How much energy did you say you could save? 4

[GGOSS]

Hi folks,

We have just completed an independant & detailed evaluation of one of the leading energy saver products and would like to present our findings to you.

- At 0% motor loading, a saving of less than 18% was achieved.

- At 25% motor loading, a saving of less than 3% was achieved.

- At 50% motor loading, a saving of less than 1% was achieved.

- At 75% motor loading, there was no energy saving to speak of.

- At 100% motor loading there was no energy saving, as you would expect.

As the above-mentioned results were achieved with a very small and inherently inefficient motor, we would expect savings potential to reduce as one moves up the kW spectrum ie where motors are generally far more efficient.

Note: The above results have not been posted in an attempt to dispute any claims made by manufacturers of this type of equipment and/or information presented by others who may have conducted similar performance appraisals. They have simply been posted to highlight that the overall performance one can expect from such devices is very much subject to variables (eg. motor design, efficiency, kW rating, number of poles & shaft loading) that are outside of our (and the product manufacturers) control. Identification of suitable applications prior to purchase is therefore strongly reccommended.

Regards,
GGOSS

 

[jraef]

GGOSS,
Excellent work. The 50% value is even less than I had expected. Granted, 1% is significant on a big load over a long period of time, but one would need to operate predominantly at 50% loading or less, and who does that? Most bean counters will not tolerate the kind of payback period that those numbers would equate to.

"Venditori de oleum-vipera non vigere excordis populi"

 

[Skogsgurra]

GGOSS,

This is very interesting. But it would be even more so if you could disclose the type of "energy saving product" - we do not need to know the make - and also the load the motor is driving (fan, pump, elevator, conveyor etc).

My experience is that even a rude stator voltage control can be quite efficient (in spite of common wisdom) especially at fan load and low power levels where VFDs have a rather high intrinsic power consumption.

This theme merits a long discussion. I think that you have started a very valuable and interesting thread.

 

[DickDV]

Modern VFD's can be considered to have power losses in the area of 2% of load KW.

That's hardly a high level and remember, it's 2% of the load KW so if the drive is reducing the speed to save energy in the load, a similar proportional savings is also available in the fan losses.

 

[BigMax]

Hello GOSS,

That's good information.

I too have recently been involved in evaluating an energy saving device and have noted results near identical to yours ;-)

In addition, the other result I noted was the power factor improvement. For example;

0% Load, pf=0.24, energy saver enabled, pf=0.41, 71% improvement!

25% load, pf=0.55, energy saver enabled, pf=0.63, 15% improvement.

50% load, pf=0.71, energy saver enabled, pf=0.72, 1% improvement.

100% load, no improvement.

WOW, surely these pf improvements at low load are a good thing? (he says, tongue firmly planted in cheek.....)

Sure enough, these were displacement power factor measurements. Distortion power factor (the 'other' type of power factor, see previous posts on this forum) was not recorded but was noted......

Being an SCR based phase angle controlling energy saver (typical for such devices?), the energy savings were achieved by reducing motor terminal Voltage, by reducing SCR conduction below 360 degrees at low loads. The result? Harmonic current distortion and DECREASED distortion power factor!

Imagine a factory full of motors controlled by such energy savers, what effect would the resulting THD have on power quality? This effect has not been discussed on any energy saving device information that I have reviewed. Interesting.

These are my personal observations only, and are not necessarily those of my employer. Nor do I seek to discredit any claims by any energy saver manufacturer, 'cause I haven't seen any such claims!

Cheers!

BigMax

 

[GGOSS]

Scogsgurra, Without mentioning brand, our studies were conducted on an electronic energy saver (nola based) type product. Motor loading was controlled via an eddy current coupling arrangement.

jraef, we extrapolated the information to determine payback periods. You're comments regarding the bean counters are very valid if the product is being purchased specifically for its energy savings ability. Having said that the product we evaluated also provided a soft start and therefore the benefits achievable through the use of that feature would also need to be considered in any payback calculations.

BigMax, I am interested in the additional information you have presented as our study was limited to comparing kW consumption with the energy saver fucntion ie comparing disabled and enabled measurements. You have obviously undertaken a more detailed approach to your evaluations, 1 star for effort goes to you. Did you by chance measure THD levels?

Regards,
GGOSS

 

[OperaHouse]

"Imagine a factory full of motors controlled by such energy savers, what effect would the resulting THD have on power quality?"

