Damper actuator selection: torque, angle and fail-safe position
The first condition for saving energy in ventilation is that the damper actually closes — which comes down to torque selection.
Damper actuator torque is calculated from blade area (m²), damper type and leakage class using a torque figure per square metre. For low-leakage dampers this figure is markedly higher than for standard dampers. In addition to torque, rotation angle (typically 90°), running time, control signal (on-off, 3-point, DC 0–10 V) and the position taken on power failure (spring return or not) must be defined.
The cost of under-specifying torque
A damper driven with insufficient torque never fully closes. Air leaking through a fresh air damper that should be shut in winter raises the heating load and creates a freezing risk. This leakage often goes unnoticed because the position indicator reads "closed".
Deciding the fail-safe position
A spring-return actuator drives the damper to a predefined position on power failure. Closed is typical for fresh air dampers needing frost protection, open for smoke exhaust. For comfort-oriented mixing dampers it is usually unnecessary.
Frequently asked
Can one actuator drive more than one damper?
It is possible with a linkage, but total torque demand and losses in the linkage must be accounted for. In practice separate actuators are more reliable.