OK, Boiler Manufacturers...

Tony Conner

...I've moved the string "Energy Assumed Vs Energy Produced" back to the top. What, exactly, is it that you base your published efficiencies on? Is it COMBUSTION efficiency, or is it BOILER efficiency?

Mark Hunt

Good question


The Munchkin literature lists a 92% A.F.U.E and a 96% combustion efficiency.

I'd like to hear what the numbers are based on as well.

Mark H

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kf_2

AFUE

Guys,

AFUE efficiencies are only tested on residential boilers less than 300,000 BTU/hr, and are NOT tested by the boiler manufacturers. There is a detailed procedure in ASHRAE Standars 103 that explains exactly how AFUE numbers are derived. It is basically 140 degree supply and 120 degree return under a CONSTANT load.

As far as comb. eff vs. boiler eff. Doesn't combustion efficiency have alot to do with stack temperatures. If so, doesn't this mean the stack temps are lower because more heat is being transfered into the water.

By the way, I believe that the Federal Trade Commision states that any boiler with a listed AFUE rating shall not publish any other ratings but the AFUE, to the public. Unfortuneatley, this is not enforced so the Munchkins of the world remain free to CONFUSE the buyer.



kf

Michael B

speaking of confusing

how can we have a standard AFUE test based on a 140 degree supply 120 return when a "typical" cast iron sectional boiler can not take this kind of cold temp. over an extended period of time? Shouldn't a test reflect the reality of the product?

Michael Bleier
Able Distributors
"The Supplier Who Works With You"

Eric Taylor_20

Read carefully

I just found this:

http://fire.nist.gov/bfrlpubs/build95/PDF/b95077.pdf

Posted it in the other thread just now. I need to read it some more, but there are cyclic as well as steady state measurements rolled into the AFUE. You have to wade through the details but its all there.

Eric

Eric Taylor_20

Your mileage may vary....

Boilerpro_2

Mike

According to a source at Dunkirk, the minimum return tmpe to thier cast iron boilers is about 117F. This is somethng that is very confusing. Always hear about the need to keep a boiler above 140F, but where is this measurement taken...supply water, return water, average water temp, or on the flame side of the castings. I believe it is the last because I have several boilers running at about 140F supply, 120 F return with no condensation. Remember when the burner is on, the flame side of the casting is warmer than the water side and the thicker the casting the greater the temperature difference.



Boilerpro

Tony Conner

The Stack Temp...

...can be influenced by a number of factors. Scale on the water side, and/or soot on the fireside of the heat exchanger that is the boiler will show up as increased stack temps.

If everybody had to take the actual boiler efficiency calculation as what was published, then that would be an absolute apples to apples comparison of the whole box.

It may help to think of boiler eff as an overview of the performance of the whole boiler. Take, for example, that you've got ten cubic feet of natural gas being supplied to a burner over an hour. Assume that each cubic foot of gas as 1,000 BTU if it is burned under ideal conditions (100% burner eff). This means that you've bought, and supplied to the burner, potentially 10,000 BTU. Now, on the other side of the hot water boiler, there's a pump circulating 0.61 GPM. You know this because you've got a flow meter in the piping. The delta-T across the boiler is 20 *F. You've installed thermometers, and you can see it. You're not guessing, or assuming anything about either the water flow, or the delta-T.

0.61 GPM X 500 X 20 = 6,100 BTU/hr

This is how much heat is being supplied to the structure, by the boiler.

You've also taken the gas meter readings, so you know that you've put 10 cubic feet of gas into this boiler over the same time period.

(6,100 BTU/hr / 10,000 BTU/hr) x 100 = 61% boiler eff.

We didn't look directly at combustion efficiency for this calculation, but it WAS in there, as part of the package. So was the effectiveness of the heat exchanger, and any skin losses, and everything else that is classified as a loss. The boiler eff calc just tells you WHAT the losses are, not WHERE they are. Now, you have a starting point. If you know that the manufacturer says that you can get just over 64% boiler eff under whatever the standard conditions are, you're missing 3%. Time to track that down. Any fouling on the water side? Nope. Not likely any on the fireside, with gas, but check anyway. No hot spots on the casing - that seems fine. No heat leaking out of there. Let's check the burner! Things are a little off. So adjustments are made, based on the instruments that a lot of you guys carry. Excellent! We do the meter reading thing again, and notice that the water side conditions are identical to the first time. But the gas comsumption has dropped to 9.5 cubic feet for the same time period - one hour. We'll do the math again:

9.5 X 1,000 = 9,500 BTU/hr supplied to the burner

0.61 X 500 X 20 + 6,100 BTU/hr output.

(6,100 / 9,500) X 100 = 64.2%

You found the missing boiler efficiency!

Now you've hit the mark set by the manufacturer.

But suppose the first set of numbers existed, but when you checked the burner, it was right on. No improvement to be had there. But the stack temp was running higher than normal. You checked the water side of the boiler, and found it scaled-up. You get that scale cleaned off of there, and run the test again. Remember, you haven't TOUCHED the burner. But you still see the same drop in fuel use, down to 9.5 cubic feet per hour.

You've hit the same boiler eff improvement without any burner adjustments at all. The problem laid totally with the heat exchanger that is the boiler proper.

Combustion efficiency is a very important thing - but it's not EVERYTHING. Comparing boilers on the basis of combustion efficiency alone, is like comparing apples to anvils.

Mike Kusiak

AFUE testing

I did a little searching, and found the DOE regulations for testing AFUE. Their tests are almost completely based on the ASHRAE 103 Standard. Although not all the info is there, I was able to get some details.

