Should I put Variable Speed Drives on every Application to save energy?

Despite what salespeople might tell you, the answer is No.

You will not save energy by simply putting the variable speed drive on every single Application, each Application is different and the amount of energy and therefore the payback period for the investment will vary vastly depending on the type and details of your Application.

A Drive will always deliver process improvements but it also creates noise and heat, so it has losses of around 2% for a standard VSD, the savings from the speed reduction must outweigh the VSD losses, put another way if you install a VSD and run it at 50hz it will cost you 2% more than not having a VSD installed, so if you are just looking at the energy-saving factor then serious consideration must be made on each Application.