(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.