Comparison of Compressed Air Flow Measurement Techniques for Industrial Energy Efficiency Enhancement

Across the industrial sector, compressed air is utilized as an easy-to-use and readily accessible tool in a variety of applications. This tool is commonly misunderstood as being more efficient than it is in reality. Air compression is energy intensive and thus both economically and environmentally costly. Compressed air typically only achieves around ~15% efficiency if judged by the energy delivered from the air, meaning approximately 5-6 kWh are wasted for every 1 kWh of useful work performed by compressed air. Due to this energy intensity, compressed air systems have become a prime target for improvement to achieve energy consumption reduction goals. Quantification of a compressed air flow allows for more efficient utilization and distribution by recognition of wasteful usage. The measurement of this flow can be used to determine cost associated with equipment operation, create specific power trends for the compressors within the system, and determine the most economical efficiency projects. This has resulted in a number of methods for the measurement of compressed air flow both from within and without the piping. The error associated with the measurement methods determines the precision of the compressed air system efficiency, so this is paramount to achieving economic analysis of energy efficiency projects associated with compressed air systems. The flow measurement methods tested in this study reveal a higher error percent in the external measurement compared to the internal measurement methods. Of these external measurement methods, the ultrasonic method yielded the highest error. The most accurate measurement method is determined to be the thermal mass type flow meter.