Energy-Efficient Opportunities & Solutions in Compressed Air Systems

Many companies use compressed air as a multipurpose resource in their manufacturing plan, but the use of this resource comes at a high cost to the consumer. Did you know that only 10% of the electric power consumed by an air compresses is used to raise the pressure? This article investigates and explains ways for you to save money by taking simple measures to make your compressed air system much more efficient.

Compressed Air Energy Saving Improvements

• The Big Three
  1. Reduce Air Pressure
  2. Repair Leaks
  3. Recover Compressor Waste Heat
• Others
  4. Reduce use of pneumatic tools
  5. Reduce/eliminate inappropriate uses

 

1. Reduce Air Pressue – No Cost

1. Reduce the system air pressure to the lowest possible level
2. Rule of thumb: for every 2 psi reduction, 1% of compressor input power is saved
3. Example of Savings: 150hp compressor is reduced from 110 psig to 100 psig
   Energy Savings: kWh=56,210, $=2,668; Demand Savings: 9.2 kWh, $=451;Total Savings = $3,118/yr

2. Repair Leaks – Low Cost

1. Plants with no air system maintenance program may have 20+%
2. Goal is <10% leaks (energystar.gov)
3. Relatively inexpensive to repair
4. Multiple ways to detect leaks:
   •  Ultrasonic Leak Detector (best and most accurate way)
   •  Listen for them when production is shut down
   • Apply soapy water to lines and watch for bubbling.
5. Once found, repairing leaks can be simple as tightening a loose connection.
6. Example of Savings: 2 x 250 hp compressors, 8,400 hrs/yr, average flow 500 acfm, $54,200/year, if leaks reduced from 20% to 10%.
   1. Energy Savings: kWh=61,196, $=3,978; Demand Savings: kW=63.4; Total Savings = $3,978/yr.

3. Recover Waste Heat – Quick ROI

1. Only 10% to 20% of electric power of an air compressor is used to raise pressure.
2. The remainder of that electric power is dissipated in the form of heat.
3. Up to 50% of this heat can be captured and put good use, examples below:
   • Comfort heating
   • Hot water heating
   • Feedwater pre-heating
4. Example of Savings: 125 hp compressor, 4000 heating hrs/yr, $8.00/MMBtu (gas used for heating)
   1.  Estimate 60% input power to space heat
   2.  Avoided cost for heating = $7,600/yr

4. Reduced Use of Pneumatic Tools – Low Cost

1. Because only 10%-20% of electric power is used to raise pressure, air powered tools are highly inefficient.
2. Example of Savings: 150 hp compressor, 6,350 hrs/yr operation, $0.075/kWh
   1. Compressed air cost $.28 per 1000cf
   2. 1.35 hp uses 55 cfm air (Cost to operate 1 hr = $0.92)
   3. 1.35 hp electric grinder (Cost to operate 1 hour = $0.089)
3. That’s a 93% savings!

5. Reduce Inappropriate Uses

Because compressed air is expensive, its use should be limited for applications for which no alternative is reasonable.

• Commonly Used Application	Alternatives
  Open Blowing	Broom, brush, blower/fan
  Vacuum Generation	Dedicated vacuum pump
  Personnel Cooling	Fractional horsepower fan
  Cabinet Cooling (Vortex tubes)	Mechanical cooling

Summary

• To reduce operational cost related to compressed air:
  • Reduce operating pressure
  • Repair Leaks
  • Recover waste heat
• Other improvements
  • Reduce use of pneumatic tools
  • Eliminate inappropriate uses

References:

1. No/Low Cost Energy Saving Opportunities in Compressed Air Systems; By, Keith A. Woodbury, Director, Alabama Industrial Assessment Center.
2. Motors and Industrial Systems: Optimizing Compressed Air Systems; Energystar.gov.