Does anyone manufacture a "variable heat" electric range, where when you
select the heat setting, it would have a constant heat at a certain
temperature? (Like you can do with a gas range...)
This would be sort of like a dimmer switch for a light where you can adjust
how much light is output from the bulb.
The way electric ranges work now is they go on and off, on and off.
Less heat means the "burner" goes on for a little while, then off for quite
awhile. Then with more heat, the "burner" is on for a long time, then off
for a little amount of time.
With a gas range, you can adjust the heat so it is constant - no off and on.
Seems they could do this with an electric range as well....
There are electronic thermostats for electric heating applications
that modulate output (I have some from Aube that control with my
in-floor radiant heat), but they're fairly expensive. I suspect their
high cost and perhaps concerns related to long-term reliability would
limit their use elsewhere. Variable wattage control would be a nice
feature from the utility's point of view (i.e., by smoothing out
demand), but I suspect most consumers wouldn't care one way or the
This makes no difference to the utility, because they have thousands
of stoves and similar loads, which are all randomly cycling on and
off, effectively averaging it all together, so smoothing out demand
from one stove doesn't do anything. They would never see it.
The reason its done the way it is on electric ranges is it's a cheap
mechanical switch, that cycles it on and off for varying periods.
To make the heating more even would require turning it on and off
rapidly, which is what is done in wall switch dimmers, which do it on
each AC cycle. That requires electronics. And to do that for a
dimmer, which is 600W max, takes a smaller, less expensive
semiconductor than it would require for a range. It's possible
someone offers it, but I haven't seen one.
I'm not so sure about that. My utility, Nova Scotia Power, like
virtually ever utility here in Canada, is winter peaking and these
peaks typically occur around 17h30 when street lights start coming on
and electric ranges are being used to prepare evening meals.
**Anything** that helps minimize concurrent demand, no matter how
small, would be helpful from the utility's perspective, especially in
light of the high percentage of homes that are electrically heated in
Let's say the average electric oven draws 3.0 kW (my convection oven
happens to be 5.5 kW). We might expect the typical household oven to
operate at full power for the first ten minutes or so, then cycle on
perhaps one third of the time thereafter (i.e., an average of one
minute on for every two minutes off). Let's also assume there are
100,000 electric ovens in use province-wide during the suppertime peak
(and here in Nova Scotia, virtually all ovens are electric since only
500 or so homes are currently served by natural gas).
If all 100,000 ovens were energized at the same time, we would expect
this load to be 300 MW. We're assuming, of course, that as each of
these ovens come up to temperature, the actual load at a 33% duty
cycle, would be closer to 100 MW, and since these ovens are not all
turned on at the same time, a coincidental peak of 100 MW is probably
within spitting distance of the mark. If, however, each of these
ovens were equipped with variable wattage controls and, again,
assuming a 33% duty cycle, our coincidental peak should drop to just
On a typical winter's day, Nova Scotia Power's peak falls between
1,500 to 2,000 MW, so a 67 MW reduction in provincial demand would
represent a peak savings of perhaps as much as 3 to 5 per cent. In
theory, it would exceed the province's total installed wind capacity
of some 60 MW (which, assuming a 40 per cent annual capacity factor, I
take it might be closer to just 25 MW). Even if we were to cut the
number of ovens in operation by half, the impact on a utility such as
Nova Scotia Power is not exactly insignificant.
On 12 Feb 2007 07:49:37 -0800, firstname.lastname@example.org wrote:
This also means that you have eliminated the normal full on heating
mode of the oven and reduced it to 1/3 of that. Which means now
everyone has to wait 3X as long for the oven or burner to warm up,
which few people are going to put up with. After that, the oven or
burner will be cycling randomly anyway and the sum of them all cycling
randomly is the same And presumably, this cooking load comes late in
the day, like 6PM+, which is after industrial/commerical use is
decreasing. With all the other loads I fail to see how this is going
to make any difference in the generating capacity needed to meet peak
demand or save the utiltiy even 5cents. It will mean a lot of pissed
off users though, who can't get their oven hot in a reasonable time.
So, you have just as many ovens running longer. Unless you have
proof that ovens are causing a peak demand that results in either
higher capital cost for generators to meet peak capacity or are
causing the need to kick in some higher cost energy source during
dinner time, this is just a pipe dream.
On 12 Feb 2007 11:12:27 -0800, email@example.com wrote:
No, please go back and re-read what I said; to whit:
"We might expect the typical household oven to operate at full power
for the first ten minutes or so, then cycle on perhaps one third of
the time thereafter..."
