What is an electric motor?
An electric motor is a device that converts electrical energy into mechanical one. This occurs through the interaction of a magnetic field and electric current in the motor's windings (coils), which produces a force, or torque, on the motor shaft. The motor consists of two main parts: the rotor, which moves, and the stator, which remains stationary. In most traditional AC motors, the windings are located in the stator. When alternating current flows through the stator windings, it creates a rotating magnetic field. The rotor’s magnetic field follows this rotating stator field, causing the motor to spin.
Asynchronous motors typically feature a squirrel-cage rotor, where the rotating magnetic field of the stator induces currents in the rotor windings, according to Faraday’s law of induction. These currents in turn generate the rotor’s magnetic field. In contrast, synchronous motors often have rotors with permanent magnets, which directly follow the rotating stator field.
Positive and negative sides of using variable frequency drives in HVAC industry
In some applications (such as robots on production lines, medical equipment, laboratory instruments and similar) the precise speed control is crucial for both keeping the quality of the installed fans and control devices, and for delivering precisely measured ranges of temperature, relative humidity and others in order to take on-time actions to preserve the comfort of inhabitants. Frequency inverters can provide highly accurate speed control, enabling precise operations and production in these applications. The primary advantage of a frequency inverter lies in its ability to enhance energy efficiency and optimize motor performance. By dynamically adjusting the motor's speed to match the actual requirements of a task, a frequency inverter prevents unnecessary energy consumption. This is particularly beneficial in applications where the load changes dynamically or when a constant speed is not essential, such as in heating, ventilation and air conditioning systems.
Moreover, frequency inverters extend the lifespan of motors by reducing wear and tear associated with abrupt starts and stops. They also provide precise control, improving the overall accuracy and quality of processes. In industrial applications, where electric motors play a crucial role, integrating frequency inverters contributes to cost savings, environmental sustainability, and more reliable operation of machinery. In essence, a frequency inverter is like a smart accelerator for electric motors, offering flexibility, efficiency, and longevity.
The major difference between a frequency converter and a fan speed controller is not easy to explain in non-technical terminology. Here's an attempt anyway. A frequency converter offers optimal motor control because it can regulate not only the voltage, but also the frequency. This has the advantage that the motor can be controlled much more efficiently and accurately. Disadvantages of this technology are its complexity and price. A fan speed controller can only regulate the motor voltage. This is done simply by cutting away parts of the supplied voltage with TRIAC technology (phase angle control). The advantage of this is that fewer expensive electronic components are required and that the device can be put into use immediately. A frequency controller must first be configured before it can be put into use.
Negative sides - Electromagnetic pollution
Electromagnetic pollution caused by frequency inverters refers to the unintended electromagnetic interference they may generate, potentially affecting nearby electronic devices and communication systems. This interference can manifest as disruptions, glitches, or malfunctions in radios, TVs, and other sensitive equipment. The risks associated with electromagnetic pollution include compromised performance and reliability of nearby electronic devices, which may be critical in residential or industrial settings.
To avoid these issues, it is crucial to implement mitigation measures. The electromagnetic compatibility (EMC) filters that are standard integrated in our frequency inverters, help to suppress electromagnetic interference, preventing it from radiating into the surrounding environment. Proper grounding and shielding of cables also play a role in minimizing electromagnetic pollution. Installation practices, such as maintaining appropriate distances between sensitive equipment (e.g. data cables, analogue signals, communication cables, etc.) and potential sources of electromagnetic pollution (e.g. power cables, electric motors, frequency inverters, etc.) can further reduce the risk of interference.
Pulse Width Modulation for optimal motor control
Frequency inverters, also known as Variable Speed Drives, provide precise speed control for AC fans through infinitely variable adjustments. Similarly, as described earlier, electronic fan speed controllers offer this capability too. What divides them apart? A frequency inverter employs Pulse Width Modulation (PWM) with IGBT technology to regulate both motor voltage and frequency. This method ensures exceptionally quiet motor operation and nearly perfect sinusoidal motor voltage under all conditions. Depending on its settings, a frequency inverter can operate silently itself.
However, because a frequency inverter switches between direct current and alternating current frequently, it can introduce electromagnetic interference (EMC) to other devices on the same power grid. Expensive specialized filters have been developed to mitigate this EMC pollution. Moreover, frequency inverters generally involve higher initial configuration costs due to their inherent complexity compared to other fan speed controllers. In summary, while frequency inverters are more costly and complex to set up, potentially requiring additional tools, they offer extremely precise motor control. These controllers are highly energy-efficient and capable of handling substantial motor currents.
The requested motor speed can be adjusted via the controls that are integrated onto the device itself (potentiometer or push buttons). It is also possible to adjust the motor speed remotely via Modbus RTU or an analogue control signal (e.g. 0-10 Volt signal).
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.
Positive sides from regulating the 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 – The fan speed must be constantly monitored and controlled in order to have sufficient fresh air supply! But even a slight reduction in fan speed might cause a major problem - the electrical energy consumption of the fan grows bigger. 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 - 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.
Reducing heat losses - In colder 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.
How to connect to SenteraWeb?
In order to connect your frequency drive to the SenterWeb HVAC cloud platform to configure, add new information or just to monitor the measured values and to receive on-time notifications in case of trouble, you’ll need the ADPT-3SM-FI adapter. This adapter is used to facilitate the connection between the frequency inverter and your computer. Just install the drive, add your basic information in your profile in the SenteraWeb platform and start monitoring your installation.
For further information over the different types of frequency inverter, go to the product category on the website. To see different examples of combining and installing frequency inverters, check the solutions category on www.sentera.eu/solutions.