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Temperature-based fan speed control for AC motors

04/09/2023 An De Ridder

We need controls and control systems because, in our modern age of technology, they make our lives more convenient, comfortable, efficient and effective. HVAC controls enable equipment to operate effectively and sometimes give the ability to change their actions as time goes by and conditions or occupancies change.

Temperature-based fan speed control for AC motors
The choice of controller type is important. Opting for manual control means you and not a device are acting as the controller - you make the decisions about what control actions to take.  Automatic control imitates the actions you would take during manual control. The reason we use automatic controls is that we do not have the time or desire, or perhaps the ability, to constantly monitor a process to maintain the desired result.

Temperature is a major factor in comfort ventilation and is readily measured and controlled. HVAC systems are generally designed to handle peak cooling or heating loads that seldom, if ever, take place, so we must provide controls that can regulate the system’s output to meet the actual cooling or heating load at a given time.

If you have a voltage controllable AC-motor, and want to control fan speed based on temperature, we can offer our brand new GTH21-series. The controller is available in 7,5 A and 10 A and is an extension to our already well-known GTH-1-series. The functionalities are the same but the electronics used are newer and it has Modbus RTU communication, which our GTH-1 does not have.

Below is a list of the most important characteristics of our GTH21:
1.    Transformer technology: It is highly reliable and durable, producing a motor voltage with a smooth sinusoidal waveform. This results in exceptionally quiet motor operation and an extended service life.
2.    Temperature-based control: The GTH21-series offers the ability to control single-phase motors in five steps based on the measured ambient temperature. The PT500 temperature probe is connected directly to the controller and placed in the desired area, thus optimising the motor speed for efficient operation depending on the environmental conditions. Motor speed is controlled by varying the output voltage.
3.    Heating or Cooling mode: In heating mode, the fan is activated when the measured temperature drops below the set temperature. When the measured temperature is higher than the selected temperature, the fan is deactivated. In cooling mode, the functionality is inversed. You can switch between modes by using a jumper. 
4.    Automatic and manual control: The controllers come with both automatic and manual modes, giving users the flexibility to choose between automated temperature-based control and manual adjustment.
5.    Voltage output variation: The controllers regulate the rotational speed of single-phase voltage controllable motors by varying the output voltage in accordance to the measured ambient temperature. This dynamic adjustment helps maintain optimal performance based on changing conditions.
6.    Relay output or unregulated output for valve control: The device is equipped with a relay output that responds to the measured temperature. This output can be utilised to control a valve, making it suitable for use in both cooling and heating systems. This capability contributes to maintaining consistent temperature levels.
7.    Modbus compatibility: The GTH21 controllers can be fully controlled using the Modbus protocol. Modbus is a common communication protocol, allowing for seamless integration and remote management.
8.    Enclosure and protection: The controllers' enclosure is made of sheet steel, providing a robust and durable housing. The enclosure's IP54 protection rating ensures resistance against the ingress of water and dust, making the controllers suitable for various environments.
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