The result of your "free" air energy audit will be a quotation for a brand new variable speed drive air compressor! If you really want to save energy, take the demand off the system which will switch compressors off. This will really cut your energy bills, servicing costs and reduce your carbon emissions.
However, to do this will take an experienced engineer time to investigate your system in order to work out exactly what's required to do it. The costs of our survey and any remedial works will be a drop in the ocean compared to the cost of installing and operating an air compressor.
Measuring motor power consumption gives you a guide. However if you also measure air flow, pressure and temperature into the system you can work out exactly how efficient your compressors are.
For example, we recently measured a 186kw compressor and the power consumption never fell below 132kw. A compressor company would assume that the flow rate was 800 cfm. However we recorded the flow at only 200cfm. Working off power consumption, the compressor selection would have been completely wrong.
Considering the compressors first is like the Captain of a sinking ship wanting to install efficient high speed pumps rather than fixing the hole in the bottom of the boat. If you fixed the distribution system after the compressors you'd probably find that the compressors were too big and they would then operate inefficiently.
A relatively small amount of money invested in the distribution system can save a significant amount of energy. Return on investment is generally months rather than years. See DETR good practice guides.