Compressed air industry takes its equipment to the lab: independant laboratory to test performance

July 10, 2006
The compressed air industry is taking a step that will clear the air about the performance of its equipment. For the first time, many compressed air equipment manufacturers will submit their 50 hp to 200 hp lubricated rotary-screw compressors and 200 cfm to 1,000 cfm refrigerated air dryers to an independent laboratory for performance testing.

The compressed air industry is taking a step that will clear the air about the performance of its equipment. For the first time, many compressed air equipment manufacturers will submit their 50 hp to 200 hp lubricated rotary-screw compressors and 200 cfm to 1,000 cfm refrigerated air dryers to an independent laboratory for performance testing.The Compressor Distributors Association (CDA) led the charge that moved the industry to this decision. The CDA, a group of industrial air compressor distributors representing different manufacturers, was formed to sponsor the Compressed Air Challenge (CAC) and to have a voice in its operations. The CDA is represented on both the CAC Board of Directors and its Product Development Committee.

After several meetings, the CDA began a series of discussions about how the organization might improve the industry. The group agreed that a need existed for accurate and independently verified performance data on the equipment they provide to end users. The motivation is that distributors are being pressured to provide much more accurate system analysis and recommendations than have been required in the past.

With the ability to be accurate comes an increasing need for accurate and dependable input information. The commitment to this need prompted CDA to fund an independent, blind testing program for seven manufacturers’ 50-hp lubricated rotary-screw compressors against their published performance information. Finding a capable, well-equipped laboratory was a formidable task, as was securing the use of seven competitive machines for the short time window available.

Test results are presented as percentage variance from the published data. With test data in hand, CDA approached the Compressed Air Challenge Board and the Compressed Air and Gas Institute (CAGI)  to illustrate the need for universal testing. While there had been many discussions within the industry about independent testing, nobody seemed to be making tangible moves in that direction. CAGI members had adopted a Compressor Data Sheet to report performance data in accordance with ISO 1217, but many manufacturers hadn’t made this information readily available. After CDA’s presentations, these groups, along with ASSERTI, endorsed the value of outside verification of product performance.CAGI took the lead and worked with other organizations to formulate the testing program. Three years later, after a lot of cooperation and hard work, the program is now in place.

What’s being tested?

The CAGI compressor performance testing includes rated capacity (cfm) at full-load operating pressure (spi), total input power at rated capacity at full operating pressure (kW) and specific package power (kW/100 cfm). Refrigerated air dryers are tested for flow (scfm), outlet pressure dewpoint (degrees F), pressure drop (psid), total input power (kW) and specific package power (kW/100 cfm).

The lab will administer the program, contact the manufacturer and select a specific machine to be tested. Their random selection will come either directly from manufacturer inventory or from a distributor's stock. After the test, the manufacturer will be advised if the machine passed or failed.
Once a machine tests successfully, compressor and air dryer manufacturers will be entitled to use the CAGI Performance Label. CAGI manufacturers whose equipment fails the test will have an opportunity to correct the problem. If it can’t be corrected, the manufacturer isn’t entitled to use the CAGI label. The CAGI Web site will post a notice of non-performance, thus putting the manufacturer at a significant marketing disadvantage. The program also is being offered to manufacturers that aren’t CAGI members.

What it means to you

This testing program allows users to evaluate the data presented with new equipment bids and to feel more confident with purchasing decisions. In the most basic comparisons of machines, end users ask:

  • How much compressed air will this machine provide compared to its capital cost?
  • How much energy will it consume per unit of compressed air (cfm/bhp)?
  • How much will it cost to operate?

Answering these and similar questions always has been a fundamental step in the decision to purchase a compressor or dryer. In the past, end users could only rely on answers based solely on the information the manufacturer provided. This typically included only the full-load volume (cfm), horsepower required at full load and horsepower at an unloaded state. In sales presentations, this information most often is coupled with discussion of the control system in an attempt to evaluate the machine’s efficiency while operating at partial load, often leaving room for substantial doubt. Soon, most of these performance claims will be substantiated and reported on the CAGI Web site.

After purchase, a machine’s full-load and partial-load efficiency has been difficult to verify and often faded to a point of little interest. The result has been many, if not most, systems are unmonitored and operating with unnecessary energy consumption. Further, system changes with air users being added or removed, pressure increased or reduced, production hours increasing or decreasing, and evolving leaks can make dramatic changes in the energy consumed. Without a reliable baseline for comparison, it’s been difficult to quantify the effects of these changes.

A system analyst now can easily evaluate a machine’s performance with modern data collection tools, but reliable equipment performance information is still essential. With good data, knowledgeable compressed air system analysts can verify system performance and easily determine if the system is operating efficiently. This information also can determine if any system changes would result in substantial energy savings.

An example

Consider a plant that’s operating two 125-hp fixed-speed single-stage rotary air compressors and one 200-hp fixed-speed single-stage rotary screw air compressor. This plant operates 24 hours per day with a load that varies greatly throughout the day. The machines operate off individual controls that sense discharge pressure. Plant maintenance personnel decide when to run the 200-hp as the lead machine instead of a smaller unit.

The air system energy analysis found that during most of the day one 125-hp unit provides more than enough air to maintain pressure. For a few hours each day, the system required either both 125-hp units to operate partially loaded or the 200-hp unit to run partially loaded.

Most of the time, the plant runs with two partially loaded 125-hp units, a particularly inefficient approach given that fixed-speed compressors are inherently inefficient when operated that way. The plant considered purchasing a 160-hp variable-speed single-stage rotary air compressor to improve efficiency. The unit would be able to handle the entire load for most of each day, varying its speed to maintain pressure. During the short periods when the 160-hp unit wouldn’t be capable of maintaining pressure, one of the 125-hp units would start and run fully loaded.

Because a variable-speed compressor is more efficient than a partially loaded fixed-speed machine, the 160-hp unit would serve as a trim machine after the smaller unit loads up. Once system demand drops back into the range of the 125-hp unit, the smaller fixed-speed machine will unload and the 160-hp variable speed machine takes over to satisfy system demand.

In this case, the estimated yearly system operating cost with the two 125-hp fixed-speed single-stage rotary air compressors and 200-hp fixed-speed single-stage rotary air compressor was about $68,000. Installing the 160-hp variable-speed single-stage rotary air compressor into the system could reduce power costs to an estimated $36,000 per year. Payback on the entire project was less than two years.

As with many things, these recommendations are only as good as the input information. Accurate performance data for both the existing compressors and the machine being recommended are critical if the outcome is to be as anticipated. Before suggesting any changes, the analyst must have confidence in information being used for the decision. This same information continues to be helpful for verifying savings and in monitoring the effects of future changes in the system.

The CDA members are proud to have been the impetus for industry taking this step forward and continue to look for opportunities to promote and improve our industry. For further information, contact CAGI at

Ken Byrd is on the board of directors of the Compressed Air Challenge, the Compressor Distributor Association as well as the North American Association of Compressor Distributors. Contact him at [email protected] and (630) 766-7900.

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