(Joe Doe) wrote in message ...
I do not believe everything CR says. Their interpretation is one
interpretation (and could be a contributing factor). In general I doubt
their competence. For example they assume that the manufacturers quoted
9000 BTU is OUTPUT BTU. This is guaranteed not to be true. If it were
true, water would boil faster than their quoted figures. So even though
they are supposed to be semi-competent they make mistakes as laughable as
this. So while I think they can put a pot of water on a stove and measure
the time it takes to boil that is about all I think they can do. They
also slam some burners because they cannot maintain a simmer. This is
laughable to any competent cook - simply add a flame diffuser. While it
is desirable in terms of energy efficiency to match a burner to a task, it
is silly to create a non-existent problem (simmer function) and by the
power of their bully pulpit cause manufacturers to make a less versatile
burner.

In support of my original point that burner efficiencies are important see:

http://www.epri.com/journal/details....ctype=features

This is an article by the electrical power research institute pushing an
induction burner but it shows that commercial gas burners only have 30%
efficiency and residential 47%. Scroll to about the bottom third of the
article to find a bar graph showing the efficiencies. This is also
repeated in the text of the article where they say: "The Luxine unit had
a energy efficiency of 92%, compared to 72% for the radiant electric
range, 47% for the residential gas range, and 30% for the commercial gas
range".

This data supports my point nicely - the 20,200 BTU commercial range would
put out 6060 BTU of heat while the 9500 BTU residential would put out 4465
BTU. So the difference between the commercial and residential is 35%
instead of the naive expectation of a 100% difference. The consumer
reports article I was thinking of, had a GE profile with a 12,500 BTU
burner beating a DCS with a 15,000 BTU burner. To me efficiency seems the
most likely reason why the DCS performed poorly.

I have come across these kinds of figures in other searches (research done
mainly by utility companies promoting energy efficiency) wrt to commercial
burners so I believe it. More efficient commercial burners exist, but as
I pointed out you actually need to know the efficiency of the burner under
consideration to make meaningful comparisons between lines. Since this
seems to never make it out in the specification sheets, we can only guess.

Incidentally gas furnace manufacturers are more forthcoming - they
frequently cite Input BTU, Output BTU and Efficiency

Roland

Roland, thanks for the link to the very informative article. I'd just
like to point out that the EPRI article talks about "cooking
efficiency". That's a little different than "efficiency" in the sense
if input and output BTU's. Unlike, for example, a furnace where you
have so many BTU's input and so much hot air coming out and input and
output BTU's are different, every burner that completely burns gas
(i.e., doesn't leave significant unburned hydrocarbons or produce
carbon monoxide - in other words all burners, we hope) is by
definition 100% efficient. In other words, input and output BTU's are
the same for any burner. If you burn a certain volume of natural gas
or LPG, you get a certain amount of heat. Period.

The question is whether the heat makes it in the pan or not - *that's*
what the EPRI article is talking about when they use the term "cooking
efficiency. " Electric "burners" whether induction or even ordinary
ribbon elements excel at this because the close contact to the pan;
most heat ends up in the pan and little in the room. Gas burners are
obviously quite different - you need room for the flame, heated air
runs up the sides of the pan and you actually get more heat in the
room than into the pan.

Anyway, that's why you don't see numbers like input versus output BTUs
or efficiency for cooktops - the former are always the same and the
latter is always 100%. It's not that cooktop manufacturers are less
"forthcoming" than furnace manufacturers. It would be nice if what
the EPRI article calls "cooking efficiency" but of course that is
highly dependent things like on size of the pan that are some degree
out of the manufacturer's control.

- Mark W.

In article ,
(Mark Willstatter) wrote:

Roland, thanks for the link to the very informative article. I'd just
like to point out that the EPRI article talks about "cooking
efficiency". That's a little different than "efficiency" in the sense
if input and output BTU's. Unlike, for example, a furnace where you
have so many BTU's input and so much hot air coming out and input and
output BTU's are different, every burner that completely burns gas
(i.e., doesn't leave significant unburned hydrocarbons or produce
carbon monoxide - in other words all burners, we hope) is by
definition 100% efficient. In other words, input and output BTU's are
the same for any burner. If you burn a certain volume of natural gas
or LPG, you get a certain amount of heat. Period.

- Mark W.


Actually, burner combustion efficiency is never 100% For example see an
article in ³Appliance Manufacturer² which states combustion efficiency is
in the range of 70-85% (so it could vary between manufacturers).

http://www.ammagazine.com/CDA/Articl...,85072,00.html

They state: ³A typical open-top burner can easily attain combustion
efficiencies of 70 percent to 85 percent. However, when you test the same
system using a water boil test, the System Thermal Efficiency (STE) is
usually between 25 percent to 35 percent. Where are the losses occurring?
And how can we increase the STE using an intelligent engineering
approach?²

I will sheepishly admit, that I thought that combustion efficiency was
fully capturing what you call ³cooking efficiency² and they call STE and I
underestimated the impact of heat transfer efficiency (which you correctly
emphasize).

