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34 TRG-TRC014-EN
notes
period two
Components of a VAV System
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.
Linear Slot Diffuser
air from
air from
space
space
linear
linear
slot
slot
diffuser
diffuser
supply duct
supply duct
supply air
supply air
55°F
55°F
[12.8°C]
[12.8°C]
5 ft
5 ft
[1.5 m]
[1.5 m]
Coanda
effect
Figure 49