"If all 100,000 ovens were energized at the same time, we would expect
this load to be 300 MW. We're assuming, of course, that AS EACH OF
THESE OVENS COME UP TO TEMPERATURE, the actual load at a 33% duty
cycle, would be closer to 100 MW, and since these ovens are NOT all
turned on at the same time, a coincidental peak of 100 MW is probably
within spitting distance of the mark...."
So there are two key points here:
a) the load on our utility during the suppertime peak is minimized
due to the cycling of these elements at what I had estimated
to be 33% and, secondly,
b) due to the fact these ovens are not all turned on at precisely
the same time, the impact of that first ten-minute start-up
is thereby diminished.
Nowhere did I say these ovens would operate at reduced power upon
start-up. Each could continue to operate at full power for as long it
takes to come up to temperature, then drop to the lowest wattage
required to maintain a constant set temperaturer; if the oven element
is rated at 3,000 watts and it normally cycles on one-third of the
time, then it's fair to say a constant 1,000 watts is all that's
needed to maintain a steady temperature from this point forward.
There would be absolutely no inconvenience to the consumer whatsoever
and the utility would still benefit from reduced aggregate load.
You claim these ovens would run longer but as I indicated above, they
won't. In any event, according to U.S DOE EIA, the generating
technology with the lowest capital cost would be a 230 MW advanced
combustion turbine at a cost of $US367.00 per kW (O&M and T&D extra).
Thus, if we can effectively reduce peak demand from by just ***ONE***
MW, the capital savings to the utility is a minimum of $367,000.00 US
($436,730.00 CDN); at 67 MW, the savings amount to $CDN 29.3 million.
To this you would add the additional operational and maintenance costs
(and this *is* the single most expensive way to generate electricity
by conventional means), plus the added transmission and distribution
expenses. Also, bear in mind, the utility continues to sell the same
amount of energy as before, so there's no resulting loss in revenue,
BUT it does get to pocket all these other savings.
No, the load on the utility (averaged over 100000 houses) is still 100
MW, no matter whether the ovens elements are cycling on and off every
1/120 sec or every 2 minutes. Because of the randomness of the
mechanical thermostat open/close, you'll never get more than about 1/3
of those ovens on at any one instant.
In fact, I will bet that the utility would be mightily *unhappy* to
have 100 MW of load all switch on for the last 1/3 of every half-cycle
of the line. That will distort the waveform on the grid.
But you haven't reduced peak demand at all. In fact, you've increased
it slightly due to losses in the triacs of the electronic control, and
distorted the current waveform.
OK, thanks for walking me through this, one step at a time; appreciate
your help. If I've got this right, with such a large number of ovens
in use, we can reasonably assume no more than one-third of these
elements will be energized at any one time, regardless of the length
of each "on" cycle, be it 1/120 of a second or one to two minutes. I
had envisioned this load would be more variable at these longer cycles
and that we could, in effect, "chop peak" and "fill valley" by slicing
it into increasingly finer increments. Perhaps with just 100 ovens
that might be possible, but with 100,000 it would make no discernable
difference. That seems to makes sense.
In terms of ensuring high power quality (and reduced appliance cost),
one alternative might be dual-wattage elements. One high power
element for quick start-up and a second, low-density companion that
would maintain the oven at its set temperature (similar to how some
hot water tanks operate). If, for whatever reason, this secondary
element couldn't keep up (e.g., repeated door openings), it would
temporarily throw things back to the primary element, then once again
resume command; it would still cycle on and off as required, but it
would be sized to more or less to run continuously and minimize any
further need for its bigger brother.
While such an arrangement might not reduce peak demand, it could still
offer some benefits in terms of reducing the strain on the local
distribution system. Would that sound reasonable?
On Tue, 13 Feb 2007 01:53:38 +0000 (UTC), firstname.lastname@example.org (Dave
Many (most?) electric ovens already do this. The pre-heat stage
energizes both the bottom and broiler elements. The idea, though, is
to pre-heat the oven faster, not to help the power company balance
My apologies for asking this, but is this something relatively new or
has it always been this way? I don't have a lot of experience with
electric ovens because I've always used gas, but this time around I
had to settle for a combination unit because an all gas version wasn't
I did experiment with mine just now and here's what I found. There
are basically three heating options I can choose: "bake", "broil" and
"convection" and as far as I can tell all three work independently of
each other. When I turn on "broil" I can safely leave my hand on the
lower bake element and it remains cool to the touch; likewise, the
broiler never comes on when I select "bake" and neither of these two
elements are used when I pick "convection" (that appears to be a third
element hidden somewhere inside the oven's back wall).
In any event, this second element arrangement I had imagined would be
used in bake (or convection) mode and would be very low wattage --
just the minimum required to maintain a steady operating temperature
and effectively "lock out" the primary element that is used during the
initial warm-up. It may be that we only need 500 or 1,000-watts
during this extended cooking phase to keep things moving along.
