The U.S. Energy Department estimates that air compressors use as much as 10% of all electricity generated in the U.S., and as much as 50% of this energy is wasted. Compressed air leaks alone account for 25-30% of compressed air use. 

Consequently, many industrial companies are identifying ways to lower their compressed air system energy consumption. One of the most popular methods to do so is a comprehensive compressed air assessment, or “air demand analysis.” The objective of this paper is to define the five steps required in a compressed air assessment.  

Step 1: Conduct a site survey
It is important to list and understand all the equipment in a compressed air system before installing any measurement devices so that 1) the devices are properly placed, and 2) system dynamics are properly understood. The person responsible for collecting information should note: environmental conditions, physical layout, and system components. 

Step 2: Measure and quantify kW / 100 cfm
Power, flow, and pressure should be measured for a period of 10 days to obtain an accurate system snapshot (other data points such as pressure dew point [to determine air quality], vacuum, and temperature should be measured as needed based on system requirements). 

The measurement period should include nights, weekends, or other downtime to identify non-productive demands. True power used by the air compressors is measured using kilowatt meters which monitor amperage, voltage, and power factor. Data loggers should record data points on each air compressor every 0.5 seconds, and average the data over a preset recording interval. A finer resolution may be needed to log specific events.

A suitable Key Performance Indicator (KPI) for all compressed air systems is specific power consumed (kW) per 100 cubic feet per minute (cfm) of compressed air used in the plant. This provides an idea of how efficient a compressed air system is – regardless of varying plant output levels. Recommended systems have a KPI below 21 kW / 100 cfm.

Step 3: System dynamics
The system information collected should be thoroughly analyzed and areas of improvement should be identified. Multiple scenarios should be considered to lower the compressed air system’s energy consumption, including an analysis of the major compressed air users within the facility to determine whether compressed air is the most efficient option for each application.

Step 4: Implementation
Many system assessments focus on reducing compressed air consumption by fixing compressed air leaks or through eliminating “inappropriate uses” of compressed air. Using engineered air nozzles, for example, to replace perforated pipe for blow-off applications will reduce compressed air demand. Real energy savings, however, will ONLY be realized if the controls on the air compressors can capitalize on these gains. This includes proper use of a variable frequency drive (VFD). 

Step 5: Verify performance
Utility rebate programs sometimes require energy savings be verified by an additional compressed air assessment performed after the air system is optimized. In cases where utility rebates do not require such a degree of verification, facilities should still consider implementing some form of a post-optimization assessment. All systems can be enhanced – even systems designed using air assessment data and that are newly installed.  

Conclusion
It is critical to focus on improving the specific KPI of kW / 100 cfm. Compressed air users can ensure return on investments (based on energy savings) on air system assessments by working with firms who measure, at a minimum, power, flow, and pressure over a period long enough to obtain an accurate system snapshot, often 10 days. 

Further, the data obtained from the assessment must be thoroughly analyzed and recommendations should be made based on conservative estimates of power reduction. When implementing an optimization plan, it is important to remember that without proper system control, the system’s overall energy consumption may not be significantly lowered. 

Finally, users who complete a compressed air assessment and optimize their systems will surely reduce energy consumption and see lower operating costs. However, even the best, newly optimized systems can always be further improved. Facilities should be advised that additional savings can be determined by completing a leak detection audit in conjunction with a full evaluation of the demand side of the facility for the appropriate use of compressed air.  

Source: Neil Mehltretter is the technical director at Kaeser Compressors, Inc. For more information on Kaeser, call 877-788-1829 or visit  us.kaeser.com. Excerpted from the whitepaper “Comprehensive compressed air assessments: The 5-Step Process,” which is available by clicking here.