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nuckolls.bob(at)aeroelect
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 Posted: Sun Dec 13, 2009 10:31 am Post subject: Power Opti-Miser |
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| Quote: | Manufactures compete to make their appliances efficient.
It is hard to economically make the appliances more efficient.
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Exactly. If it were possible for any current
manufacturer to make their product more "green"
there's certainly plenty of political and
economic pressure to do it.
| Quote: | In rural areas, long runs of parallel utility lines create a
capacitance which reduces the power factor, but in the opposite
direction as inductive loads. The utility company counteracts this
excessive capacitance by installing inductors on the electric
poles. Perhaps you have noticed what appears to be transformers on
poles and wondered why they were there with no houses around.
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I think you've got it reversed. Transmission lines
offer small inductive reactances that become significant
when the lines are very long. Hence the occasional addition
of an array of power factor correcting capacitors on
some isolated pole. One capacitor for across each of
three phases.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
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nuckolls.bob(at)aeroelect
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| Posted: Sun Dec 13, 2009 10:31 am Post subject: Power Opti-Miser |
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At 03:25 PM 12/12/2009, you wrote:
| Quote: |
Perhaps I'm dated but most capacitor start motors only used the
capacitor to get a phase change for starting. The capacitor did not
do anything for running PF correction IIRC. Have things changed?
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No . . . digging around in the gray matter seems to
dredge up some things I used to teach about induction
motors at Great Lakes. The capacitor(s) on a motor
are for starting (the BIG guy) paired with the
occasional second, smaller device for running.
My central air conditioners and shop air compressor
are fitted with a pair of Start/Run capacitors.
And you're right, those capacitors are selected for
optimized rotation of a magnetic field in the stator
when only single-phase power is available. They're in
series with one or more windings and NOT for PF correction.
P.F. correction needs to be in parallel with the main
winding.
So, depending on how high the resistive losses in
the main winding, there could be some significant
degradation of power factor. But the motor guys
are as sensitive to temperature rise due to I(squared)*R
as are the guys who transformers and other wiring.
They'll do what economically practical to minimize
said losses.
I think one of the articles that were cited over
the past few days suggested that average power
factor for a home was .90 . . . so it would be
difficult to realize much savings in I(squared)*R
R losses when the majority of said losses are
spread over ALL the building's distribution system.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
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klehman(at)albedo.net
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| Posted: Mon Dec 14, 2009 5:45 am Post subject: Power Opti-Miser |
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If a NOLA type controller was cheap enough, I think it would give a
return on investment (saved I squared * R) on some air conditioner
compressors. The load and current draw of some of these compressors
varies significantly (at least 25%) with outside temperature and the
motor is sized to handle the worst case situation. In air conditioners
any wasted motor heat is paid for at a premium in that you have to
provide additional cooling (use more power) to get rid of that heat.
I'm thinking of piston type compressors where the motors run at the same
speed regardless of load which means they are loafing along much of the
time.
Of course even better would be modern compressors capable of running at
two speeds and which also give better humidity control and more constant
supply temps as well. I can't think of any residential use other than
air conditioners and heat pumps where I would even bother to test one of
these "energy saving" devices.
Ken
Robert L. Nuckolls, III wrote:
| Quote: |
<nuckolls.bob(at)aeroelectric.com>
At 03:25 PM 12/12/2009, you wrote:
>
>
> Perhaps I'm dated but most capacitor start motors only used the
> capacitor to get a phase change for starting. The capacitor did not do
> anything for running PF correction IIRC. Have things changed?
No . . . digging around in the gray matter seems to
dredge up some things I used to teach about induction
motors at Great Lakes. The capacitor(s) on a motor
are for starting (the BIG guy) paired with the
occasional second, smaller device for running.
My central air conditioners and shop air compressor
are fitted with a pair of Start/Run capacitors.
And you're right, those capacitors are selected for
optimized rotation of a magnetic field in the stator
when only single-phase power is available. They're in
series with one or more windings and NOT for PF correction.
P.F. correction needs to be in parallel with the main
winding.
So, depending on how high the resistive losses in
the main winding, there could be some significant
degradation of power factor. But the motor guys
are as sensitive to temperature rise due to I(squared)*R
as are the guys who transformers and other wiring.
They'll do what economically practical to minimize
said losses.
I think one of the articles that were cited over
the past few days suggested that average power
factor for a home was .90 . . . so it would be
difficult to realize much savings in I(squared)*R
R losses when the majority of said losses are
spread over ALL the building's distribution system.
Bob . . .
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Dennis Johnson
Joined: 10 Jan 2006
Posts: 89
Location: N. Calif.
