Motors and actuators are used throughout the HVAC industry, yet many technicians and building owners misunderstand how they differ and where each should be applied. Although both create movement, they serve distinct purposes in HVAC systems.
The Basic Difference
At the simplest level:
- A motor creates rotational movement
- An actuator creates controlled positioning (rotational or linear)
Both are essential components, but they operate very differently.
Motors: Designed for Continuous Rotation
A motor is engineered to spin continuously at high speed. In HVAC applications, motors are typically used to drive:
- Supply and return fans
- Blowers
- Compressors
- Pumps
Motors are selected and classified based on:
- Horsepower (HP)
- Revolutions Per Minute (RPM)
- Voltage
- Phase (single or three phase)
- Frame size (see NEMA motor standards)
Motors are built for constant rotation and high-speed operation, converting electrical energy into mechanical motion.
Actuators: Designed for Precise Positioning
An actuator is responsible for moving something to a specific position—and holding it there. Most HVAC actuators rotate a shaft within a limited range (often 90 degrees or less). Others provide linear motion (moving a rod in and out).
Actuators are used for:
- Economizer dampers
- Control dampers
- VAV (Variable Air Volume) boxes
- Fan coil units
- Unit ventilators
- Fan shutters
Actuators are not intended for continuous rotation. Instead, they move slowly and stop at precise positions determined by sensors or control signals.
Electrical Control of Actuators
Most HVAC actuators operate on 24VAC power and use analog control signals such as:
- 2–10V DC
- 4–20 mA
These control signals determine how far the actuator rotates or how much a damper opens. The actuator responds to sensors such as:
- Temperature sensors
- Mixed-air sensors
- Enthalpy sensors
This allows dampers or valves to modulate airflow or temperature based on real-time conditions.
Not All Actuators Use Electric Motors
While many actuators incorporate small motors, others rely on:
- Pneumatic pressure
- Hydraulic pressure
- Vacuum systems
These types are often found in older or industrial applications.
Dynamic Load vs. Static Load
When selecting an actuator, it’s critical to understand the difference between dynamic load and static load.
Dynamic Load
The force exerted on the actuator while it is moving.
Example: opening or closing a damper against air pressure.
Static Load
The force exerted on the actuator once it reaches its position and holds.
Example: maintaining a damper position under pressure.
Actuators are rated by torque (measured in foot-pounds), which must match the load requirements of the controlled device.
Why Selecting the Correct Component Matters
Choosing the wrong motor or actuator can result in:
- Equipment failure
- Safety hazards
- Reduced system efficiency
- Damage to dampers or fan systems
- Higher operating costs
Always replace components with the exact same specification and reference manufacturer documentation or industry standards, such as NEMA motor guidelines, when selecting a replacement.
