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Cooktop - BTU question
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 |
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Cooktop - BTU question
(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. |
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Cooktop - BTU question
>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 |
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Cooktop - BTU question
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. |
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Cooktop - BTU question
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 |
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Cooktop - BTU question
"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. |
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