Unplanned energy savings

Engineers at Arnold Air Force Base Arnold Engineering Development Center test jet engines in seven test cells that can simulate air pressure at altitudes up to 100,000 ft. The facility relies on compressed air for hydraulics, control valves, and maintenance tools, but the air compressors were getting old and frequently breaking down. When engineers installed new compressors, they also cut energy costs.

Some energy savings came from increased efficiency, but better control of the compressors produced the bulk of the savings. “The old system cost $794,000 a year in energy costs and $150,000 a year in maintenance costs, just to run two compressors” said Investments and Design project manager Fred Hutchinson. “The new compressors cost $345,000 for energy and $65,000 for maintenance. That’s a savings of $534,000 a year in 2009 dollars, of which $449,000 is energy savings for electricity and water for cooling.”

The old compressors operated either fully on or fully off and the ran 24 hours a day. Thus, they produced more compressed air than was often needed, particularly during maintenance days when no testing takes place. The new compressors, which produce 1200 to 1300 SCFM (standard cubic feet per minute), have variable operating modes so the don’t need to be fully n when needed.

In addition, the new compressed air system has two 20,000-gallon storage tanks. Thus, the compressors need run only when the pressure in the tanks reaches a preset level. “On a typical maintenance day, all of the old compressors ran as where now, we might need just one new compressor,” said system engineer Mike Hollis. “The demand comes out of the storage tanks,” said Hollis. “The compressors just refill the tanks.”