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Energy Savers On Submersible Pumps?


jraef

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I just got wind of the fact that one of our favorite "energy saver" companies is pursuing a Medium Voltage power assembly for the purpose of marrying their "energy saver" controller to it. The intended market is supposedly submersible deep well pumps. I don't want to get into the specific problems of doing this in MV (I already know them and don't want to help them by discussing them here), but the curious thing I heard in this scenario is that they seem to think that they can save energy on submersibles! Apparently they have "proof" of the concept with their low voltage products.

 

Can anyone think of how a submersible pump could be wasting energy? The way I see it, it is either running or not. There is no "unloaded" condition on a submersible because if that were the case, the water would not be getting lifted up the hole. The only possibility is that the pump manufacturers routinely oversize the motors for the task, which I seriously doubt. Am I all wet with this thinking (pun intended), or is this just another example of their bending the truth to fit their marketing goals of attracting new investors (which is how I heard of it)?

"He's not dead, he's just pinin' for the fjords!"
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Yes, sorry. I shouldn't have been so vague, but I didn't want to name the company. It's one of those who primarily market their version of the Nola energy saver on a low voltage soft starter, but for who the soft starter aspect is secondary in their marketing efforts. I just can't see how it would work to save energy on a submersible pump.
"He's not dead, he's just pinin' for the fjords!"
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Jeff,

 

Submersible pumps are typically centrifugal pumps; not unlike those that operate above the surface of the liquid. Other than packaging, I see little difference and for sure, whether above or below the line, they all follow the same Laws of Physics.

 

So if you discount the 'Marketing Speak' .... for application of their product on centrifugal pumps operating above the surface; logic would seem to dictate that you would also have to discount their 'Marketing Speak' when their product is applied to submerged centrifugal pumps.

 

Ya think ?

 

:blink:

 

Caveat Emptor !

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If you look at the possible out come; Reduced Voltage= Reduced Torque= Reduced Speed= Reduced Flow= Reduced Energy. It is very hard to put a tacho on a deep well submersible pump so unless the application has good flow measuring equipment it shpould not be too hard to produce "Energy Saving" on a centrifugal pump without having to answer hard questions. Whenever I hear of this type of device applied to any centrifugal load i get very suspicious and wonder if anyone is checking the speed and or flow before and after the installation. ;)

Ken

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

 

It is not uncommon for submersible pumps to be connected to their power source through l-o-n-g lengths of wire .... which, , due to IR drop, cause the motors to operate at reduced voltage.

 

For fixed speed pumps, some mechanical means is required to adjust the flow or pressure. As a consequence, there is a real energy loss across such devices ....

 

Something that the purveyors of Marketing Speak seem to neglect mentioning.

 

:o

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For fixed speed pumps, some mechanical means is required to adjust the flow or pressure. As a consequence, there is a real energy loss across such devices ....

 

:o

 

Exactly, find where the real losses are and address that, trimmed impeller, pulley change, VSD etc. There are many PROVEN methods of combining flow/pressure control with energy savings.

My point was that it is very easy to show an energy saving on a centrifugal load if one of the side effects of your device is that the motor speed is reduced. If we are to measure the overall energy efficiency of a paticular pump/fan installation(or in fact any device) we need to measure the work that is being done by the equipment.

The several times that I have seen the Nola type devices demonstrated there was no attempt to evaluate the actual output of the driven load before or after installation.

 

Ken

An expert is one who knows more and more about less and less until he knows absolutely everything about nothing
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Yes, that is sort of what I was getting after. The only way to save energy in a centrifugal pump system involves lower flow. If they are restricting flow at the point of use (in this case the top of the well somewhere), then it could be argued that a VFD would be in order; but a Nola unit? The basic Nola circuit monitors power factor to determine when the motor no longer needs full torque output. It can be thought of as a PID control loop, but without the feed forward capabilities of taking in signals from the outside. So when pushing a fluid, how would the Nola circuit detect a lower flow requirement? It has no pressure feedback mechanism to "force" it into operation. If you had a PID controlled valve at the point of use somewhere, and it determined that flow was no longer necessary so it choked off the valve, when flow reduced the motor load would be lower. But the closed loop control of the Nola circuit would then start interacting with the PID loop of the valve control and the system would again become unstable, perhaps wildly so.

 

I have, on ONE occasion, seen a valid use of the Nola circuit on centrifugal pumps, but the scenario was somewhat unique (as most valid uses are for that technology). The Alaska Area Native American Health Administration had service trucks which traveled from village to village in the tundra, taking care of drinking water well jet pumps. The pumps ranged from 5HP to 15HP, and because all of their power was derived from relatively small diesel generators, they used soft starters on them to prevent voltage drop. Because of the extreme distances, the agency wanted to have the service trucks carry only one pump motor to be able to repair any unit in the field. So when they only needed a 5HP pump, they still used a 15HP motor. In that case, using Nola controllers as the motor starters for those pumps did provide them with energy savings. I seriously doubt though that most deep well submersible pumps use motors that are significantly oversized for the application. Unless there is something about that industry that I am unaware of.

"He's not dead, he's just pinin' for the fjords!"
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Just to throw in my two cents worth, submersible pumps are over fluxed by design, relying on "water cooling" to remove the extra iron losses. As such, they have a higher iron loss than standard motors and if they could be operated at reduced voltage, would probably be candidates for energy savings at higher loads than standard motors.

I have not made any tests, but I suspect that if you had a submersible pump oiperating at say half flow, then a reduction of say 10 - 20% in voltage could reduce the iron loss noticably.

This does not alter the fact that the major losses at half flow are "mechanical" rather than electrical and much higher savings can be achieved by slowing the pump down.

Best regards

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Perhaps, the motor operates in the saturation region, so that it has a VERY STIFF characteristic.

 

Because of the THRUST factor, they can have a bit of a problem starting ....

 

Making the motor stiffer, allows it to overcome the mechanical burden on starting without having to oversize the motor for the application ....

 

..... or did I miss it by a country mile, MarkE. ????

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The very long and thin contsruction of the motor makes it difficult to put a high number of turns in without restricting the iron cross section.

All design is compromise, and in this case, a higher iron loss is not an issue due to the liquid cooling, this is why the submersibles have a much higher magnetising current (and run current) than comparible air cooled motors.

 

To reduce the iron losses, the motor would need to be much larger and of course that is more dificult for a submersible!!

Best regards,

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