EC fan speed control

EC fans

EC fans are powered by brushless DC motors. These motors are also known as Electronically Commutated motors or EC motors. A typical EC motor has a rotor of permanent magnets which rotates in (or around) the stator. The built-in fan speed controller generates electric current in the stator windings. This electric current generates a rotating magnetic field. The permanent magnets follow this rotating magnetic field and the motor runs.

The control electronics (fan speed controller) are always integrated in the EC motor since this motor type requires a coordination between rotor position and motor currents. Without this coordination, it would not be possible to start up the motor. This integrated fan speed controller converts the mains (AC voltage) into a DC voltage that is required to control the motor.

Next to the mains (230 VAC power supply), it requires a control signal that specifies the requested fan speed. This control signal can be digital (Modbus RTU communication) or analogue (typical 0-10 Volt). The control signal can be generated manually via a control switch (in steps) or via a potentiometer. It can also be generated by an HVAC sensor or an HVAC controller. In that case, demand based fan speed control is possible.

The main advantages of EC motors are:

  • High energy efficiency
  • A long service life
  • Reduced noise
  • Relatively low electromagnetic interference (EMI)
EC fans inside

The difference in energy consumption between an AC and an EC motors is clearly visiblee at reducd speed. At nominal speed, energy savings around 10 % can be achieved.

However, the permanent magnets and the integrated electronics make this type of motor rather expensive. The higher purchase price is compensated by its lower energy consumption.

How to control EC fan speed?

Since EC fans have a built-in fan speed controller, they just require a control signal that defines the requested fan speed. The type of this control signal depends on the EC motor type. Typically this is an analogue 0-10 V signal but more and more EC fans are available with Modbus RTU communication. The control signal can be created manually or automatically.

If you want to control fan speed manually, the control signal can be generated via:

Intelligent HVAC sensors
  • Control switch - A control switch generates a 0-10 Volt signal in steps. The advantage of control switches is that a limited number of predefined fan speeds can be selected easily.
  • Potentiometer - This is a device to generate a continuously variable 0-10 V control signal. Potentiometers are available with or without OFF position. The control signal can be generated from high to low (10 – 0 Volt) or from low to high (0 – 10 Volt)

If you want to control fan speed automatically or demand based, the control signal can be generated via:

  • Intelligent HVAC sensors - Typically used to control extraction fans or ceiling fans. A standard HVAC sensor or HVAC transmitter measures certain values like temperature, humidity, CO2, air quality, etc. The measured values are transmitted via analogue outputs or via Modbus RTU communication. Intelligent HVAC sensors have one output. This output is controlled by an intelligent algorithm. The output controls fan speed to keep one or more parameters within range. E.g. if fan speed needs to increase when CO2 or humidity levels are too high, an extraction fan can be controlled via an intelligent CO2 – humidity sensor. The intelligent sensor’s output controls the EC fan or AC fan speed controller. Fan speed will increase when CO2 or humidity level are increasing. More information about HVAC sensors can be found on www.air-quality-monitor.eu.
Intelligent HVAC sensors
HVAC controllers
  • HVAC controllers - To control a complete ventilation system, Heat Recuperation Unit or Air Handling Unit, the market offers universal controllers which have to be programmed. Depending on the connected devices, this can be reasonably to very complex. However, full-range manufacturers also offer complete, turn-key solutions that are often more efficient as the complex universal HVAC controllers. Since these HVAC control solutions are made for a specific application, they are usually very user-friendly, intelligent and easy to install.