Damper Flow

A damper is a mechanical device in a duct or chimney that regulates airflow. More specifically, it’s a valve or plate that stops or regulates the flow of air inside a duct, chimney, Variable Air Volume (VAV) box, air handler, or other air handling equipment.

Zone Damper

Zone Damper

A damper is sometimes used to cut off central air conditioning (heating or cooling) to an unused room, or to regulate it for room-by-room temperature and climate control. Its operation can be manual or automatic. Manual dampers are turned by a handle on the outside of a duct. Automatic dampers are used to regulate airflow constantly and are operated by electric or pneumatic motors, in turn controlled by a thermostat or building automation system. Automatic or motorized dampers may also be controlled by a solenoid, and the degree of air-flow calibrated, perhaps according to signals from the thermostat going to the actuator of the damper in order to modulate the flow of air-conditioned air in order to effect climate control.(source)

Automated zone dampers

A zone damper (also known as a Volume Control Damper or VCD) is used specifically to control the flow of air in an HVAC heating or cooling system. HVAC systems are typically divided up into multiple zones.  This will allow users of the system to direct heat or cool air to areas high occupancy areas, allowing the unoccupied areas to cool down. Doing this will improve efficiency and occupant comfort.

Zone dampers as used in home HVAC systems are usually electrically powered. In large commercial installations, vacuum or compressed air may be used instead. In either case, the motor is usually connected to the damper via a mechanical coupling.

There are 2 main types of electrical zone dampers:

  1. The motor is often a small shaded-pole synchronous motor combined with a rotary switch that can disconnect the motor at either of the two stopping points – “damper open” or “damper closed”. In this way, applying power to the “open damper” terminal causes the motor to run until the damper is open while applying power at the “close damper” terminal causes the motor to run until the damper is closed. The motor is normally powered from the same 24 volt ac power source that is used for the rest of the control system. Doing this allows the zone dampers to be directly controlled by low-voltage thermostats and wired with low-voltage wiring. This style of damper is often designed to only obstruct a portion of the air duct, for example, 75%. It is important to note that simultaneous closure of all dampers might harm the furnace or air handler.
  2. Another style of electrically powered damper uses a spring-return mechanism and a shaded-pole synchronous motor. These dampers are normally opened by the force of the spring but can be closed by the force of the motor. Removal of electrical power re-opens the damper. With these dampers,  if the control, the damper opens and allows air to flow. These dampers will also allow adjustment of the “closed” position so that they only obstruct, for example, 75% of the air flow when closed.
Air foil control damper

Air foil control damper

For vacuum-operated or pneumatically operated zone dampers, the thermostat usually switches the pressure or vacuum on or off, causing a spring-loaded rubber diaphragm to move and actuate the damper. As with the second style of electrical zone dampers, these dampers automatically return to the default position without the application of any power, and the default position is usually “open”, allowing air to flow. Like the second style of electrical zone damper, these dampers may allow adjustment of the “closed” position.

Highly sophisticated systems may use some form of building automation such as BACnet (building automation and control networks) or LonWorks (local operating network) to control the zone dampers. The dampers may also support positions other than fully open or fully closed and are usually capable of reporting their current position and, often, the temperature and volume of the air flowing past the smart damper.

Damper systems are often designed so that when no thermostat is calling for air, all dampers in the system are opened. This allows air to continue to flow while the heat exchanger in a furnace cools down after a heating period completes.