the air pathway. AirMasters deliver inlet air to the room typically at 19ºC, at a velocity of 3 – 4 m/sec. This air stays close to the ceiling for a throw of between 5 and 8m, depending on the model in question. As it moves across, this air jet entrains room air from below and is gently brought up to room temperature by the time it reaches the back of the room. There is a corresponding drop in air velocity, so that as the jet begins to fall away, it is moving at no more than 0.1-0.2 m/sec. This is how AirMaster MVHR units deal with the problem of wintertime draught.