How to Calculate a Damper Torque
A damper, also known as a zone damper, Volume Control Damper, VDC, or damper actuator, is a device that controls airflow in Heating, Ventilation, and Air-Conditioning, or HVAC, systems. HVAC systems are conventionally divided into different zones to improve the efficiency and comfort of the system. When you are in one zone and want it to be hot, dampers in the other zones close to direct the air to that zone. Zone dampers are generally electric, though they can use compressed air or vacuums in large-scale applications.
Acquire the Damper Torque Rating, or DTR, from the manufacturer for the damper at the most severe operating conditions. If you cannot get the DTR right away, use general estimates until you can get the actual rating. For standard leakage dampers, which is more than 10 cubic feet per minute per square foot (CfM/ft2), estimate 2.5 pound-inch/square foot (lb-in/ft2). For low leakage, 5 to 10 CfM/ft2, estimate 5 lb-in/ft2, and for very low leakage of less than 5 CfM/ft2, estimate 7 lb-in/ft2.
Calculate the area of the damper, or DA, by measuring the dimensions of the damper and multiplying the length by the height. The measurement should be in square feet.
Multiply the DRT by the DA to get the Total Damper Torque, or TDT.
Use a torque wrench on the shaft of the damper to acquire a measurement of the TDT if the DTR is not available.