Customized and reliable stepper motors address HVAC damper application extremes

In any HVAC (heating, ventilation and air conditioning) system, dampers are used to control the airflow in the ducts. In some systems, manual dampers can allow personnel to turn a lever on the outside of a duct. But if you need to constantly control the airflow, you need automatic valves with electric or pneumatic motors that can be controlled by a thermostat or a building automation system.

Krishna Kumara
Manager, product design and development
and
Amol Ridhore
Chief Engineer and Materials Technologist
Portescap


When designing a remote mounted electric damper actuator for an HVAC system, keep in mind that not all miniature motors are created equal. It is important to consider the different conditions that HVAC systems provide and how they can be addressed to create the best combination of motor and muffler.

commercial HVAC system
An HVAC system in a commercial building

Electric damper rotary actuators generally fall into three categories:

  • Spring return: A spring allows the damper to return to the desired closed or open position.
  • Non-spring return: The damper maintains its existing position in the event of a power failure.
  • Electronic fail safe: Supercapacitors discharge stored energy to the motor and the actuator is driven open or closed in the event of a power failure.

Depending on how often they are needed, damper actuators can be further classified: two-position control or modulating for more precise control. For occasional use, manual control with two positions is the best option. For frequent or daily use, an automated electric damper with electric motors is ideal.

stepper motor damper actuator
An external mounted electric damper actuator

When evaluating a miniature motor to interface with an actuator, keep in mind that it may need to be modified. Ask yourself the following questions:

  • How much torque and force must the motor-linear actuator combination provide to hold the damper in place with the required control accuracy?
  • Can the engine withstand extreme temperatures?
  • Can the motor components be modified to withstand HVAC cycles?
  • Does the motor provide the position feedback required by the integrated damper?

Rotor design for extreme temperatures and cyclic loading

For custom stepper motors used with damper actuators in HVAC applications, rotor design is critical. Inside the damper actuator, the motor will start and stop under varying thermal conditions, putting additional thermomechanical stress on the rotor and other internal components. The non-linear material used in rotors must have certain thermal properties – especially belonging to the coefficient of thermal expansion (CTE) – in order to operate reliably at extreme temperatures.

stepper motor damper actuator
Stepper Motor Cross Section

Choosing linear and nonlinear material-based assemblies can be challenging because the performance of nonlinear materials, such as adhesives, is dependent on material chemistry and processing parameters. In addition, certain types of ceramic magnet make the decision even more difficult.

stepper motor rotor forces
Forces acting on the rotor assembly

Design validation through qualification testing

Be sure to validate your design by verifying field performance under static environmental conditions such as temperature and humidity or specific load conditions. The material scheme you have chosen already takes these conditions into account. However, their performance under dynamic conditions that may be accompanied by rapid temperature, humidity or sudden load changes, or combinations of multiple factors, must be validated through simulations or analytical tests to determine long-term engine performance.

For example, at Portescap, we validate rotor assemblies at accelerated temperatures and thermal shock in environmental chambers and furnaces to confirm that a rotor assembly will meet the extreme requirements of the application. We also perform axial and torsional tests to determine the mechanical strength of the rotor at a specific temperature requirement, as well as accelerated life tests to predict the life of a motor in its application under specific test conditions. The tests are performed under loaded and unloaded conditions, depending on the application requirement.

stepper motor damper actuator
Accelerated thermal cycle of a stepper motor

Customized reliable stepper motors can meet your needs

Stepper motors are a good technology choice for use in electrically operated dampers. They are more affordable than brushless DC motors, and typical HVAC damper applications don’t need the latter’s superior variable speed capability.

The right stepper motor is critical to efficient airflow control in HVAC systems. Therefore, you have to choose from a wide variety of stepper motors with different configurations. Stepper motors offer the HVAC valve actuator market an attractive price-performance ratio, and Portescap offers custom stepper motors to ensure you meet your needs. Don’t forget to communicate your application requirements to your stepper motor partner so they can help you address them during the critical design and validation phases.


Filed Under: Motion Control Tips


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