One way of getting even air distribution is through
the use of duct dampers. Dampers balance airflow or
can shut off or open certain ducts for zone control.
Some are located in the grille, and some are in the duct
itself. There are three types of dampers used in
air-conditioning ductworkbutterfly, multiple blade,
and split damper (fig. 7-44). When installing a damper,
always draw a line on temperature control.
Automatic fire dampers should be installed in all
vertical ducts. Ducts, especially vertical ducts, will
carry fumes and flames from fires. Fire dampers must
be inspected and tested at least once a year to be sure
they are in proper working order. There are two types
of fire dampers, which are fail-safe units
spring-loaded to close and weight-loaded to close. Fire
dampers are usually held open by a fusible link. Heat
will melt the link and the damper will close by either
gravity, weights, or springs (fig. 7-45).
Air movement is usually produced by some type of
forced airflow. Fans are normally located in the inlet of
the air conditioner. Air is moved by creating either a
positive pressure or negative pressure in the ductwork.
The two most popular types of fans are the axial flow
(propeller) or radial flow (squirrel cage) (fig. 7-46).
Figure 7-45.Fire damper in OPEN position.
Figure 7-44.Three types of duct dampers.
Figure 7-46.Principal types of fans: A. Radial flow; B. Axial