HVAC controllers
An HVAC (Heating, Ventilation, and Air Conditioning) controller is a device or system that manages and regulates the operation of heating, ventilation, and air conditioning equipment in buildings. Its primary function is to maintain a comfortable and controlled indoor environment while optimising energy efficiency. They exist in different formats: with or without a display, for wall mounting or for DIN-rail mounting, with a 3-button keyboard to set parameters or completely controlled via an online platform. They can control AC motors as well as EC motors.
HVAC controllers typically necessitate solution-specific firmware to ensure seamless integration and optimal performance within a particular heating, ventilation, and air conditioning system. Unlike generic, one-size-fits-all devices, these controllers are designed to meet the specific requirements of the HVAC infrastructure in a given environment. The firmware serves as the customised set of instructions that enable the controller to adapt to the intricacies of the system, including the type of equipment used, the building's layout, and the desired performance parameters. Due to the diversity in HVAC configurations and functionalities, a tailored firmware solution becomes essential for these controllers to function efficiently. This level of specificity ensures that the HVAC system operates in accordance with local building codes, energy efficiency standards, and the unique demands of the environment, providing not only comfort but also optimised energy consumption. Consequently, the need for solution-specific firmware underscores the importance of professional installation and configuration to achieve the desired performance outcomes.
What is an AC motor?
AC fans are fans with an asynchronous motor (AC motor). 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.
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.
Voltage controllable motors
Voltage controllable motors are AC motors of which the speed 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 AC motors are voltage controllable.
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.
What is an EC Motor?
EC fans are fans with an EC motor. An EC (Electronically Commutated) motor typically has a rotor of permanent magnets which rotates in (or around) the stator. The built-in fan speed controller generates an electric current in the stator windings, which can be more or less powerful depending on the 0-10V control signal. The electric current generates a rotating magnetic field, which the permanent magnets follow. This is how an EC motor runs.
What are the benefits of an EC Motor?
The main advantages of EC motors over AC motors are:
• High energy efficiency
• A long service life
• Reduced noise
• Relatively low electromagnetic interference (EMI)
The difference in energy consumption between an AC and an EC motor is clearly visible at reduced speed. At 20% speed, energy savings of around 70% can be achieved when compared to an AC motor. At nominal speed, energy savings of around 10 % can be achieved. The permanent magnets and the integrated electronics make this type of motor rather expensive. The higher purchase price is however compensated by its lower energy consumption.
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.
Minimise 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.