Incorrectly installed or broken damper actuators can cause ductwork dampers to open only partially or not at all. This, in turn, can lead to comfort complaints, cold/hot rooms, and possible IAQ problems.
That’s why it’s important to specify or install the correct actuators in the first place, or look to them as a possible problem source when troubleshooting commercial systems, according to Mike Wolf, a sales manager for Greenheck, Schofield, Wis. The company makes and markets fans, dampers, and other air-moving products.
Choosing and installing the correct damper in the first place means winning more than half the battle.
Manual, Pneumatic, Or Electric
“If the damper is required to operate automatically as part of an HVAC system, an electric or pneumatic actuator should be provided,” he said.
There are often several trades involved with the selection and installation of the damper and actuator. For example, the sheet metal contractor may order and install the damper, an electrician or pipe fitter connects power to the actuator, and a temperature control contractor may connect control sequencing to the damper. In this scenario, the power source must be confirmed with the electrician or pipe fitter and the control signal confirmed with the temperature control contractor.
Electric actuators are not inherently fail-safe, Wolf noted. “For fail-safe operation, spring-return models may be specified.”
How Will It Function?When choosing damper actuators, the temperature controls contractor also needs to consider how the damper will operate in the system, Wolf said. For instance, contractors should ask themselves the following questions:
Installation“A lot of things can go wrong” in actuator installation, said Wolf. Incorrect location is one potential trouble spot, particularly if the actuator will be installed in the field.
According to Wolf, external mounting may require that the damper be furnished with a sleeve or side plate, so that the unit can be mounted externally to the ductwork, out of the airstream.
The advent of direct-coupled actuators has made installation easier in situations where linkage hookups had been used before, Wolf said. “Older models with linkage hookups were often installed incorrectly,” he commented.
These types of situations could result in dampers that may not open or close fully, he said. In addition, it is possible to connect the actuator so the damper closes and opens properly but the actuator does not rotate through its entire rotation. When this occurs, some actuators fail to engage a stall winding at the end of the stroke, causing the actuator to continue to draw full power and burn out. This would result in damper malfunctioning. And this, naturally, results in comfort problems and tenant discomfort.
“Most of the time, contractors find out there is a problem with an actuator when somebody isn’t getting enough heat or cooling,” Wolf explained. If the problem is detected during the system repair, or even during regular maintenance or building recommissioning, this is a good time to replace the linkage hookup actuator with a direct-coupled model.
TorqueIn operation, an actuator must deliver a specific amount of torque to position the damper accurately. This is rated in inch pounds (in.-lb). A damper’s torque requirement is usually expressed in inch pounds per square foot (in.-lb/sq ft).
“The actual torque required to operate a damper is affected by a number of factors,” Wolf stated, “some of which are under the damper manufacturer’s control — but some are not.” For example:
“How the damper is installed in the ductwork and how the actuator is installed can have a significant affect on torque requirements,” said Wolf. “Dampers installed twisted or out of square may require many times more torque than dampers installed square and plumb.” (Some manufacturers, such as Greenheck, have designs to prevent such problems, as much as is possible.)
Select a damper actuator with a rated torque that is greater than the damper’s required torque, advised Wolf. If you select an actuator that uses crank arms and linkage rather than the direct-couple connection, the company recommends an additional safety factor of 30 to 50 percent. “When in doubt, the next larger size actuator is always the safest choice,” said Wolf.
Last WordsThere are additional selection considerations, such as NEMA enclosure ratings and accessories, such as auxiliary switches. Furthermore, due to system and design modifications, and/or missing documentation, you might not have all the information you need to make the best selection.
“The actuator selection process is not a simple one,” Wolf said. “Often the information necessary to select the appropriate actuator is not available. Unfortunately, this can result in improper actuators being furnished, causing confusion and extra cost.”
When in doubt, contact the manufacturer to determine the best actuators for the dampers in your project, he concluded.
For more information, Wolf may be contacted at 715-359-6171.
Publication date: 07/28/2003