What is a damper?
A damper is a valve or metal plate that blocks or adjusts the flow of air inside a duct, chimney, BOX VAV, air conditioner or other air control (adjustment) equipment. A damper can be used to shut off the central air conditioning system (heating or cooling) in a room that is not in use, or to adjust the temperature and control the air from one room to another.
Their operation can be manual or automatic. Manual dampers are rotated by a handle on the outside of the duct. Automatic dampers are used to regulate air flow in fixed amounts and are operated by electric or pneumatic motors, which are controlled by a thermostat or building automation system.
Automatic or motorized dampers may also be operated by a solenoid (a solenoid is a cylindrical coil that is usually longer than its diameter, and when an electric current passes through it, a magnetic field is produced, and according to Lenz’s law, by changing the amount of current in It resists the flow change.) and the air flow angle is calibrated by signals such as the signals that go from the thermostat to the actuator (actuator) of the damper in order to adjust the air flow and control the environmental conditions of that space.
In a flue, the damper closes the pipe to prevent cold or warm outside air (and birds and other animals) from entering. This practice usually takes place in the summer, but is sometimes used in the winter as well. In some cases, the damper is also partially closed to help control the amount of combustion. Access to the damper may be via a handle or heater stick, or sometimes by a lever attached to the bottom or outside. This is in a wood-burning stove or similar device, usually located in the exhaust duct of an air conditioning system. If you forget to open the damper before lighting the fire (starting a fire, heat), this can cause a serious risk of smoke entering the house and even a house fire.
Channel dampers
Duct dampers (also known as volume control dampers or VCDs) are a special type of damper used to control airflow in an HVAC heating or cooling system. In order to improve the efficiency and comfort of the occupants, air conditioning systems are usually divided into multiple zones. For example, in a home, one district heating system may be used on the main floor while another system serves air conditioning in the upstairs bedrooms. In this method, the heat is basically directed to the main room during the day and to the bedrooms at night, allowing the empty spaces of the house to be cool. (Keep the temperature low in the empty spaces of the house.)
Duct dampers used in home air conditioning systems are usually powered by electricity. In large commercial installations, vacuum or compressed air may be used instead. In each of these cases, the motor is usually connected to the damper through a mechanical coupling
Advantages and disadvantages of channel dampers
Advantages: low cost and power consumption
Cons: Dampers must be permanently accessible through ceiling access panels due to new US residential building codes.
Channel dampers are not 100% reliable. Most models of automatic dampers that operate with electric motors are not designed to go to a safe condition in the event of a problem. Although the automatic dampers which are normally open move to the safe condition i.e. open in the trouble mode
Types of designs of channel dampers
In one design, the motor is often a small synchronous motor in combination with a rotary switch that can stop the motor at either of two stop points (“damper open” or “damper closed”). In this method, connecting the voltage to open the damper causes the motor to start and run when the damper is open, while connecting the power to close the damper causes the motor to remain closed while the damper is closed. This motor is usually powered by the same 24 volt AC power source that is used in the control system. In this method, channel dampers are allowed to be directly controlled by low voltage thermostats and wired at low voltage. In this method, closing all the dampers at the same time may damage the furnace or the holding air, from this model, the dampers are often designed to block the duct, for example, up to 75%.
Another model of electric damper uses a return spring mechanism and a synchronous motor. In this case, the damper is normally opened by the force of the spring and closed by the force of the engine.
Another model of channel dampers uses a ceiling spring and motor. In this case, by removing the electric power, open the damper again. This model of dampers is very useful because the damper is placed in a safe condition in case of failure; If there is a problem in the damper control, the damper is not opened and the air flows. However, most of the uses of this model of dampers are such that the damper closes as soon as the electricity is removed, thus preventing the spread of smoke and fire to other areas. Also, in these dampers, the degree of closure can be adjusted so that, for example, they block 75% of the air when they are closed.
To pneumatically actuate (activate) channel dampers, the thermostat usually creates a load in the spring rubber diaphragm by changing the pressure and activates the damper. Like Type II duct dampers, these duct dampers return to the default position without applying any force, and the default position is usually open, allowing air to flow. Like the second type of electric dampers, in this type of dampers, a better position can be adjusted. In very complex systems, building automation types such as BACnet or LonWorks can be used to control regional dampers. Dampers can also support other positions other than completely open or closed and are usually able to report their current position as well as the temperature and volume of air flow passing through smart dampers.
Regardless of the type of damper used, systems are often designed so that all dampers in the system open if no thermostat is active. This allows the heat exchanger in a furnace to be cooled by air flow after a complete heating period
Comparison of multiple furnaces / aerators
Multiple zones can be operated as separate zones using individually controlled furnaces/air handlers or single furnace/air handlers with multiple channel dampers. Each approach has advantages and disadvantages.
Advantages:
Mechanical design and simple control (“SPST thermostat”)
Redundancy: If one part of the furnace fails, the others can continue to work.
Disadvantages:
Cost: Furnaces will cost much more than ducted dampers.
Power consumption: Operating furnaces constantly consume power, while a ducted damper only consumes power when moving from one position to another. (or in some cases, a very small amount of power while the holder is closed)
Fireproof dampers
Fire dampers are installed in areas where the duct passes through the walls of the fire compartment (fire separator) / fire wall as part of the fire control strategy. Under normal conditions, these dampers are kept open using fuses. When the dampers are exposed to heat, these fusible links melt and allow the dampers to be closed using a spring. Fuses are connected to dampers, dampers can be tested manually.
