Carlson Craft’s Specialty Products division in North Mankato produces rubber stamps, carbonless forms and plastic badges. The printing facility uses compressed air to clear production debris and to operate mechanical arms and levers.

In 1996, about a year after Specialty Products moved into its 55,000-square-foot space, it installed a 50-horsepower (hp) rotary-screw compressor paired with a direct-expansion refrigerated dryer.

When Cliff Anderson, maintenance department supervisor, recently began tracking the compressor’s loaded and unloaded hours, he discovered that it essentially ran 24 hours a day—about 80 percent of the time in its unloaded or standby mode. Anderson knew the system could be more efficient and sought help to explore and implement energy-saving improvements.

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• Reduce maintenance costs, down time and premature equipment replacement
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• Reduce air leaks as a result of staff training and maintenance information
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Challenges

Our challenge was to help Carlson Craft reduce operating costs in its Specialty Products facility through effective use of compressed air. The project had two primary goals:
• Identify where compressed air was wasted in the system
• Modify the system to meet compressed air demand more efficiently

Carlson Craft selected a participating contractor from our list to conduct a study. After
$2,000 in funding from Xcel Energy, the study cost Carlson Craft $1,000. The compressed air study identified leaks and their associated energy costs; determined the system’s baseline by measuring supply and demand; and recommended improvements with their payback terms and estimated energy savings.

Solutions

A few loose fittings and a 1/16-inch hole: That’s about all it took to keep Carlson Craft’s compressor running on standby all the time.

The study found a total of 6 cubic feet per minute of air leakage, which constituted about 3 percent of the system’s capacity and represented an annual energy loss of about $300. The total air leakage wasn’t such a big problem on its own—Anderson actually was surprised there weren’t more leaks—but it made a huge impact on the compressor.

The compressor was designed to shut off when not in use for 10-15 minutes. The tiny leaks, however, were enough to send a constant signal for more air. The compressor was never satisfied that the system had enough air reserves, so it never fully shut down.

Further monitoring of the system indicated that even when the leaks were fixed, the existing 50 horsepower compressor would be just too big for the job. The study recommended that Carlson Craft install a new 15 horsepower compressor. “That’s where we see the real energy savings,” Anderson said. The study also suggested a smaller air dryer.

Finally, the study recommended changing the compressed air system from a single-line to a dual-line configuration. Adding a second line reduced pressure drops, which helps equipment using the compressed air run more efficiently.

Benefits and Results

Carlson Craft repaired the leaks, and installed a new compressor and dryer.

The study provided Anderson with much-needed insight into how the compressed air system at Carlson Craft was running (and running). He was pleased with the outcome of the project, especially the energy savings. “The study gave us the data and proof that we were on the right track,” he said. After implementing all of the recommendations,
Carlson Craft Specialty Products saves an estimated $4,750 in annual energy costs. With $5,605 in total study and equipment rebates from Xcel Energy, the project payback term was just over two years.