Nonetheless, the bottom line in my original point is still valid: you
cannot simply take BTU delivered to the burner and assume it will be
delivered to the pot. So without knowing STE (combustion efficiency X
heat transfer efficiency) you cannot compare ranges based on raw BTU.
As this article demonstrates, the reasons why it is not transferred to the
pot are complex and include burner geometry, grate geometry, gas dwell
time, excess air etc. (and my favorite combustion efficiency ,).

So the number that a manufacturer should quote is the STE and in the
absence of that, the only measure a consumer has is to get the actual time
it takes to bring a large volume of water to a boil, which CR does.
Maybe manufacturers should quote how long it takes a burner to bring 2
gallons of water to a boil as an easily understood number that would
capture STE. Absent this, I do not know how one can compare across
manufacturers.

Maybe it would be useful for other readers, if people who have powerful
burners could report the time it takes to bring 1 or 2 gallons of water
to a boil (as measured by a thermometer). In this way we could have a
ballpark idea of the true power of all the commercially available ranges
that are peoples favorites.

Roland

(Joe Doe) wrote in message ...


Actually, burner combustion efficiency is never 100% For example see an
article in ³Appliance Manufacturer² which states combustion efficiency is
in the range of 70-85% (so it could vary between manufacturers).

http://www.ammagazine.com/CDA/Articl...,85072,00.html

They state: ³A typical open-top burner can easily attain combustion
efficiencies of 70 percent to 85 percent. However, when you test the same
system using a water boil test, the System Thermal Efficiency (STE) is
usually between 25 percent to 35 percent. Where are the losses occurring?
And how can we increase the STE using an intelligent engineering
approach?²

I will sheepishly admit, that I thought that combustion efficiency was
fully capturing what you call ³cooking efficiency² and they call STE and I
underestimated the impact of heat transfer efficiency (which you correctly
emphasize).

Nonetheless, the bottom line in my original point is still valid: you
cannot simply take BTU delivered to the burner and assume it will be
delivered to the pot. So without knowing STE (combustion efficiency X
heat transfer efficiency) you cannot compare ranges based on raw BTU.
As this article demonstrates, the reasons why it is not transferred to the
pot are complex and include burner geometry, grate geometry, gas dwell
time, excess air etc. (and my favorite combustion efficiency ,).

So the number that a manufacturer should quote is the STE and in the
absence of that, the only measure a consumer has is to get the actual time
it takes to bring a large volume of water to a boil, which CR does.
Maybe manufacturers should quote how long it takes a burner to bring 2
gallons of water to a boil as an easily understood number that would
capture STE. Absent this, I do not know how one can compare across
manufacturers.

Maybe it would be useful for other readers, if people who have powerful
burners could report the time it takes to bring 1 or 2 gallons of water
to a boil (as measured by a thermometer). In this way we could have a
ballpark idea of the true power of all the commercially available ranges
that are peoples favorites.

Roland

Roland, so we were both screwed up - let's call it even ;^) I can't
take credit of the term "cooking efficiency" - it came out of the
article at the link you gave in your previous post. Even if not 100%,
as your article points out, the biggest variable is not combustion
efficiency but what they call "heat transfer efficiency". I'd still
say it's not too reasonable to expect manufacturers to quote a number
since so much is involved in STE, in particular the size and type of
pan. Particularly with sealed burners, size of pan is critical since
the flame pattern on 'High' can easily exceed the diameter of a pan.

There was once a thread of the sort you mention at the following site
but I don't believe they rchive and I think it's disappeared:
http://ths.gardenweb.com/forums/appl/. There were some definite
surprises, as you say, all burners of the same rating are not created
equal. Getting good data was difficult since people's conditions
varied so much. The only thing lending the thread some credibility
was the fact that one guy was somehow able to test a number of
cooktops using his own consistent methodology. If you have multiple
testers involved, you need to settle on standards: size and
construction of pan, lid on or not, starting temperature of the water,
how boiling at the end (you solve this with the thermometer but would
probably want to set a temperature below sea level boiling point so
those at altitude could contribute), even ambient temperature.

- Mark w.

Even if not 100%,
as your article points out, the biggest variable is not combustion
efficiency but what they call "heat transfer efficiency".

- Mark w.

If you really want to improve the efficiency of your burners, buy cookware
that is highly efficient... :-) Seriously! Falk, Mauviel or Bourgeat...

--
Michael Harp
http://CopperPans.com

Michael Harp wrote in message ...
Even if not 100%,
as your article points out, the biggest variable is not combustion
efficiency but what they call "heat transfer efficiency".

- Mark w.

