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Inappropriate Uses of Compressed Air

Compressed air is the most expensive form of energy in an industrial plant. Many applications use compressed air when more efficient alternatives exist. Identifying and eliminating these uses can generate significant savings.

Cost of Compressed Air​

Efficiency Comparison​

Energy conversion efficiency:

Direct electricity:    █████████████████████████ 95%
Electric motor:        ████████████████████████ 90%
Compressed air:        ████████ 10-15%
                       ↑
                       Very inefficient
EnergyEfficiencyRelative Cost
Electricity95%1x
Electric motor90%1.05x
Compressed air10-15%7-10x

Cost per Application​

A typical system:

  • Cost of 1 electric HP: ~$0.06/hour
  • Cost of 1 pneumatic HP: ~$0.50/hour

Common Inappropriate Applications​

1. Open Blowing​

                    INEFFICIENT              BETTER ALTERNATIVE

                    Open tube                Safety nozzle
                         │                        │
                         ▼                        ▼
    Air ═══════>   ═══════>                ═══[▼▼▼]═══>
                    15 CFM                    5 CFM
                    + noise                   - noise
                    + danger                  OSHA compliant
MethodConsumptionCost/hour
Open 1/4" tube33 CFM$1.65
Safety nozzle11 CFM$0.55
Electric blower0 CFM$0.10

Alternatives:

  • Amplifying safety nozzles
  • Electric blowers
  • Mechanical brushes
  • Air curtains

2. Cabinet Cooling​

    Compressed air              Better alternative:
    for cooling:                Panel cooler

    ┌────────────┐               ┌────────────┐
    │   ═══>     │               │   ┌───┐    │
    │ Electrical │               │   │A/C│    │
    │  cabinet   │               │   └───┘    │
    └────────────┘               └────────────┘

    Cost: $800/month             Cost: $80/month
MethodCFMMonthly Cost
Vortex tube15-25 CFM$600-1,000
Open air10-20 CFM$400-800
Panel A/C0 CFM$50-100
Heat exchanger0 CFM$30-50

3. Vacuum Generation​

    Venturi (compressed air)     Dedicated vacuum pump

    Air inlet ══>                Motor ═══> Vacuum
         │                            ↓
    ┌────┴────┐                  Efficiency 40-60%
    │ Venturi │ ═══> Vacuum
    └─────────┘
    Efficiency 3-5%
MethodEfficiencyApplication
Venturi/ejector3-5%Only very short intermittent use
Vane pump40-50%General
Dry pump50-60%Clean
Regenerative blower60-70%Low vacuum

4. Material Transport​

    Pneumatic conveying          Alternatives:

    ┌─────┐                      • Belt conveyor
    │Powder│═══════════>         • Screw conveyor
    └─────┘                      • Bucket elevator
    Compressed air               • Mechanical vibrator

    Efficient only for:
    • Short distances
    • Materials that can't use other methods
    • Need for sealing

5. Pneumatic Tools for Continuous Use​

ToolAppropriate UseBetter Alternative
Pneumatic drillIntermittent, high powerCordless electric drill
GrinderHazardous zonesElectric grinder
ScrewdriverContinuous productionElectric screwdriver
SawLight workElectric saw

6. Agitation/Sparging​

    Air bubbles for mixing:

        ┌─────────┐
        │ Liquid  │
        │ ○ ○ ○ ○ │
        │○ ○ ○ ○ ○│ ← Bubbles
        │ ○ ○ ○ ○ │
        └────┬────┘
             │
    ═════════╧═════════ Compressed air

    Alternatives:
    • Mechanical agitators
    • Recirculation pumps
    • Static mixers
    • Low-pressure blowers

7. Diaphragm Pumps​

    Pneumatic diaphragm pump:

    Consumption: 20-50 CFM
    Efficiency: 10-15%

    Alternatives depending on application:
    • Electric diaphragm pump
    • Centrifugal pump
    • Progressive cavity pump
    • Peristaltic pump

Evaluation Process​

Step 1: Inventory​

List all compressed air uses:

UseLocationCFMHours/day
Line 1 blowingProduction1516
Panel coolingElectrical1024
Vacuum ejectorPackaging258
Powder transportMixing504

Step 2: Classification​

UseAppropriate?Viable Alternative?
Production cylindersYesNo
Shop toolsYesPartial
Cleaning blowingImprovableEfficient nozzles
Panel coolingNoPanel A/C
Continuous ejectorNoVacuum pump

Step 3: Economic Analysis​

For each inappropriate use:

Current cost=CFM×hours×days×$/CFM-h\text{Current cost} = CFM \times \text{hours} \times \text{days} \times \$/\text{CFM-h}

Example - Panel cooling:

10 CFM×24 h×300 days×$0.05/CFM-h=$3,600/year10 \text{ CFM} \times 24 \text{ h} \times 300 \text{ days} \times \$0.05/\text{CFM-h} = \$3{,}600/\text{year}

Alternative - Panel A/C:

  • Investment: $800
  • Operation: $600/year
  • Savings: $3,000/year
  • ROI: 3 months

Decision Table​

ApplicationIf using compressed airConsider
Continuous blowingAlways inappropriateElectric blower
Intermittent blowingUse efficient nozzlesAmplifying nozzles
CoolingAlmost always inappropriateA/C, heat exchangers
Continuous vacuumAlways inappropriateDedicated pump
Short intermittent vacuumAcceptable with venturiEvaluate small pump
Pneumatic conveyingEvaluate case by caseMechanical if possible
ToolsAppropriate for intermittentElectric for continuous

Typical Savings​

ChangeTypical Annual Savings
Eliminate open blowing$500-5,000 per point
Change cabinet cooling$2,000-10,000 per cabinet
Vacuum pump vs ejector$5,000-20,000 per system
Efficient nozzles50-70% of blowing consumption
Golden Rule

If an application uses compressed air continuously (more than 30% of time), there's probably a more efficient alternative. Investigate before accepting the status quo.