Metering Air Compressor Systems for Efficiency: A Progress Report

Air compressors have energy efficiency quantified as SCFM/BHP. However, this efficiency fluctuates over a broad range based on the loading of the compressor. When multiple compressors operate with varying loads, as in a central plant, the overall system efficiency is totally unknown. With funding from California Energy Commission under the PIER Program, we spent considerable effort over the past few years to develop system efficiency for air compressor central plants. The system efficiency was termed CASE Index, which varies from 0 to about 320, and has the units of SCF/KWH. The procedure we developed, involved metering of input (KWH) and output (SCFM), in and out of the central plant. After the initial beta testing of the procedure, as more and more compressor professionals started to use the procedure and as more metering equipments entered the picture, some metering complications were encountered. These problems were dealt with and the procedure developed under this project can produce reliable data. This paper also presents the system efficiencies we have recorded so far and the opportunities they indicate. The data shows a wide range, from a low 82 to about 250 on a 0 to 320 scale. This confirms our expectations of large energy efficiency improvement potential in compressed air systems