If you really want to improve the efficiency of your burners, buy cookware
that is highly efficient... :-) Seriously! Falk, Mauviel or Bourgeat...

I think the most important factor is just a reasonable match of pan
size with burner. Particularly if we're talking about a sealed burner
with the around the periphery, it's easy to have the heat close to the
edge of the pan or beyond. As the article mentioned, for efficiency
purposes it's important to get the heat as near to the center of the
pan as possible. That means small diameter burners and/or wide pans.
The construction of the pan is also important but some distance down
the list compared to that. I suspect any pan with a decent volume of
aluminum or copper in the bottom would do fine.

On 10/1/03 17:49, in article
, "Mark Willstatter"
wrote:

Michael Harp wrote in message
...
Even if not 100%,
as your article points out, the biggest variable is not combustion
efficiency but what they call "heat transfer efficiency".

- Mark w.

If you really want to improve the efficiency of your burners, buy cookware
that is highly efficient... :-) Seriously! Falk, Mauviel or Bourgeat...

I think the most important factor is just a reasonable match of pan
size with burner. Particularly if we're talking about a sealed burner
with the around the periphery, it's easy to have the heat close to the
edge of the pan or beyond. As the article mentioned, for efficiency
purposes it's important to get the heat as near to the center of the
pan as possible. That means small diameter burners and/or wide pans.
The construction of the pan is also important but some distance down
the list compared to that. I suspect any pan with a decent volume of
aluminum or copper in the bottom would do fine.

You're absolutely correct about matching flame patterns to pan sizes, which
is why I am a big fan of the star-type burner designs (Garland/Bluestar,
even Thermador?) and not a fan of the circular patterns. The former
mitigate the problems with the later. In either case, however, the more
conductive your cookware material, the better performance you'll realize
from any heat source. Don't think there can be much argument there...
--
Michael Harp
http://CopperPans.com

"Justin Won" wrote in message news:3tRbb.550068$Ho3.96040@sccrnsc03...
I want to buy a new drop-in cooktop. I am trying to get calibrated on the
relative BTU range.

I am considering a DCS cooktop whose center burner puts out 17500 BTU with
lowest simmer setting is around 1200 BTU (I got this number off a vendor,
the DCS website says 140 degrees at the lowest setting). The other option
is the Thermador with XLO. In this case, the hottest burner is 15000 BTU
but the XLO burners can go down to 200 BTU.

So my questions a

Will I notice the extra 2500 BTU (17.5k vs 15k) of the DCS (wok/stir fry,
boiling time)?
How are effective are simmer plates on a1200 BTU burner?
What is the effective low end BTU to simmer a sauce without burning or
boiling? I haven't seen many cooktops go below 850-950 BTU except for the
Thermador. Someone told me you can melt chocolate on a paper plate on the
XLO burner. Neat, but not that useful to me.

Thanks

Justin



(1)To return to the original post. My guess is that the 1,200 BTU
figure for the low end of the DCS is incorrect. A simmer at 140
degrees is pretty good, and I bet the low end BTU input rating to get
that simmer is well below 1,200. (The DCS site does not say; it just
reports the 140 degree figure.) So I would certainly not assume that
the Thermador simmer is better than the DCS on the basis of a supposed
1,200 vs. 200 BTU comparison.

(2)WindCrest (www.windcrestcnp.com) makes a 36" drop-in cooktop with a
dual center burner that is 18.5K BTU at the high end and 500 BTU at
the low end. In addition, there are two 15K burners, one 12K burner,
and one 9K burner. It is a bit of a drawback that the high BTU power
burner and the low simmer burner can't be used at the same time (as
they are the same dual burner, rather than separate burners). But
that might not be fatal for you -- and there are those 15K burners as
an alternative if needed. (WindCrest is a small company, based in
California, well known for high end range hoods; the cooktop is a
newer venture, but has generally been well received.)

(3) Wolf has a cooktop with simmer burners that go down to 300 BTU,
but the high end is only 12K BTU, which, for me, is not enough.


(4) Someone mentioned BlueStar (which I am strongly considering), but
that is not a drop-in cooktop of the sort you appear to want. Rather,
it is what generally is referred to as a rangetop -- basically, a
range without the oven. These sorts of "professional-type" units are
generally about 8" to 9" deep, with the knobs on the front (vertical
plane), and are much heavier than a drop-in cooktop. (BlueStar --
made by Prizer-Painter -- calls its unit a "cooktop," but that
terminology just confuses matters; it's what is more usually called a
rangetop, within the meaning I've just stated.) By the way, the
BlueStar supposedly simmers at 130 degrees, with the low end BTU on
that dual burner of 250; that futher suggests that the BTU figure for
the DCS is much less than 1,200.

(5) In addition to this forum, you might check out the appliance forum
at www.thathomesite.com; a wealth of informatino over there.

Good luck.