Generally, in the past, it was nearly impossible and confusing to compare two different air compressors with different rated discharge pressures and specific power (which is the energy consumption metric). However, this is no longer the case, CAGI has introduced an efficiency rating value on its Compressor Data Sheets – Isentropic Efficiency.
Utilizing isentropic efficiency is similar to using a Monroney window sticker when purchasing a new vehicle. For example, the Monroney sticker explains the projected miles per gallon of the vehicle, price, features, and other useful information that helps assist buyers when purchasing a new vehicle.
Isentropic efficiency incorporates operating pressure and greatly simplifies the process of comparing the efficiencies among several like-sized compressors each having slightly different full load operating pressures. For example, for the same horsepower compressors, one sheet may show 125 psi operating pressure and another may show 130 PSIG, so comparing isentropic helps equalize the comparison. This video, developed by Compressed Air Gas Institute (CAGI), explains how specific power is converted to isentropic efficiency.