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Controls & Automation

Compressed air system control is as important as the compressors themselves. A well-controlled system can reduce energy consumption 10-30% compared to inadequate controls.

Why It's Critical​

System without optimized control:  System with optimized control:

  Compressor 1: 100%                Compressor 1: 100% (base)
  Compressor 2: 100%                Compressor 2: 75% (trim)
  Compressor 3: Modulating 40%      Compressor 3: OFF

  Power: 300 kW                     Power: 210 kW
  Efficiency: Low                   Efficiency: High
                                    Savings: 30%

Control Levels​

Control Hierarchy​

┌─────────────────────────────────────────────────────────┐
│              LEVEL 3: SUPERVISION (SCADA)               │
│         Remote monitoring, historians, reports          │
└────────────────────────┬────────────────────────────────┘
                         │
┌────────────────────────┴────────────────────────────────┐
│            LEVEL 2: MASTER CONTROL                       │
│      Sequencer, optimization, load balancing             │
└────────────────────────┬────────────────────────────────┘
                         │
┌────────────────────────┴────────────────────────────────┐
│            LEVEL 1: LOCAL CONTROL                        │
│      Control of each individual compressor               │
└─────────────────────────────────────────────────────────┘

Level 1: Local Control​

Each compressor has its own controller that manages:

FunctionDescription
Start/StopStartup and shutdown sequence
ModulationCapacity adjustment
ProtectionsTemperature, pressure, motor
AlarmsFaults and warnings
CommunicationLink to master control

Level 2: Master Control​

The master controller coordinates multiple compressors:

FunctionBenefit
SequencingOptimal start order
Load balancingEfficient distribution
RotationEven equipment use
OptimizationMinimum energy consumption
RedundancyAutomatic backup

Level 3: Supervision (SCADA)​

Supervisory control and data acquisition system:

FunctionDescription
Remote monitoringView from anywhere
HistoriansOperational data logging
TrendsBehavior analysis
ReportsKPIs, efficiency, costs
AlarmsEmail/SMS notifications

Control Philosophies​

Cascade Control (Traditional)​

Compressors start in sequence based on pressure:

Diagram of cascade control for compressed air, showing pressure bands used to sequence multiple compressors for efficiency

Advantages:

  • Simple to implement
  • Easy to understand
  • Low cost

Disadvantages:

  • Wide pressure band
  • Doesn't optimize efficiency
  • Excessive cycling possible

Target Pressure Control​

All compressors work to maintain a target pressure:

Graph showing stable system pressure with target pressure control vs. a wider, inefficient pressure band

Advantages:

  • More stable pressure
  • Higher efficiency
  • Better for VSD

Disadvantages:

  • Requires advanced controller
  • Higher initial investment

Base + Trim Control​

Compressors divided into roles:

┌─────────────────────────────────────────────────────────┐
│                    SYSTEM LOAD                           │
│                                                          │
│  ████████████████████████████████████░░░░░░░░░░░░░░░░  │
│  ▲                                  ▲                ▲  │
│  │                                  │                │  │
│  BASE                              TRIM           STANDBY│
│  (fixed)                        (variable)               │
└─────────────────────────────────────────────────────────┘

BASE: Fixed speed compressors operating at full load
TRIM: VSD compressor that adjusts the difference
STANDBY: Backup compressors
RoleCompressor TypeOperation
BaseFixed speed100% load
TrimVSDVariable per demand
StandbyAnyStandby

Communication Protocols​

Common Protocols​

ProtocolDescriptionApplication
Modbus RTUSerial RS-485Legacy equipment
Modbus TCPEthernetCurrent standard
ProfibusIndustrialAutomation
Ethernet/IPIndustrial EthernetPLC integration
BACnetBuildingsHVAC
OPC UAUnifiedIndustry 4.0

Typical Architecture​

Diagram of a SCADA hierarchy for a compressed air system, showing levels from field devices to PLCs and master controllers

Key Performance Indicators (KPIs)​

KPIFormulaTarget
Specific powerkW / 100 CFMless than 20 kW/100 CFM
Load factorLoad hours / Total hoursgreater than 85%
Pressure stabilityStd. deviationless than 0.2 bar
AvailabilityOperating time / Scheduled timegreater than 98%
System efficiencyCFM delivered / CFM producedgreater than 85%

Automation Benefits​

BenefitTypical Savings
Optimized sequencing5-15% energy
Detected leak reduction10-20% energy
Narrow pressure band1-3% per 2 PSI
Predictive maintenance20-30% maint. costs
Unplanned shutdown reduction50-70%
ROI

A master control system typically pays for itself in 1-2 years from energy savings alone. Additional benefits (maintenance, availability) are bonus.