An electronic controller / PLC for operation of multiple compressors of equal or different capacities in a single pressure band to start / stop or load / unload / capacity variation based on intelligent algorithm to manage in most energy efficient manner.
A properly tuned master controller ensures that the supply side (air compressors) automatically and most efficiently follows compressed air demand in the plant. The control algorithm is based on ‘rate of change’ of pressure than just pressure. It can intelligently utilise different capacity compressors as well as different types of capacity control mechanisms of compressors to match supply to demand. It is programmed to choose most appropriate capacity compressor between available compressors: if a large compressor would be more efficient, then it would be started; if only a smaller capacity compressor was required, it would come online. In this way the system would be flexible enough to compensate for changing loads and compressors availability.
This becomes more complex in case of Centrifugal compressors or combination of positive displacement and dynamic displacement compressors. This needs continuous monitoring of various parameters (pressure, Amps, interstage temperature etc.) either to operate a base load compressor very close to their surge points on their performance curve or use equal modulation on all compressors depending upon the priority of energy efficiency and redundancy.
Some new techniques use ‘pressure control with flow feedback’. In any compressed air system, if the system storage volume is known, the rating of the loaded compressors summed, and the pressure change over time monitored, the resulting system flow can be calculated (without measuring with a flowmeter). Accordingly, decision is made to use right capacity of Compressor.
No control algorithm will tune itself, no matter how sophisticated it is. One needs to test the installed system at peak and minimum loads, and in transitions between them, both slowly and quickly. Preferably with fine-sample data-logging occurring, so data can be reviewed and specific tuning parameters changed.
Generally, Master Controllers also have remote monitoring system to keep real-time track of system performance and cost information. Managers can monitor various system KPIs (Key Performance Index) such as kW/m3/hr. Remote display and monitoring can be done using various communication protocols / methos.
Master controllers may also include controlling of auxiliary equipment like pumps, fans, dryers etc…
