# Energy Conservation By Vfd Drive

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### #1 surajkant

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Posted 11 November 2008 - 04:16 AM

dear all
i am new to this forum and a fresh engineer. i want to know that what is the process to show that energy is really conserved by using vfd drives and how to calculate the amount of enegy being saved.

### #2 Garat

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Posted 12 November 2008 - 08:08 AM

Dear Mr Suraj,

First you run the existing system as it is for a fixed amount of time.Note down the energy consumed.

Then fix the vfd in the system, and run the system for the same amount of time and note down the energy consumed. Difference between the energy consumptions is the energy saving.

### #3 surajkant

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Posted 12 November 2008 - 08:46 AM

Dear Mr Grat
first of all i thank you for your suggestion. can you suggest me any theoritical approach towards calculation of energy saved?

### #4 Garat

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Posted 12 November 2008 - 10:35 AM

Either connect a single phase energy meter at the input of your system or Power consumption by existing system X time gives the energy consumed.

So you subtract the energy consumption of the existing system with the VFD system in %, so that will give you directly the percentage of energy saving.

Garat

### #5 surajkant

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Posted 13 November 2008 - 06:06 AM

dear Mr Garat
thanks again. i have one more doubt . how frequency is related to the energy consumed? and for better energy consumption which type of control is best? waiting for your reply

### #6 kens

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Posted 13 November 2008 - 10:27 PM

Hi there, this can be a fairly complicated subject but the basis is not so much saving energy by altering frequency, but more about improving the process efficiency by reducing motor speed. The best examples are centrifugal fans and pumps which work on a quadratic energy curve, ie the theoretical energy is cubed by the speed. Now in reality it is not as simple as that but the idea is to remove flow restrictions and instead control flow by reducing fan/pump speed. If you have a look through the Danfoss website there are some good papers on it and also a pretty good peice of software called Energy Box.

An expert is one who knows more and more about less and less until he knows absolutely everything about nothing

### #7 billstrong

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Posted 25 December 2008 - 07:56 AM

Suppose the load is the same, then under balance condition, the torque T at low speed should be the same as at high speed.
power P=T*(2*pi*f)

### #8 Angelinabv

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Posted 12 August 2010 - 02:49 AM

H
Due to the decline in costs over the past five to ten years, and the potential for significant energy conservations, variable frequency drives (VVVF Drives) can be cost effective on a very large range of applications. Variable air volume systems

Variable air volume systems should always have a variable frequency drive (vfd) installed to control volume. A variable frequency drive (frequency converter) serving a variable air volume system operating for a typical 3,000 hours per year will pay for itself in two to five years for a return on investment (ROI) of roughly 20-50 percent. Variable frequency drives (frequency inverter) on larger motors will offer a higher return on investment (ROI).

### #9 GreenDriv

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Posted 05 September 2010 - 01:22 PM

QUOTE (Garat @ Nov 12 2008, 04:08 PM) <{POST_SNAPBACK}>
Dear Mr Suraj,

First you run the existing system as it is for a fixed amount of time.Note down the energy consumed.

Then fix the vfd in the system, and run the system for the same amount of time and note down the energy consumed. Difference between the energy consumptions is the energy saving.

I think just running VFD in the system for a time. Then compare the power consumed with the rated power of ac motor. Then you can know if the energy is saved.

Of course, it depends on the exact load information. For example, if the load is under full running, there is no energy saving, even will consume more power because you have used vfd. But if the load is not under full running, you can find the obvious energy saving.

Hope it helps.
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