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| Posted: Mon Dec 14, 2009 9:44 am Post subject: Power Opti-Miser |
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My house is not connected to the power grid, which makes me both a power generator and a power consumer. If we look at this issue from that perspective, things change.
Let's say I install some compact fluorescent lights to save electricity. Assume I have the misfortune to select ones with a bad power factor. If I were connected to the power grid, my electrical meter would measure real watts, which in this case is 70 watts for all the lights I installed. That's a big savings over the tungsten filament lights I removed. So far, so good.
But since I'm my own power producer, I have to make enough extra electricity to accommodate the lousy power factor. In this case, let's say the power factor is 0.7. That means I have to make 100 watts of apparent power to run my 70 watts of compact fluorescent lights. Still a savings over the tungsten bulbs, but not as much as expected.
I have measured the actual amperage taken out of my battery bank to power compact fluorescent lights and these numbers are in the ballpark. I want to warn everyone that I have no background in electrical engineering but have had a lifelong tinkerer's interest in it and studied everything I could find when designing and installing my off-grid solar home. So I could be way off here, and hope I'm corrected if I'm wrong about any of this.
My conclusion is that both sides of this camp might be at least partially correct. Since residential power meters measure real watts, the residential consumer isn't penalized for the extra power the utility has to generate to run bad power factor appliances. Therefore, the residential consumer shouldn't expect to see any savings on the utility bill.
However, the utility has to generate the extra electricity, even though they aren't getting paid for it (which is already built into the rate structure). But if consumers could do something to improve the power factor of their appliances, it would reduce the amount of electricity produced, reducing the unfavorable environmental consequences of making electricity. That would be good for everyone (assuming the environmental effects of making the correction devices resulted in a net gain, of course).
I have no opinion as to whether the devices under discussion actually reduce apparent watts. It may well be that the most recent appliances include better internal power factor correction. I know that the last batch of compact fluorescent bulbs I bought seem to have very good power factor.
Dennis
Long-time Home Power magazine subscriber http://www.homepower.com/home/
Wikipedia power factor reference: http://en.wikipedia.org/wiki/AC_power
[quote][b]
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Tue Dec 15, 2009 6:10 pm Post subject: Power Opti-Miser |
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At 11:30 AM 12/14/2009, you wrote:
| Quote: | My house is not connected to the power grid, which makes me both a
power generator and a power consumer. If we look at this issue from
that perspective, things change.
|
<snip>
| Quote: | My conclusion is that both sides of this camp might be at least
partially correct. Since residential power meters measure real
watts, the residential consumer isn't penalized for the extra power
the utility has to generate to run bad power factor appliances.
|
| Quote: | However, the utility has to generate the extra electricity, even
though they aren't getting paid for it (which is already built into
the rate structure).
|
The utility doesn't have to generate any extra watts. It only has
to choose wire sizes that carry an artificially high current that
doesn't participate in the running of devices with poor p.f.
| Quote: | But if consumers could do something to improve the power factor
of their appliances, it would reduce the amount of electricity
produced, reducing the unfavorable environmental consequences of
making electricity. That would be good for everyone (assuming the
environmental effects of making the correction devices resulted in
a net gain, of course).
|
The "goodness" comes only from the fact that the same work
can be done over smaller wires with less heating of the
wires. A significant savings when your transmission lines
are measured in miles instead of feet and transformers are
in 100's of KVAR instead of 2 KVAR.
| Quote: |
I have no opinion as to whether the devices under discussion
actually reduce apparent watts. It may well be that the most recent
appliances include better internal power factor correction. I know
that the last batch of compact fluorescent bulbs I bought seem to
have very good power factor.
|
Yes. And the folks who do switchmode power supplies
for computers and other electronics have been prodded
by dozens of articles for how p.f. can be improved for
over 20 years.
See chapter 11 in Volume 2 of the basic electronics
document below . . .
http://www.allaboutcircuits.com/vol_2/index.html
If your AC power generation devices are pseudo sine
wave (finely stepped square wave) then the output
power has more harmonic content than the stuff
coming out of the wall. This puts a whole new
twist on the problem of optimizing power factor.
Have you measured the aggregate power factor for
household loads on your system? It may well be that
the losses are so small that doing anything about
them is economically impractical. When talking about
small losses, keep in mind that your house wiring
is not zero ohms material. Depending on how long
the runs are, you may find that copper losses
are already significant and only slightly aggravated
by the effects of p.f.
Lord Kelvin reminded us often that without access
to the real numbers, our knowledge is of a meager
kind.
Your situation cries out for a long term study
of aggregate quality for your total household load.