There doesn't appear to be any real benefit in terms of utility-wide
peak shaving (sorry to say it took a couple blows to the head to drive
that point home), but there may be some benefit in terms of reducing
the strain on the local distribution system. If, for example, my
neighbour and I share the same pole transformer and our ovens both
cycle on at roughly the same time (and we can safely assume there will
be at least some overlap during their operation), the combined load of
these two appliances might be 6 or 8 kW. However, if we don't turn
our ovens on within ten minutes of each other (i.e., during that
initial warm-up phase), with this dual wattage arrangement, our
combined load may never exceed 4 or 5 kW and our steady-state
operation may drop to just 1 or 2 kW.
It would seem that as we move closer to the point of use (i.e., from
sub-station/feeder to local line, to individual pole transformer) the
potential benefits to the utility become increasingly more attractive.
And in the case of a large condo or apartment complex, I imagine the
potential load reduction could result in some capital savings (i.e.,
smaller service requirements) and perhaps reduced monthly demand
charges. Ideally, if dual wattage elements added an extra $50.00 to
the cost of each appliance, this extra cost would be fully offset by
these other capital savings and any additional savings in terms of
reduced monthly demand charges would simply add extra gravy in the
On Tue, 13 Feb 2007 06:43:18 -0600, Mike Hartigan
And how are you going to coordinate not turning on ovens with your
neighbor at the same time? Use a flag hanging out the window?
This is simple physics. If you expect to limit the power, then the
oven isn't going to heat up as fast. And that could be solved just as
simply by just putting in an oven element that was say 25% smaller to
begin with. You really only need the max when you're trying to take
the oven from cold to operating temp. After, that, it cycles anyway
and could easily get by with probably 1/2 the existing element
capacity. Of course the downside is that instead of waiting 15 mins
for the oven to heat up, now you're gonna wait a half hour and few
people will put up with that to solve a problem that doesn't exist to
with this dual wattage arrangement, our
You still don't get it. The amount of energy that it takes to
operate an oven is independent of whether you have 1 element or 40.
You could have a 4000 watt element on for 15 mins or a 2000 watt
element for 30 and it uses exaclty the same amount of energy. You
can't just decrease the steady state amount of power and have the oven
be just as hot.
You're focusing on one small nit here and ignoring everything else.
Condos typically have all kinds of loads, AC, heat pumps, furnace
blowers, electric water heaters, etc. Reducing some oven power
isn;t going to be a big factor that now means smaller gauge wire or a
smaller transformers can be used. And to reduce the oven loads,
what you fail to realize is that you are either asking people to:
a - Wait longer for their ovens to warm up, because the power into
them is being reduced to limit peak during start up.
b - Hang flags out the window so unit A can't start cooking dinnner at
the same time as unit B
Who is going to put up with that?
Ideally, if dual wattage elements added an extra $50.00 to
What reduced monthly charges? You still need the same amount of
energy going into the oven to make it hot. In fact, your idea could
take MORE energy. By reducing the max power, its' going to take
longer for the oven to get to 400 deg. While it's talking the extra
10 or 15 mins, heat is being lost out of the oven throught the walls,
or even worse, people opening the door to see what's going on.
When I was a kid (1960's), our old Frigidaire did this. Today (still
a kid only bigger), our new Thermador does this. (ours is dual fuel,
not because all gas wasn't available, but because we wanted the
advantages of dual fuel.)
Our Thermador uses the upper for broiling (duh!), both the upper and
lower to preheat, switching to lower only to maintain temperature.
The convection setting has its own element.
That's interesting. I wonder if your Thermador being dual fuel works
a little differently from your standard, run of the mill electric
range. We have a dual fuel Heartland Legacy, but the original range
(another Frigidaire) was all electric and the circuit supplying it is
equipped with a 40-amp breaker which, for the moment, I'll assume is
the norm. If we abide by the 80 per cent rule and assuming a full 240
volts, that gives us roughly 7,700 watts to work with.
A standard 30-inch range would have four cook-top burners and two oven
elements (bake and broil). I guess the question we must ask ourselves
is do we have enough capacity at 40-amps to supply all or a reasonable
combination of these elements without tripping the breaker? I realize
it's not likely we'd have all four burners turned on high and the oven
pre-heating, but it would be interesting to see just how far we might
push our luck.
Quoting from the Whirlpool's website, "Electric coil ranges usually
have two high-output elements (8-inch coils rated 2,600 Watts) and two
low-output elements (6-inch coils rated 1,500 Watts)." Using these
numbers, if all four burners were turned on high, our combined load
would be 8,200-watts (34 amps) or just slightly over 85 per cent of
our circuit's capacity.
