Zone control of a forced air system is done with a thermostat for each zone. The thermostat
signals a control panel, which in turn opens the corresponding zone damper and turns on
the appliance (furnace, air handler etc.). Some older zoned systems do not use a control
panel. The thermostat controls the damper, and the damper has trip switches that turn the
appliance on (similar to zone valves in a hydronic system).
The control panel is necessary for modern systems to control the change-over from heating to cooling and vice-versa. The control panel also allows for selection of normally open or normally closed positions of the dampers for purging after the thermostats are satisfied.
Dampers come in a variety of designs. Opposed blade dampers use a motor to open and close them. This damper design has the appearance of accordian or folding panels when closed, and metal slots when open.
Single blade dampers can use a motor to open and close them, or use a spring to close them and a motor to open. This type will remain in the closed position at rest. A single blade with spring open uses the motor to close, and is open at rest.