Variable fan speed controllers
Fan speed controllers are used to control the speed of various kinds of electric fans, such as centrifugal fans, extractor fans, propeller fans and axial fans. They reduce or increase fan speeds and thus slow down equipment wear and tear, decrease noise levels and save energy.
One type of fan speed controllers are variable or electronic fan speed controllers. This particular type of controllers regulate the revolutions of the fan, i.e. its speed, dynamically and provide infinitely variable control, which means fan speed can be set without any limitations between 0 and 100 % of the input voltage.
How do I chose the correct type of variable fan speed controller?
The key aspect is compatibility; you need a controller that is fully compatible with your fan type. This means you must check the voltage and amperage requirements and any other specific features or refer to your motor characteristics. If your fan is equipped with an AC motor and what you want is infinitely variable fan speed control, Sentera’s fan speed controllers are a wise choice.
TRIAC technology to reduce motor speed
Electronic or variable fan speed controllers offer infinitely variable speed control for AC fans. They use phase angle control, TRIAC technology, to reduce the motor voltage, which is how they control fan speed. TRIAC fan speed controllers can control motors with motor currents of up to 10 A. These fan speed controllers are completely silent, because the technology works with electronic components only.
TRIAC speed controllers reduce the mains voltage by cutting parts of it out. The remaining motor voltage will not have a perfect sinusoidal shape. Microprocessor control makes it possible to optimise the zero-cross detection. This means that the TRIACS can be controlled more accurately, resulting in a quiet motor operation. Nevertheless, depending on the motor type, some additional motor noise at low speed might occur due to the non-sinusoidal shape of the motor voltage. Increasing the minimum motor voltage will reduce the noise.
TRIAC speed controllers reduce the mains voltage by cutting parts of it out. The remaining motor voltage will not have a perfect sinusoidal shape. Microprocessor control makes it possible to optimise the zero-cross detection. This means that the TRIACS can be controlled more accurately, resulting in a quiet motor operation. Nevertheless, depending on the motor type, some additional motor noise at low speed might occur due to the non-sinusoidal shape of the motor voltage. Increasing the minimum motor voltage will reduce the noise.
What is an AC motor?
AC fans are fans in an AC motor. AC motors usually have a squirrel-cage rotor. Electric alternating current running through the stator windings generates a rotating magnetic field. This magnetic stator field induces currents in the rotor windings (Faraday’s law of induction). These electric currents in the rotor windings generate the magnetic field of the rotor. The two magnetic fields attract each other, causing the rotor to follow the rotating stator field. This principle makes an electric motor rotate.
AC motors have been the dominant motor in industrial applications and in the HVAC industry. Because of the wide range of variable speed drives and increasingly intelligent control solutions, the possible applications seem endless. AC motors are extremely reliable and very robust. They hardly require any maintenance and if they break down, they are easy to repair. AC motors are the industry standard and are therefore widely available in a very wide power range.
Voltage controllable motors
Voltage controllable motors are asynchronous motors, the speed of which can be controlled by reducing the voltage. When the nominal voltage is applied, the motor runs at high speed. When the motor voltage is reduced, the motor will slow down accordingly.
When the motor voltage decreases, the maximum motor torque also decreases. As long as the motor remains powerful enough to drive the load, the motor speed can be controlled by reducing the voltage. Note that not all motors are voltage controllable. Commonly used voltage controllable motor types are single-phase permanent split-capacitor motors or single-phase shaded pole motors.
Thermal protection for AC motors
An AC motor is a robust device with a long service life. However, operating an AC motor at low speed for a longer period of time is not without risks. At low speed, the motor cools itself less. This can cause overheating of the motor windings, which can cause degradation of its insulation. This can cause electric leakages, short circuits, and eventually, motor failure. To prevent motor failure, it is important to prevent the motor from being overheated.
For this purpose, many AC motors are equipped with thermal contacts, also called TK. These thermal contacts measure the temperature in the motor windings. In case of the motor overheating, the TK contacts open. Some fan speed controllers provide extra protection against overheating via their TK monitoring function, which deactivates the motor in case of overheating to prevent motor damage. At the same time, the alarm output will be enabled to indicate a motor problem.
Why do we need to control fan speed?
A motor at full speed is noisy, consumes much energy, costs money, and exacerbates heat losses. If we decrease fan speed, the motor will make less noise, will consume less energy, and this will, in turn, reduce the operational costs of the ventilation system. All this serves to increase the comfort of residents. Why would we not simply buy a smaller motor if that were the case? A motor needs to be at full capacity, like when there is a large crowd of people in a single room. A motor will also need to run faster when the temperature or relative humidity differs too greatly from the outdoors. In other words, to regulate the Indoor Air Quality, the motor and fan speeds need to be adjusted.
Energy savings - Another advantage of fan speed control is energy savings. If we would not control the fan speed, but instead let the motor run at full speed, there would certainly be a sufficient fresh air supply. But even a slight reduction in fan speed has a major impact on the electrical energy consumption of the fan. A typical HVAC fan follows a quadratic torque curve. Depending on the motor type, a reduction of 25 % air volume flow corresponds with 50 % less energy consumption. In addition, a lower air volume flow rate also results in a quieter operation.
Extended service life - Air filters last longer when reducing the air volume flow rate. This is logical; the more air that passes through the filters, the higher the risk of contamination of the filters. A reduced air volume flow rate also has a positive effect on the service life of the mechanical parts of the fan. These prolonged service intervals reduce the operational costs and the total lifetime cost.
Minimised heat losses - In colder and moderate climates, extracted warm indoor air is replaced by fresh air that can be much colder. That means that if we ventilate, we would need to spend more energy on heating. Modern ventilation systems are equipped with a heat exchanger to minimize such heat losses. Nevertheless, additional energy can be saved by reducing the fan speed when possible. By measuring the air quality of the indoor air, the fan speed can be continuously optimised while the indoor air quality is guaranteed.