Now I'm guessing a standard bake element is 3,000-watts and a broil
element is about the same or perhaps a little higher. If we assume
the two elements total 6,000-watts, we stand at 25 amps or just a
little over 60 per cent of total capacity.
If we have our two large burners turned on and both oven elements
operating, demand exceeds 11,000-watts (47 amps) and our breaker
trips. However, these same two burners and just the bake element
drops us back down to 8,200 watts/34 amps which should keep the power
So, realistically speaking, operating both oven elements on a 40-amp
circuit doesn't seem feasible. With dual fuel, it won't be a problem
but with an all electric range, you would have to bump things up to 50
or even 60 amps. Any idea what size breaker is normally used for a
standard 30-inch range? I'm guessing 40 only by what I see in my own
panel, but perhaps 50 or 60 amps is more common.
On Tue, 13 Feb 2007 22:00:36 -0600, Mike Hartigan
On Wed, 14 Feb 2007 05:51:08 GMT, Paul M. Eldridge
What I have here is built-in, where the oven and cooktop are separate
units. Each unit is on a separate 30A breaker.
The coils on the cooktop are the same size you mentioned (2 6 inch and
2 8 inch). That would seem to mean that would all require 35A. I have
had all 4 on high and it hasn't tripped the breaker.
That breaker (Square D) has a red trip indicator that is visible no
matter what (on of off, I've never had it trip). Could it be
Good question. I wonder if any of these burners are lower in wattage,
even though they're of the same physical size. Is there anything
stamped on the burner itself (e.g., at the prong ends) that might
indicate their wattage or do you happen to have the owner's manual?
At the outer edge, thirty amps at 240-volts provides us with a maximum
of 7,200 watts and the 80 per cent rule drops us down to just 5,760
watts. Your breaker might tolerate some minor, short-term overloading
(I honestly don't know), but four burners on high must be pushing that
30-amp circuit pretty hard, especially if your supply voltage should
fall much below 240.
On Wed, 14 Feb 2007 12:24:24 -0600, Mark Lloyd
My built-in oven (old Frigidaire electric) uses both elements when
baking. I found out then the upper element quit working (not a bad
element, but the connector). Food would burn on the bottom and still
be raw on top.
No, it doesn't sound reasonable, because, as Dave and I have
repeatedly tried to explain to you:
1 - In your example, with 100,000 stoves cycling on and off randomly,
the load is already randomly distributed, at least after the initial
heat up period of 15 mins or so. You can use one element, two
elements, or 300 elements and it doesn't do anything to affect the
peak load or power distribution as long as the heating elements are
the same size and the duty cycle is the same.
2 - Assuming a lot of ranges/ovens come on around 5-7pm, if you wanted
to reduced the load at this time, you can do it by either:
a - Using smaller heating elements
b - Keeping the duty cycle from being 100% during the heat up period.
Either of those will reduce the heating capacity of the stove.
Option a permanently and option b during startup, meaning the oven
will take longer to get hot.
And I think the problem you're trying to solve here doesn't exist to
begin with. There are generally two problems that utilities are
concerned with regarding peak demand. One is they need a generator
and system big enough to handle the peak, requiring more capital
investment. And/or they need to buy power from somewhere else during
peak time and that power may cost more. AFAIK, none of these issues
typically occurs at 5-7PM due to home ranges. Around here, they
typically occur during very hot summer afternoon periods, when
commercial use is high and everyone has their home AC units running,
etc. Most people don't have their ovens going then, because it's hot
and they aren't planning on making a roast turkey to make the house
On Tue, 13 Feb 2007 01:53:38 +0000 (UTC), email@example.com (Dave
There's nothing to prevent all of then from switching on at the same
moment. The chance of this happening at times will be nearly 100%.
Peak demand is still 300MW, but most peaks can be expected to be very
short. Well within the utility's capability.
There is no *technical device* to prevent them all from coming on at
once. But the simple statistics of the situation mean that almost all
the time, the number of ovens drawing power is 1/3 of the total plus or
minus a few percent. The odds of having all of them on at once is
incredibly tiny, so tiny that nobody would estimate or plan a peak load
based on that event.
Just look at the probability distribution of a 100,000 random events
each with a probability of being on of 1/3. The odds of having exactly
33,333 of them on is quite small, but the odds of somewhere between 30
and 35000 being on is nearly 1.
On Tue, 13 Feb 2007 20:06:58 +0000 (UTC), firstname.lastname@example.org (Dave
That's a very common statistics mistake. That gives you the
probability that all stoves are on at a particular time. What matters
is if all stoves are on at ANY time. There's a really big difference
there (as big as the difference between a millimeter and the width of
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