What do you mean compressed air isn't free? We use it every day!

Compressed air is a costly utility that is often taken for granted.

By Doug Waetjen, UE Systems, Inc.

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It is amazing that while there is so much discussion about energy and carbon reduction, most plant personnel fail to realize that there are incredible opportunities for cutting energy waste and carbon gases right under their proverbial noses. These are opportunities that could dramatically improve their companies' competitiveness.

In fact, many management personnel fail to realize that it isn’t always necessary to commit to major capital-intensive programs that produce long-term return on investments. They often are either not aware of, or just overlook, inexpensive projects with short-term, almost immediate returns that will improve energy efficiencies in their plants.

One answer is looking for and repairing leaks in utilities, such as compressed air and steam. These programs often provide a very fast and dramatic return on investment. In some cases, this has translated to hundreds of thousands and as high as millions of dollars per year without major capital investment.

Compressed air is one utility that offers tremendous savings potential. The problem is that there are many plant personnel who don’t quite understand that compressed air isn’t free. There is the attitude that since it’s just air and it’s used every day, it’s free and doesn’t require much attention, even if there are obvious leaks Unfortunately, this is far from the truth. Compressed air is an extremely expensive utility.

In fact, back in 1995, the U.S. Department of Energy instituted a Compressed Air Challenge to help industry reduce the use of compressed air by 10% by 2010. They stated that compressed air was one of the most costly utilities in plants and, of all the compressed air produced in the United States, 30% was lost to leaks. They estimated the annual cost to be around $3.2 billion.

Why is compressed air so costly? It is extremely expensive to produce, and it is very inefficient to use. Of the energy required to produce compressed air, less than 20% of input energy is left for use. That means 80% of what is paid for is used up before compressed air is put in the distribution system. Here’s an example of how inefficient compressed air is. If we compare the cost of running a one-horsepower electric motor to a one-horsepower compressed air motor, the former might cost $200 per year, while the latter $1500 per year.

One simple approach for those facilities that use compressed air is to schedule routine compressed air audits and leak surveys. Compressed air leak surveys often disclose the cost of wasted air impacting the electric bill ranging form tens of thousands to hundreds of thousands of annualized dollars.

The chart below is an example of how costly compressed air leaks can be. While the numbers relate to one leak, imagine the cost of hundreds of leaks with sizes ranging from 1/16 up to3/4 of an inch.

Air Leak Cost
Leak DIA

Air-Loss CFM/Day

CFM Loss/Day Loss/Day Loss/Year
1/64 .45 576 $0.13 $48.00
1/32 1.60 2,304 $0.51 $186.00
3/64 3.66 5,270 $1.16 $424.00
1/16 6.45 9,288 $2.04 $744.00
3/32 14.50 20,880 $4.59 $1,674.00
1/8 25.80 37,152 $8.17 $2,981.00
3/16 58.30 83,952 $18.47 $6,738.00
1/4 103.00 148,320 $32.63 $11,904.00
5/16 162.00 233,280 $51.32 $18,721.00
3/8 234.00 336,960 $74.13 $27,036.00
NOTE: Based on 100 PSI, $0.22/MCF, 8,760 hours/year.

While design and compressor efficiency are important factors to consider regarding system efficiencies, there are two other contributing factors to excessive energy consumption in a compressed air system: leaks and misuse. 

On the plant level, there are many workers who are under the assumption that “air is free,” and for this reason, air is often misused and wasted. Air leaks are ignored. It is not uncommon to walk through a plant where the tell-tale loud hissing sounds associated with gross leaks are heard and taken for granted as background noise. If leaks are too loud to be tolerated, rags or duct tape is often wrapped around them to reduce the sound level and make it more acoustically comfortable for the personnel in the area. Abuses have also been observed At times, personnel have placed air hoses in a position to continually cool their working space. In one instance, an enclosed metal box was set up in a plant with an air hose run through the top, positioned to continually blow air on soda pop cans to keep them cool.

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