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