Plant engineers do not purchase air compressors or compressed air dryers on a regular basis. There may be decades between purchases, and with today’s more reliable and durable compressed air equipment, the interval between purchasing decisions grows ever longer. This lack of purchasing frequency, coupled with the significant investment in productivity that compressors and dryers represent, means it is important to make the right decision.
Compressed air system equipment manufacturers offer a wide variety of equipment and features to meet every need. Purchasers must weigh the costs and benefits of different options while evaluating the many variables that must be considered when purchasing a compressor or dryer. The following list starts to scratch the surface: current system layout (if there is one), end use requirements, control strategies, future expansion plans, available resources (power, water, financial, infrastructure, etc.), site conditions, intermittent end uses, available storage, etc.
The Compressed Air & Gas Institute (CAGI) is an association of manufacturers of compressed air system equipment: compressors, blowers, air drying and filtration, and pneumatic tools. Links to member websites are provided on the CAGI site. The members’ representatives are readily available to assist users in recommending the proper equipment to meet your compressed air needs. CAGI’s mission is to be the united voice of the compressed air industry, serving as the unbiased authority on technical, educational, promotional, and other matters that affect the compressed air and gas industry.
Currently, the Performance Verification Program covers lubricated rotary compressors from 5 to 200 horsepower and dryers from 200 to 1000 SCFM, CAGI has expanded the scope of the program since its inception, and future expansion is expected.
The CAGI Performance Verification Program for Rotary Compressors and Refrigerated Air Dryers is based on ISO standards and CAGI Datasheets. For further information about the standards, the datasheets, and the program, visit the CAGI website: http://www.cagi.org/performance-verification/. In addition to the Performance Verification Program, there are additional resources, including e-learning coursework on the SmartSite, selection guides and data sheets, videos and CDs, and the Compressed Air & Gas Handbook available through CAGI.
The Performance Verification Program
The Compressed Air & Gas Institute (CAGI) has developed a Performance Verification Program for rotary compressors and refrigerated air dryers to help purchasers address one key decision: which equipment will provide the compressed air needed to meet demand in the most efficient way. CAGI and its members have devoted great effort to establish the Performance Verification Program. Development of well accepted international standards for measuring performance, ISO 1217 for compressors and ISO 7183 for dryers, and adoption of a common, standardized means of reporting performance, the CAGI datasheets, took many years of hard work.
Performance standards and standardized datasheets are critical decision making tools. They offer key points of comparison for purchasers, but is the data reliable? The manufacturers provide the performance data. Can purchasers trust the data?
To ease possible concerns about the reliability of stated performance data, CAGI members that manufacture rotary compressors and refrigerated air dryers took an additional step. They contracted with an independent third party to verify their stated performance data.
The third party administrator of the program is Intertek Testing Services, a respected 127 year-old testing company. Intertek first determines a participating manufacturer's stated performance by obtaining datasheets on the participant's public website. Intertek then selects a sample for testing, ships it to the Intertek lab, and tests the equipment to the relevant standard test procedure. The outcome of the Intertek test is compared to the participant's stated performance claims, and the results are published in a directory on the CAGI website.
Participation in the CAGI Performance Verification Program is voluntary, and not easy. Aside from the time and money expended to develop the program, the participating manufacturers devote additional time and financial resources to meet ongoing program demands. Participating companies see a value in providing unbiased, third party confirmation of their performance claims. They see a benefit to reassuring potential customers that they will receive the performance that was promised. Participating companies are confident that they have conducted the necessary design and testing to ensure their stated performance is accurate.
Only participants in the CAGI Performance Verification Program are permitted to use the CAGI datasheets. So how can the datasheets and the verified data they contain help? As we stated previously, many factors must be considered when selecting compressed air system equipment, and the totality of proper selection of compressed air system equipment is beyond the scope of this article; however, the program and datasheets do address one facet of the selection process: determination of power consumption per unit volume of air and the relative efficiencies of different models.
First, match the requirements of your system with the basic information on the datasheets. Refer to the sample datasheets that appear nearby. For compressors, be sure the flow and pressure provided by the models being evaluated match the flow and pressure requirements of your system. To compare compressors rated at different pressures, corrections have to be made, typically around 1% increase in power for every 2% increase in pressure (psi). For more specific data, contact the manufacturer for a datasheet at the pressure you are evaluating if such a sheet is not available online. Similarly for dryers, be sure the flow and pressure dew point of the models being evaluated meet your system requirements.
From the available universe of models that meet basic requirements, the next step is straightforward. All other things being equal, the compressor that has the lowest specific package input power is more efficient and is the better choice. For dryers, again with all other things being equal, the model with the lowest pressure drop and the lowest specific package power is the most efficient and is the better choice.
While this sounds simple, the key phrase, "all other things being equal", must be considered. In actuality, all other things will rarely be equal. Durability, reputation, service, other features, etc., will probably vary widely. There will likely be tradeoffs and compromises, but this is normal when purchasing anything, from a camera to an automobile. The datasheets and performance verification program do not provide all of the answers to selection questions. They were designed to assist in providing reliable information about one key piece of the selection process.
Partial View of the Fixed-Speed Rotary Air Compressor CAGI Datasheet
Using the CAGI Datasheets
The information on the datasheets will also help users understand how much it will cost to operate their equipment. Use the following formula to determine the amount of electricity required to operate your equipment:
Electricity (kWh) = (Flow (cfm) X specific package power (from CAGI datasheet) x hours of operation)/100.
The result can be multiplied by the cost of electricity in your area to arrive at a good estimate of the cost of operation over a given period.
For example, a fixed speed compressor providing 500 scfm with a specific package power of 18.9 as stated on a CAGI datasheet and operated for 60 hours a week will require
(500 X 18.9 X 60) / 100 = 5,670 kWh for one week of operation. With a \$.06 per kWh cost of electricity, cost of operation is \$340.20 per week. For ease of calculation, if the compressor is operated for 52 weeks at the same level, annual cost of operation would be \$340.20 X 52 = \$17,690.40.
Partial View of the Refrigerated Compressed Air Dryer CAGI Datasheet
CAGI members recognize the importance of making the right decision when purchasing compressed air system equipment. The institute has made it easier for purchasers to make energy efficiency comparisons by developing standards and datasheets. Participants in the CAGI Performance Verification Program have gone further by having performance claims independently verified. Given the choice between purchasing equipment from a participant in the CAGI program or a non-participant, why choose the non-participant? Support those manufacturers of compressed air equipment that care enough about the industry and the users of compressed air equipment to belong to CAGI and to participate in the CAGI Performance Verification Program.
For more information, visit www.cagi.org
For more Standards articles, visit www.airbestpractices.com/standards/iso-cagi