VFD doesnt save power??...

[VFDTech]

NO doubt you know your stuff about pumps and affinity laws. However your knowledge in the latest VFD design lacks. You even state ABB as your target. This is humorous mostly because not only has ABB been the leader in VFD program and application design for nearly 20 years, but they are the ONLY drive manufacturer who has developed an internal PI loop based strictly on load and power consumption. They were the first to develop the Square Volts/HZ ratio... thus supplying only the voltage necessary for the load curves of a pump. NOW, its even gone farther than that with the newest ACH550, whereby they actually monitor the output, and IF the load is not excessive, it not only reduces the output voltage, but ALSO THE CURRENT... THUS Power as a whole... in the past this was thought to be actually breaking the laws of physics, NOW its simply a possibility. Therefore Mr pump, no discredit to your knowledge of centrifugal pumps, but you are the one lacking in up to date technology regarding VFDs.. put that in your pump and .... it! 

[Cary Austin]

Ahh, so I have irritated yet another VFD salesman or engineer who would like to pass off the VFD as a “perpetual motion machine”.  Sorry, the volts/herts ratio thing is not new.  But it has absolutely nothing to do with the power needed by the pump to supply the flow and head required.  No matter how you supply the power, it still has to be enough to spin the pump and deliver the flow and head needed.

You are right that I maybe lacking in some of the “latest” improvements to VFD’s.  This is because there have been so many “upgrades” I can’t keep up.  Ever since I started working with VFD’s some 25+ years ago, they have made major changes every 12 to 18 months, trying to solve some of the inherent problems.  I have tried to keep up.   But in the process I may have forgotten a lot about VFD’s.

With every “upgrade” VFD’s have gotten better at reducing stray voltage, harmonics, voltage spikes, bearing currents, and skipping critical speeds.  Yet the problems from VFD’s are caused by “laws of physics” and can never actually be solved.   With every upgrade VFD’s have gotten easier to program, smaller, lighter, and cheaper.  But no matter how many “upgrades”, they will never be able to “break the laws of physics”.  It is always going to take X amount of energy to produce Y amount of gallons at Z head in feet, no matter how you spin the pump.

The problem has always been that VFD experts want to forget that head is the most important part of pumping.  I don’t know how many VFD articles I have read that are completely incorrect.  The VFD expert will say “reducing HP by the cube of the speed means a 100 HP pump slowed by 50% will only use 12.5 HP”. 

This is completely neglecting the fact that head is reduced by the square of the speed.  Reducing the pump speed by 50%, also reduces the head or lift by 75%, which means it quit pumping a long time ago.  Typically a pumps speed can only be reduced by 10% at the most, and still produce enough head to get water out of the well or to the top of a water tower.  Reducing the speed by 10% means reducing the power required by only 27%, not by 87.5% as VFD salespersons would like for you to believe.

If you know how to read a pump curve, you can see that the power required is naturally reduced by about 50%, simply by reducing the flow rate, without changing the pump speed at all.  So a VFD is just trying to trick a pump into doing something it already does naturally, and VFD salespersons would like to keep that fact from being understood.  Going on about “internal PI loops, volts/hertz ratios, and monitoring power output is just “baffling with BS”, because there is nothing brilliant about it.  A VFD will never be a perpetual motion machine no matter how complicated you make it sound.

The vile and venom spewed by VFD proponents is reminiscent of what Columbus must have experienced when he tried to explain that the world in not flat.  But all the vile and venom that ever existed does not change the fact that the earth is actually round, and VFD’s do not save energy.

Therefore Mr VFD, no discredit to your knowledge of VFD’s, but you are the one lacking in technology regarding the natural characteristics of pumps .. put that in your VFD and .... it!

[VFDTech]

Irritated?... is this your intent?... No mr wannabe-salesman, you have done no such thing. Vile and Venom?.. Columbus?. Perpetual motion? Who said anything about perpetual motion?... You are one of those geeks who gets caught up in the hype of nonsense and wants to say HEY, listen to me!!... you don’t get laid much do you?... Aside from all that, as I said,pump curves are nothing new, head pressure is dropped significantly upon reduction of speed, but to say that a VFD does not save as opposed to across the line starting is simply ludicrous. .. hope you don’t try to get customers with your dramatized jerry springer monologue… just stick to the facts.. and looks like you don’t know them as well as you want people to think you do… easy on the over inflated wording… you are about to bust a line… And I am not a VFD salesman nor engineer.. just your average tech/teacher.. not attempting to sway by means of baffling BS… but you might want to get a life… and chill out

[Cary Austin]

Now that’s funny, but also sad!  A “teacher” should know what he/she is talking about before “teaching” it to others.  People who finally “get it” tell me they had to un-learn what their “teacher or professor” “taught” them, which is sad. 

If you really believe a VFD can save energy, then you also believe it is a perpetual motion machine, whether you said it out loud or not.  Because there is no more efficient means of pumping than to use a properly sized pump, running on across the line controls, operating at it’s best efficiency point. 

Add a VFD to that and you are increasing the energy use in several ways.  The parasitic losses or energy used by the VFD equipment itself, increases energy consumption.  The loss of motor efficiency from operating on pulsing DC voltage from a VFD compared to pure sinusoidal AC current as with ATL, increases energy consumption.  The harmonic current from a VFD increases motor heat losses, increasing energy consumption.   Harmonics fed back to the grid from a VFD increases energy consumption of every other electrical device on the entire grid.  The air conditioning required for proper cooling of the VFD, increases energy consumption.  The energy reduction for decreasing the speed of the motor is not linear to the reduction in flow, which increases the energy consumption per gallon produced.  Replacing equipment that was prematurely destroyed from all the VFD problems listed earlier increases energy consumption.

I know how to read a pump curve, so break one out if you can prove me wrong.  To say a VFD saves energy is ludicrous, to anyone who knows the facts.  I am use to these kinds of insults from people who already fell for the VFD hype, drank the Kool-Aid, and don’t have the facts to argue the point.  Since this is my forum, I could easily delete all your personal insults.  But I want others to see the kind of things people say to me for posting the truth about VFD’s.  You need pretty tough skin to say that VFD’s are a scam.  Because most everybody else in the industry, is either part of the scam, or fell for it hook, line, and sinker like Mr. VFDtech.

I locked this thread so you can’t delete anything.  You may start another if you have ANY facts to show.  I can only hope some of your students read this, realize teachers are not infallible, and start doing some research on their own.