Minimum Period to Record Reading for VFD

If you are talking HVAC, even this won't give you an accurate picture of your savings. You would have to factor in weather for the base year energy consumption and the current years' consumption.

Now, if you are talking a fan that runs under a steady load for continuous ventilation, boiler fan, etc, you could calculate the power based on you meter readings with and without the VSD. Take the difference and multiply times the annual run hours and you have annual energy savings.

First part I agree with. The best way to get an actual pay back is to evaluate a full years worth of run time. You could take the annual power costs from the previous year and calculate the savings in an ROI form for a payback basis but the best way is to compare both annual utility costs.

As far as the system over sized, not true. Many systems until the late 90's were designed as VAV (variable air volume) systems that would run full speed on the fans until the different zones in the buildings were satisfied. Upon satisfaction the air dampers for that zone would close and force the air into a "By Pass" and dump into a return air plenum or shaft which would then be removed from the building Via a relief fan.

Today when the dampers close the by passes have be closed (so you do not waste conditioned air) which allows the static pressure in the duct to build. That higher pressure is then sent to the VFD (VSD) via a transducer to tell the motor to slow down since you now have enough static pressure in the duct work to run the system.

Same is used in water heating systems today, the slower you can move the water through the fan coils or floor the more heat the piping can give up to the space. A 3-way or bypass valve should be used in reheat or heat systems so that once the zones become satisfied the bypass valve (3-way) opens and sends the not needed hot water back to the boiler or source raising the temperature in the supply vessel allowing it to turn off an not waste any more therms.

So they were not over designed they were designed for the times.

Hi I am not sure about the question that you are asking, please correct me if I am wrong. You had a 3 phase motor connected via Dol, then you connected a VSD to the same fan, am I correct so far?

When you also measure the current through a VSD things change, but I don't know about you Fluke Power Analyzer.

The problem is, that i can see is that you are measuring the line amps and line voltage to the VSD this does not have a linear reference to the power consumed by the VSD, this is because of the way the VSD operates in prince-able.

VS-D's are a bit like switch-mode power supplies they create harmonic frequency's, which can be bad for the power supply. This is an area that I am not so familiar with, but have accepted, this is not my strength!

VS-D's Have used what we call an energy saving mode, but with a fan, and not completely understanding your application, I don't know if this could be applied.

The thing about it is You have a fan, but you want to reduce the energy that this fan uses, why not put some power factor correction on the fan motor, because the fan will will only draw the current required to move the air required.

There would be little or no saving by installing a VSD to operate at a constant speed, but if you want to vary the speed, go for it mate.

Best Regard's

Joe

"...prince-able"

= principle.

Just being a word nazi, sorry.

Spelling is not one of my strenghts either

Cheers

Joe