And that sort of thing happens. A German company designed a photo sensor with a power supply that triggered on the phase angle. Simple design, but they forgot that many customers had 30-50 sensors on one control transformer. That createed an enormous power surge. That product was pulled from the market and the power supply was redesigned.

 

[mc5w]

If your motor's duty cycle is such that it is spending 50% of its time at no load, then you would get 9% energy savings. In this case a reduced running voltage controller could save you a lot of money.

It would be possible to implement a reduced voltage controller by doing solid state switching of an autotransformer that is rated for continuous duty rather than starting duty. That would get rid of your harmonics problem.

Copied this thread to my hard drive.

Mike cole, mc5w@earthlink.net

 

[electricuwe]

Mike (mc5W),

unfortunately I have to disagree with your statement psoted on Oct. 16th. You have to consider that no load power consumption is much smaller than full load power consumption. So saving 18% half of the time will not result in a total saving of 9 %

 

[Marke]

Yes I agree with eletricuwe

18% of what??

If this is a small machine, then the no load power consumption could be as much as 20% of the rated power of the motor. 18% of 20% is 3.6% of the motor rating.

In practice, the number of applcations where the true no load shoft load is zero are very small. Most would have a no load shoft power consumption of at least 25% and so the energy saved is even less.

If we assume a no load shaft power of 0, then 50% full load and 50% no load would yield a saving of 1%
On larger machines, the open shaft power consumption can be as low as 5% of the motor rating, so 20% of 5% is very small.

This "percentage" quoting by suppliers is most missleading as the natural interpretation is to refer that back to the motor rating when in fact it refers to the "off load" power consumption.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[mc5w]

The no load losses of a large motor can be considerable. Normally, you do not overmotor something too much. MOST 3-phase motors get optimal efficiency and life at 60% to 85% of full load. Above 85% you start to run into the motor only getting 10 years of life and below 60% the magnetizing and aerodynamic losses take over and the motor runs too cool to drive out moisture.

However, for some industrial machines such as punch presses and vibratory finishers, you have to size the motor for the largest die and for vibratory finishing with steel shot respectively. If you are using corn cob meal or light stones in a vibratory finisher then the motor loafs.

Likewise, there is such a thing as a 350 ton die that belongs in a 1,000 ton press because the die generates more than its fair share of vibration. You need the mass of the larger press to absorb the excess vibration. Not the only instance of strange and unusual.

Mike Cole

 

[Marke]

Hi mc5w

I am interested in your statement that "[red]The no load losses of a large motor can be considerable[/red]"

Can you please provide more detail on this and what levels of losses you expect on larger machines. I am interested in the magnitude of the losses relative to the motor rating.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[mc5w]

Just simply a matter that you have turning parts and cooling fans using energy AND you have hysteresis loss and eddy current loss in the steel core. A TYPICAL 3-phase motor has no load magnetizing current of about 50% of full load which means that the no load iron loss at no load is about 25% of at full load. The change in conductor loss is even higher.

Transformers are even worse at no load because the core magnetism and magnetizing current vary only a little. If a power transformer is built right then most of the secondary flux and primary flux balance off except for magnetizing reactive and iron loss current.

What I am trying to say is that if you cut the voltage in half you can make a 100 HP motor act like a 25 HP motor when the load is light.

This is also not much different from how an aversized piston engine wastes a lot of energy on keeping its parts moving AND keeping itself warm. General Motors one time tried experimenting with a V-8 engine that could shut off 2 or 4 cylinders at medium or light load respectively. Unfortunately, they introduced it into a Cadillac model year that also had some other new features that were rather buggy. If they had waited a year to get hte bugs out of the other innovations they would have had better chances. Electronic valve trains running on 36 to 42 volts DC might make the technology viable.

 

[Marke]

Hi mc5w

Interesting comments and certainly along the lines used by promoters of the energy saving systems, however, from my experience, the magnetising current for large motors is typically in the order of 20 - 25% of the rated current, and the iron/core loss is commonly in the order of 2 - 5% of the motor power rating. This is pretty small.
Small motors have a higher magnetising current and consequently a higher iron loss, but this is still less than 25% in my experience except on fractional horsepower motors.
Can you point to fact and data, perhaps web based datasheets to show this high iron loss on medium sized motors?

Best regards,


Mark Empson

http://www.lmphotonics.com