How PID can cut energy usage in HVAC applications
External PID controllers and PLCs can be expensive or complex to install and operate. Oliver Woolley, ABB’s key account manager for HVAC, explains how a drive’s integrated PID function can help to save energy in HVAC applications.
PID loop control is a tool in a drive’s arsenal that uses precision control to maintain specified set-points, helping to ensure that the drive controls a system as efficiently as possible, without needing an external controller. Applications can include AHUs, chilled water pumps and cooling tower fans, all of which are variable-torque applications with the potential to save energy and optimise applications using variable-speed control.
The most capable modern drives have two PID control loops built in. A set-point reference can be connected directly to the drive instead of a speed reference, and an actual value feedback signal is also connected directly to the drive. The PID control adjusts the drive speed to the motor to keep the actual value at the desired set-point.
Some drives manufacturers also offer sleep and boost functions for PID-controlled applications, where consumption varies. For example, this function can be used in a pump application. When consumption drops, the drive’s built-in PID control function reduces the motor speed. The sleep and boost functions can be used to stop the pump during low demand, instead of running the pump slowly below its efficient operating range.
The sleep function detects the motor’s slow rotation and stops unnecessary pumping after the sleep delay has passed. The sleep mode is activated while still monitoring the system pressure via the actual value feedback signal. Pumping resumes when this pressure falls below the predefined minimum level and the wake-up delay has passed. PID sleep time can be extended using the drive’s boost function, thus increasing the set-point for a predefined time before the drive enters sleep mode.
PID “wizards” are becoming more common in the latest generation of drives, taking all the complexity out of programming PID control.
For a step-by-step guide on configuring PID control on an ABB ACH580 drive, you can watch this video: https://www.youtube.com/watch?v=yGOoAw8DYQs