A true RMS voltmeter, ammeter and power-factor meter
recording to a hard drive over a long period of time
would give you a basis for doing more detailed
studies followed up by useful changes to your
hardware.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Mon Dec 21, 2009 7:34 pm Post subject: Power Opti-Miser |
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At 12:55 PM 12/10/2009, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Eric M. Jones" <emjones(at)charter.net>
Yes, indeed it is possible and even money saving to use such a device. I was initially puzzled how little technical stuff there was, but then I remembered that NASA worked on, published and licensed everything in the early 1980s. (Patent + 20 years...hey!).
Power-Miser technology was a big deal then: Google "Power Miser NASA" and you will get lots of info. Or search the old NASA archives or patents around 1980.
The way the thing works is er...ah...well...I think it might change the power factor to match the load. I did a lot of work on power factor correction and I can assure you saving money is possible. This works only on inductive loads as far as I remember.
The product is real, and so is the money savings. How long it takes to pay off the device varies. |
THAT IS the big question. Given that improvements
in performance are achieved by improvements in
I-squared*R losses, then savings to be realized
are a function of just how "bad" the "bad" system is.
Most household motor loads tend to be small and
intermittent. Further, these loads have enjoyed
incremental improvements in efficiency over the
years. Bottom line is that if ALL the badness of
a stock system can be compensated for, the savings
are NOT going to be more than a few percent and
that's for devices which contribute to overall
"badness". If these loads are intermittent,
then the savings is multiplied by some duty
cycle that is less than 1.0.
Bottom line is, don't pay much for any such device
without having solid measurements that predict
improvements with an acceptable return on investment.
See:
http://tinyurl.com/3pbopt
P.S. Just because NASA did it does not make it
"golden" . . .
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
[quote][b]
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rjquillin
Joined: 13 May 2007
Posts: 123
Location: KSEE
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| Posted: Thu Dec 31, 2009 9:02 am Post subject: Power Opti-Miser |
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At 18:05 12/15/2009, you wrote:
| Quote: | The utility doesn't have to generate any extra watts. It only has
to choose wire sizes that carry an artificially high current that
doesn't participate in the running of devices with poor p.f. |
A year end article summary from an e-rag I read had a short commentary on PF issues that may be of some interest...
Sorry I didn't recall it earlier in the thread.
Ron Q.
http://www.edn.com/blog/1470000147/post/450043045.html?nid=2431&rid=1968165
[quote]Monday, April 6, 2009
Utilities suffer from CFLs’ poor power factor
Apr 6 2009 6:00PM | Permalink | Comments (96) |
Every CFL light contains a small ac-dc power supply with reactive components in it that will affect the CFL’s power factor (PF) – that is, the load presented to the ac line. The closer the PF is to 1, the better. A load with low power factor (<.85) draws more current and is less efficient than a load with a high power factor for the same amount of useful power. The higher currents required by the lower PF devices mean increased energy lost in the grid due to such things as I2R losses. These power losses don’t show up directly on our electricity bill, but the utilities sure see the effects.
I put one of my home CFL bulbs on my Kill-O-Watt power meter recently and measured its power factor: It was .57. This is lousy. Although each CFL is only 13W, there are millions of them out there. Why no PF regulation, as there is of higher-power, but less ubiquitous devices?
I emailed Peter Banwell of the EnergyStar program and asked if EnergyStar was considering making minimum PF a requirement for Energy Star compliance. He replied, “We looked at this in detail several years ago and decided against it, though there are a couple of utilities that still support the idea. We may take this up in the future, as the market share grows, but right now it is still in the noise in terms of impacts.”
Coincidentally, after our email exchange I ran into Mike Grather of Luminaire Testing Laboratory. He recently ran a series of life-cycle and performance tests on a batch of 100 CFLs with various power ratings averaging approximately 20W each. They assumed a PF for the lights of at least .75 and sized the power supply at 3KVA. However, when they powered up the bank of CFLs, the 3KVA supply was inadequate. Grather checked the power factor for the CFLs and found they ranged from .45 to .50. Their “real” load was about twice that implied by their wattage.
CFLs are still an efficient form of household lighting, but their poor PF number is leaving money on the table. However, it’s clear that at about $2 each there’s not a lot of room for adding power factor correction circuitry. On the other hand, utilities are already going to great lengths to encourage consumers to switch to CFLs, including subsidizing the price of CFLs. I doubt that consumers would be interested in paying more for a feature that actually benefits the utility directly, not them. Perhaps utilities will start to subsidize high-power-factor CFLs, rather than the mediocre ones we can buy now.[b]
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