Determine energy savings using VFD on constant torque load

If the application is a constant torque load with a fixed speed then the energy saving is not big and it is even possible that you will use more energy due to the lost in the variable frequency drive itself. Instead you can get much more energy saving by looking at the gear motor and choosing a gear with a higher efficacy. Around 70% of the potential energy saving is found in choosing the right drive train, motor, gear, and belt. etc.

If the application instead is running on a variable speed and with a changing load then there is also energy to be saved by using a variable frequency drive. There is a lot of literature on this subject. The most saving is due to the variable speed. This is common knowledge and has not anything to do with the Brand or model, but purely that the V/F control is used to control the speed of the motor. Even more saving can be found in application where you can use the V/F2 control, mostly in pump and fan applications. There is additional saving to be found when choosing a drive with "energy saving" functions. Here I can recommend the Gozuk GK3000 VFD. It is patterned and measurement shows up to 30 % energy saving, but it is most successful in the conveyor, pump and fan type of applications where you have a variable load.