Comparing compressor performances across different manufacturers has long been a difficult task. For a many years, it was all too easy to present data that, although accurate, was potentially misleading. Manufacturers were selective about what information they published as well as what conditions they chose to specify performance. The result was a numbers game that the buyer frequently lost.
Fortunately, the Compressed Air and Gas Institute (CAGI), in cooperation with its members, has developed a tool for a fair comparison between compressors. CAGI is a non-profit organization of competitive companies that manufacture air and gas compressors and related equipment. CAGI seeks to educate end-users to promote effective, safe, and energy efficient uses of compressed air and gases.
Performance Verification and Data Sheets
CAGI members have worked closely with several standards development bodies such as PNEUROP (CAGI’s European counterpart) and the International Organization for Standardization (ISO) to develop key standards for compressed air and gas systems equipment.
Under the Rotary Compressor Performance Verification Program, rotary compressors are tested according to ISO 1217 (Annex C for fixed speed compressors and Annex E for variable speed compressors). There is a standard form for participating members to publish their compressor performance information and the values published on the form are then subject to third party testing and verification.
Kaeser publishes its performance data sheets on dedicated webpages, as do other participating manufacturers. In addition, CAGI publishes the links to the manufacturers’ data sheets on its website at www.cagi.org/performance-verification/data-sheets.aspx.
CAGI data sheets are a huge help in selecting the most energy efficient compressor. By standardizing the values recorded and how the measurements are taken, it is possible to make clear “apples to apples” comparisons between two or more models. The bottom line on the data sheet is the “Specific Package Input Power at Rated Capacity and Full Load Operating Pressure”. This value (expressed in kW/100 cfm) is the measure of or “shows” how efficiently a compressor package produces compressed air. The lower the value, the more efficient the package is. This is a quick and easy way to see which compressor performs better at the stated conditions.
Finally, it is important to understand that while the efficiencies of individual compressors in a system are important, the overall efficiency of a compressed air system is usually more dependent on the sizing of the compressors and how they are controlled. Using the CAGI data sheets, you will find some compressors are a few (or even several) percentage points more efficient than others of the same size. This can generate worthwhile savings and should be a strong consideration in choosing a compressor, especially in larger sizes. But don’t overlook the opportunity for even greater electrical power savings (typically 5 – 35% or more) by doing the analysis to choose the right size compressors and control them efficiently.
To download a complimentary white paper of this blog entry that includes a line-by-line explanation of both CAGI data sheets, visit www.kaeser.com/whitepapers.
Werner Rauer is the Product Manager for rotary screw compressors at Kaeser Compressors, Inc. He has a degree in Mechanical Engineering and has been with Kaeser USA for 27 years.