Figure 7-42.Supply duct systems: A. Individual round pipe; B. Extended plenum; C. Reducing trunk; D. Multiple return air
Figure 7-43.Typical duct connections: A. Elbow; B. Tee: C.
Reducing tee; D. Cross: E. Lateral.
To enable a duct system to circulate air at the
proper velocity and volume to the proper conditioned
areas, you can use different components within the
duct system, such as diffusers, grilles, and dampers.
Diffusers, Grilles, and Registers
Room openings to ducts have several devices that
control the airflow and keep large objects out of the
duct. These devices are called diffusers, grilles, and
registers. Diffusers deliver fan-shaped airflow into a
room. Duct air mixes with some room air in certain
types of diffusers.
Grilles control the distance, height, spread of
air-throw, and amount of air. Grilles cause some
resistance to airflow. Grille cross-section pieces block
about 30 percent of the air. Because of this reason and
to reduce noise, cross sections are usually enlarged at
the grille. Grilles have many different designs, such as
fixed vanes which force air in one direction, or
adjustable to force air in different directions.
Registers are used to deliver a concentrated air
stream into a room, and many have one-way or
two-way adjustable air stream deflectors.