Trane TRG-TRC014-EN Linear Slot Diffuser, Components of a VAV System, period two, Coanda, effect

period two

Components of a VAV System

notes

Linear Slot Diffuser

linear
slot	supply air
diffuser
Coanda	supply duct
effect	55°F [12.8°C]
air from
space	5 ft
	[1.5 m]

Figure 49

Linear slot diffusers are generally preferred for VAV air distribution. They use a principle known as the Coanda effect to distribute air to the conditioned space. The Coanda effect occurs when air is discharged at a relatively high velocity along the surface of the ceiling. This creates an area of low pressure that causes the supply air to hug the ceiling. As it travels along the ceiling, air from the space is drawn into, and mixed with, the supply air stream. When the air settles to the occupied levels of the space, it has reached an average temperature.

The design of linear slot diffusers allows them to effectively distribute air over a wide range of airflows, making them the preferred diffuser for VAV systems. They also offer acoustical benefits over other types of diffusers.

Proper selection and placement of linear slot diffusers generates air movement throughout the space, eliminating areas of stagnant and stratified air.

For applications with special air-coverage requirements, such as the

“blanketing” of an outside wall or window area, one-way discharge diffusers are commonly used. Such coverage is particularly useful for overcoming the downdraft problems that can occur when large volumes of heated air are distributed through ceiling diffusers.

34 TRG-TRC014-EN