When supply air is introduced at high level it ‘attaches’ to the ceiling because of a phenomenon known as the Coanda effect. The result is that the air travels across the room and falls gently across the entire space, rather than falling immediately after entering the room and creating a draught (as would be the case if it were introduced at lower level). Consequently, exploiting the Coanda effect by positioning ventilation units at high level ensures good distribution of the supply air and prevents uncomfortable draughts.

Another beneficial effect of the Coanda effect is that the required air distribution can be achieved with lower air velocities and fan power consumption.

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