electrical saving

A VSD can invoke savings in power, though savings in money depend upon the Tariff and a number of other factors. VSDs can be programmed to turn the wick down a bit when the equipment isn't doing much work.

The shaft power required by any fluid mover, excluding its own internal losses, is the product of the pressure rise times the volumetric flowrate, expressed in compatible units. An item like an air compressor has a variable load that depends upon compressed air demand, and in the case of some Tariffs, cannot be "seen" within a range of other loads that may be significant.

Is the Tariff a 'kWh consumed' basis? Is it a 'peak demand' Tariff? Is the user charged for under-unity power factors? It's a bit difficult to see from here at the moment.

Depends on the air system it's supplying. If the air demand doesn't change the compressor will run longer (or run loaded longer, depending on the controls) so the energy saved likely to be small.

Cheers.....Codey

Optimally You would want a VSD that would generate a frequency output depending on air demand. That way the compressor is only producing what air is needed to hold constant air system pressure. With the ability to hold a constant system pressure them you can adjust it to the highest pressure needed thru out the system. This way the pressure is not fluctuating from a high to a low. This means you can usually reduce the pressure saving electricity.

You can fix the VFD for trial purpose and can calculate actual KWH consumption at various loads.

None - if the compressor is running slower it will run longer to fill the tank.

Travis

Running a motor at a lower frequency than it is designed for but at the original voltage may result in the magnetic elements approaching saturation where there will be high current spikes that will increase rather than reduce average current. If it is a capacitor motor (which is likely the case), there will be less current flowing through the capacitor (due to the lower frequency) and the artificial phase split induced by the capacitor may change phase angle and cause poor running characteristics. You do not say what type of motor you are using, but various types have different characteristics at lower frequencies.