Compressor Controls and How to Enhance Compressed Air System Efficiency

The key difference is that compressor controls focus on the adjustments of individual compressors, while compressor systems involve coordinating multiple compressors to work together efficiently. Both are essential for saving energy and ensuring your system runs smoothly. 

System controls and compressor type selection are the most crucial factors affecting system performance and efficiency. Compressor technology has evolved to include start/stop, load/unload, modulating inlet control, and other controls, while electric motors and controllers have been developed to satisfy the demand for precise control. Special approaches are available for controlling multiple compressors in a system comprising fixed-speed and variable-speed drive (VSD) compressors.

There are several types of compressor controls available, including:

The start/stop control system turns on and off the motor driving the compressor in response to the discharge pressure and is best suited for low-duty cycles in the 25hp and under range. 

Load/unload control is suitable for almost any type of compressor and requires storage receiver volume, switching the compressor to unload at the unload pressure setpoint and returning it to full capacity once the lower load pressure is reached.  

Modulation, also known as inlet valve modulation, matches the compressor's capacity with air usage by throttling off the air inlet as pressure rises. However, this method can cause poor part load performance and requires significant air receiver storage.  

Dual control combines modulation and load/unload control to provide better part load performance and reduce storage receiver volume.  

VSD control adjusts the speed of the compressor motor to match air usage requirements precisely. This allows for better energy efficiency and part load performance, as the compressor can operate at varying speeds to meet demand. 

Network controls form a chain of communication between the on-board compressor controllers and coordinate compressor functions to optimize air usage. 

PLCs and HMIs are used for automatic processes, and variations in the speed of the driver can affect the compressor’s output. Compressor control systems have the ability to modulate the inlet valve, throttle gas intake, and maintain a certain pressure, ensuring that compressor output meets expectations. Automatic shutdowns can be initiated in the event of a component failure or unsafe working conditions. Networked controls are utilized in industries that need more than one compressor, with one compressor assuming the role of the master and the others taking on the functions of subordinates. 

The efficiency of an air compressor greatly depends on the control method used, and there are several methods available for various types of compressors. 

For oil-injected rotary screw compressors, the inlet valve modulation, also known as modulation, is one control method that matches the compressor's capacity with air usage by throttling off the air inlet as pressure rises. However, this method can cause poor part load performance and requires significant air receiver storage.

Load/unload control, on the other hand, is suitable for almost any type of compressor and requires storage receiver volume, switching the compressor to unload at the unload pressure setpoint and returning it to full capacity once the lower load pressure is reached.

Variable speed drive controls vary the speed of the motor and airend through a frequency drive to provide nearly proportional flow to power ratio at part load.

For centrifugal compressors, the blowoff valve and bypass valve are the traditional options for controlling air demand and surge while the unloading control reduces power consumption to 10 to 20% of full load power consumption.