combustion analysis

Matt_67

It will allow you to optimise combustion and thus optimise combustion efficiency. It is mandatory when natural gas is used. It is unfortunate that most oil service companies adjust combustion by lookling at the flame!

In my older house (1924), I managed to get a Viking c.i. hot water heating boiler at 82% combustion efficiency by having all the baffles in and adjusting combustion using a combustion test. My gas usage was actualy nearly half of my neighbours.

T. Riley

Professional combustion analysis question

If I hire a professional to take O2, CO2, and stack temperature readings with proper procedures and a recently calibrated digital instrument, what kind of accuracy can I expect in using these figures to determine the combustion efficiency of my steam boiler? I do not wish to address AFUE in this question.

Paul Fredricks_5

All you need to read the AFUE efficiency is stack temperature, and either O2 or CO2 (one is the inverse of the other). As long as the measuring instrument is calibrated correctly you should be accurate, + or - the design accuracy of the test equipment. As far as I know, AFUE is just the combustion efficiency, it doesn't matter if it's steam, hot water, or hot air.

I won't discuss AFUE vs system efficiency as requested.

Matt_67

AFUE

A combustion test will not give you afue: annual fuel usage efficiency. A combustion test will only give you combustion efficiency! A lab will do the afue, as one cannot take into consideration all the losses by radiation, standby etc....

Paul Fredricks_5

I thought AFUE was only the combustion part. A measure of how much heat is available for heating per unit of fuel, no matter how it's used. (I know, didn't want to get into this).

If AFUE is total efficiency, then testing stack and CO2 doesn't mean much.

Jim Davis_3

Bogus efficiency

Most combustion analyzers calculate and efficiency but this is rarely close to reality. AFUE merely takes the bogus Combustion efficiency reading and adds and subtracts points based on additional theoretical data.

There are certain target numbers that equipment should run which will determine how close they are running to the maximum efficiency that is possible. Oil equipment can run around 70% to 74% actual efficiency based on real numbers, but analyzers can calculated efficiencies as high as 86% which are impossible.

Brad White_185

AFUE versus Combustion Efficiency

Paul, there is a wide difference and it is common to confuse the two..

I have seen 100 year old boilers tested at the high 80's given as nearly complete combustion of gas as could happen in an old coal-fired chamber. The retention time in the chamber made for very high absorption into the gravity HW system it served, in one particular instance. (Economite stuck into an old H.B. Smith.... yes, I know...)

Before excess air was taken into account, the stack temperatures were in the 200 degree range and occasionally dropped into the 180 degree range at full fire, let alone at start-up. When she fired, she wrung out the heat from those flue gasses. No one was saying that it was wise to continue operation in this manner of course! This was years ago, more like 20, so I wish I knew then what I knew now to look for.

Naturally this did not (could not) take into account how over-sized the boiler was relative to the now-insulated church it served, the cycle times,(ramp-up/ramp down of high mass). The actual AFUE (pronounce Ah- Fooey! was likely in the 60's or less.

The key is "annual" and this takes so many other factors into account. Many of these factors we can argue are capricious, arbitrary and have nothing to do with actual operating conditions as Jim Davis pointed out.

Glen

I love this topic each time it pops up -

Accuracy of digital equipment is only as good as the tech calibrating it. Hows that for a vague answer. JD prefers the term bogus, while I prefer the notion of "variable". Each manufacturer will publish expected values, generally in terms of oxygen, or excess air, or even CO2. As combustion technicians we all have our "pet" setups based on one or more of these criteria. Efficiency is the last thing I look at - because as Brad mentioned - high % efficiency is not necessarily a good/safe thing. There are several good references to look at; Testo "Combustion Applications Guide, PN 400554 3200", the Bacharach website, and Firedragon has a great discussion on combustion in one of his books. I haven't read any of JD's info - but understand he has valid observations as well. Every major burner manufacturer has combustion expectations. And then there's the issue of type of heating appliance; as expectations change with each type and design. And finally - visit Robert Bean's website for an education on comfort.

Paul Fredricks_5

Ya know...

... I always thought AFUE was combustion efficiency, and system efficiency was something else. I just pulled out my old Fire Efficiency Finder from my old wet kit, and sure enough it says combustion efficiency. Still so many little holes in my knowledge, just call me swiss cheese.

Jim Davis

90% percent of that efficiency finder could be cut off because it is useless. The rest would make a nice book mark or fire starter.

Paul Fredricks_5

I have it nailed to the wall. No, not this Wall.

GW

rock on Jim

Heat guys, stick a dozen candles in your boiler and check efficiency. Pretty efficient huh?

lets call this subject "Reality Combustion"

If anyone wants to have their old ways put to bed and get a real life dose of Reality Combustion, check out Jim Davis.

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GW

Smart People (edit)

I have a sister in law who's married to a professor in Physics,,, actually the sister is law is a professor in electrical engineering, I have a father in law who's a professor in civil engineering, I've brought up the subject of combustion to all three of these smart people and I can't seem to find an answer on complete combustion.

Jim, that leaves you, you're the man. Do you have real life charts?

My wife is the odd duck of the family; she's the psychologist.

Gary


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Darin Cook_5

Hey Jim

How have you been Bud? Are you going to be in the Northeast any time soon? I think it is time for a combustion refresher, plus it is your turn to buy!







Darin

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Jim Davis

Long time Darin. Would be great to see you. Haven't looked at the schedule for April and May but might be back in the area. Got Philly, Louisville, Vegas coming up next. Hey come to Vegas where it is warm.

Bob Sweet

Hey Jim

what dates are you scheduled for Vegas??

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Jim Davis

April 8,9 & 10