Air Diffusers Glossary.

Primary Air
Primary Air is the conditioned air discharged by the supply terminal. This air provides the driving force for room air motion.

Total Air
Total Air is the mixture of primary air and entrained room air (air supplied under specific conditions from the supply terminal). The temperature differences between total air and room air creates a buoyancy effect which causes cold air to drop and warm air to rise.

Throw is the distance from the centre of the outlet face to a point where the velocity of the air stream is reduced to a specified velocity.

The drop of cool total air is the result of vertical spread of the air, and the buoyancy effect due to the density differences between the total air and the surrounding primary room air. Drop can be minimised by spreading air uniformly over the ceiling surface.

The spread is the distance the air stream branches out in a horizontal or vertical plane from its terminal device.

Coanda effect
The coanda effect is when the ceiling surface is used to reduce the drop of air.

Occupied Zone
The occupied zone is the area within 1800mm of the floor and not within 300mm of the boundaries of the walls. You should avoid drafts and temperature differences in this area.