Getting verified performance from compressed air dryers

CAGI testing shows standards don’t always equal performance.


An example of a compressed air dryer that has met the CAGI testing specifications. The CAGI logo can be seen on the upper right of the unit. Courtesy: CAGIRemoving water from a compressed air systems is a fundamental requirement of a well-designed compressed air system. Excess water can reduce product quality, increase maintenance costs, and reduce the productive life of equipment. End users, distributors, and specifying engineers must be certain that the actual performance of the compressed air dryers matches the expected performance, as deficient dryer performance will negatively effect financial and operational performance.

There are several ways to remove excess water from compressed air systems, however one of the most popular ways is by using a refrigerated compressed air dryer. Refrigerated dryers remove water from compressed air by cooling the compressed air, condensing the water vapor in the compressed air, and removing it from the system. (For more information about treatment and drying of compressed air, visit the Compressed Air & Gas Institute (CAGI) Website

As with most equipment, purchasers of refrigerated compressed air dryers face an initial purchase price as well as ongoing operational expenses. These expenses include the power to run the dryer and pressure drop that arises as the compressed air flows through the dryer. Reputable compressed air dryer manufacturers rate equipment to the ISO 7183 standard, Compressed Air Dryers—Specifications and Testing. The ISO 7183 standard provides a uniform means of testing dryers to determine the critical performance parameters of outlet pressure, dew point, and flow (also referred to as capacity or size), as well as the power consumption and pressure drop ratings that impact the ongoing costs of operating compressed air dryers.

Performance verification

The air drying and filtration section of CAGI recognizes the need for purchasers, specifying engineers, and users of refrigerated dryers to receive accurate performance data, including flow, power consumption, dew point, and pressure drop ratings. The section members agreed to publish ratings in accordance with ISO 7183. Many members took the additional step of developing a performance verification program where participants send performance data to be verified by a third party test lab. The CAGI Website has more information about the performance verification program, datasheets, and a list of participating companies.

Someone who purchases a dryer from a company participating in the CAGI performance verification program can be assured that the performance of the purchased unit will match expectations. But what about dryers that are produced by manufacturers that do not participate in the CAGI performance verification program? CAGI tested a unit that did not participate in the performance verification program.

The unit was purchased directly by Intertek, the same third party test lab that CAGI uses to administer its performance verification program, and the unit was shipped directly to the test lab. Intertek obtained performance claims from product brochures on the manufacturer's Website and tested the unit to the ISO 7183 standard, using the same requirements that apply to units tested in the CAGI program. Below are the official test results generated by the lab:

*Specific power input at full flow, kW/100 cfm

**Considering allowable tolerance in standard, result if manufacturer was a participant in the CAGI performance verification program.

End users that purchase this dryer model based on the claims of the manufacturer would have far more water in their system than what the manufacturer claimed. The difference in dew point is significant and could result in potential damage to the end user's equipment and facilities; i.e. pneumatic tools, piping, etc., and have a negative impact on products or manufacturing quality. The increased pressure drop through the dryer would reduce system pressure, leading users to increase compressor operating pressure to compensate, thereby increasing power consumption of the air compressor.

The performance of this 200 cfm dryer is disappointing when compared to the manufacturer's claimed performance, but imagine extrapolation of these deficiencies to larger dryers. For example, assuming similar failures in a 1000 cfm dryer, an additional 5.3 gallons of water would be introduced into the compressed air system per day. Economic losses due to additional pressure drop (above claimed performance) alone would be approximately $1,300 per year at $.07/kWh. A distributor who sold this dryer to customers would have a lot of explaining to do, as poor product, damaged production equipment and facilities, excess corrosion, and decreased profitability most likely would damage the distributor/customer relationship. Continued reliance on such dryers could lead to a distributor's reputation and expertise being questioned in the market.

The CAGI refrigerated dryer performance verification program has been operating for several years now, and manufacturers have had ample opportunity to join the program. Manufacturers are able to participate in the program whether they are members of CAGI or not.

- Rick Stasyshan is a CAGI Technical Consultant.

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