When you want to buy a compressor, you will define the flow and the pressure you require for your factory. Then you will check the compressor manufacturer catalogue on which model you will need. Then you compare the kW/HP size of the different manufacturers.
What they don't tell you is that : the electrical induction motors used to drive the compressor cores in a unit has a service factor.
There is so much discussions and attemps on increasing the efficiency of the electrical motors driving the compressors. Class IV is becoming the next standard for electrical motors, having a marginal better efficiency than Class III. IE Class 4 is defined as Super premium efficient.
The losses vs IE3 would reduce with 14%. Lets take a motor with 96% efficiency. 14% reduction on 4% provides a gain of 0,56% moon the total power. Always good to save energy to reduce Carbon footprint !
Some compressor manufacturers are promoting that they use Class IV electrical motors.
What nobody talks about is the Service Factor of the electrical motor.
Why is a service factor on an electrical motor needed ? The service factor is the increase of available power versus the nominal power. If a motor of 200kW has a service factor of SF=1,15 it means that the real power is 230kW.
Service factors in the compressor industry varies from 0% up to 25% !
To obtain 230kW in a frame of a nominal power of 200kW, the motor manufacturer needs to modify the motor to obtain the same lifetime. The modifications make the motor more expensive.
What can be done with a more expensive motor with a higher real power than nominal ? The motor drives the compressor at a higher power level. This is done through a gearbox, to obtain the right torque and speed at the compressor blocs.
What does a buyer of compressor looks at ? He will read the nominal power and the flow at a required pressure of the compressor ! What the real consumption of the compressor is, the user will not know until he looks at his machine he has bougth and looks on the dataplate of the electrical motor mounted.
Did you check the SF on your installed compressors ?