As far as I can tell, the AFUE is based on an analysis of flue gas to determine steady state efficiency, so it is basically combustion efficiency test. The boiler is operated at rated input, and the input BTUs are calculated from the gas flow rate and the higher heating value of the gas used. Water is circulated through the boiler at 140 F out, 120 F return, plus or minus a few degrees. There is no mention of measuring the water flow rate, only that you want to maintain the 20 F delta T. Thermocouples are placed in the flue pipe to measure gas temp, and flue gas mass flow rate and CO2 are measured. These measurements are plugged into a complex formula to determine heat loss up the vent pipe, and the heat loss up the vent is calculated. The flue heat loss is subtracted from the BTUs in to give the output of the boiler. There is no mention of actually measuring the flow rate of the boiler water and delta T, and calculating how much heat gets to the water. I appears that AFUE considers anything that doesnt go up the flue useful output, jacket losses included.

This is a simplification because many other factors are taken into consideration, cycling, standby heat loss, pilot energy use, etc, The formulas for calculation are complicated, and many assumptions are made.

All in all, It appears that AFUE is basically a combustion efficiency test, not a boiler efficiency test, and therefore doesnt necessarily compare to what you will get from water delta T times flow rate.

Tony Conner

Thanks For...

...checking that. They've essentially developed a test that is so complex that it doesn't translate into anything meaningful in the real world.

And the real test is SO SIMPLE to run. A fuel meter, that you have ANYWAY, and themometers, that you have ANYWAY. The only thing that doesn't normally get installed is a WATER METER. If only somebody would invent a WATER METER, this test could actually be run in the field by normal people. Or in a lab, to provide some kind of meaningful information. Oh wait...I think I've found about a million kinds of water meters, y'know, already on the market. Gee, maybe somebody should tell the guys back in the lab that they don't need a dozen supercomputers, 50 zillion dollars in instrumentation, and a staff of hundreds. They could have a guy just drive over to a plumbing wholesalers or industrial supply house, and buy a freakin' water meter for what? $100 tops? Hey, go all the way and get a good industrial grade meter for the lab - maybe a grand.

As far as I can tell, NO manufacturer has responded to my question regarding combustion vs boiler eff. The silence is deafening, and says far more than I ever could.

steve_6

boiler manufacturers

Why are you not answering?? We want to know, you know , inquiring minds!!!

Tony Conner

I Was...

...probably being a little unfair to the guys in the labs in my earlier post. I'll bet THEY know what's right, and what's being printed in the glossy literature isn't QUITE the same thing as things under test have shown. The engineering people know, too. But if ANYBODY says anything, they'll be drawn and quartered by the MBAs and marketing people who run the companies.

I think the published numbers are not "incorrect". But they offer a very one-dimensional view of boiler performance, and I urge that anybody who's trying to make an informed decision by referring to those numbers, to ask a LOT of questions about just how those (or ANY) numbers came to be.

Remember, figures don't lie - but liars can figure.

Unknown

Steve

That is because it WAY too complex to answer in standard laymen's terms. The AFUE testing is done by the ASHRAE Standard and it is indeed very complex. But it as also very reasonable. I downloaded the standard last year and attempted to make heads or tails of it. Our folks in Research and Development are very well up on it, but even they have had difficulty trying to explain it to me in a few words or less. It is based on many, many test factors with varying water temperatures, cycles and other factors. When I attempt to describe AFUE, I basically state that is based on the way that the boiler is able to handle what it happens to be connected to. Take for instance our Revolution boiler. It incorporates a bypass with a variable speed injection system to keep the boiler safe from condensing and possible thermal shock. This pumping system really has nothing to do with combustion, but by using it, we are able to keep the boiler from condensing with return water temperatures as low as 55°F. This boiler has an AFUE of about 88% because of the way it can handle the system water temperature. The same goes for our Opus O-1 oil-fired boiler. This has the same piping setup as the Revolution and has turned AFUE results of almost 90%. Combustion efficiency of this, however, is about mid to low 80% range. I hope this helps you to understand this a bit more. Don't ask me for a complete explanation as i will not be able to give it to you. This is more than likely why you have not heard from any manufacturers. All I can say is to "Trust the Results" and not to try and reinvent the wheel. It is way too complex, but it works.

Glenn Stanton

Manager of Training

Burnham Corp.

Tony Conner

It's Really Great....

...that you responded. Points to both you and Burnham.

But I REALLY hate it when folks get told "We'll, we'd explain it to you, but...it's just WAY to complex."

It really appears to BE that complex, the way it sits now. And I think it's being spun into things that it's NOT. Boiler eff calcs have been around since the horse and buggy days. With some basic (and I DO mean basic) math skills at all, anybody can figure out boiler eff out on the back of an envelope with a pencil. It's not much harder to do than figuring the gas mileage on your car.

Keep the existing test, if it's necessary. But give ordinary people information that they can use. Things that are unnecessarily complex have the capability of being spun into things that they are NOT. Like combustion eff being confused with boiler eff. And if the boiler manufacturers didn't actually TELL people that these are not the same, they have allowed (and continue to allow) the misconception to exist.

Mike Kusiak

Tony, I think what we want to know is what the DOE calls "RE", which is the percentage of the input energy actually transferred to the boiler water. I found this term in the latest DOE standard for domestic water heaters. According to what I read, the RE of present water heaters is about 76%, and the new standard proposes raising it to 78%. It is interesting to note that you see energy factor "EF" ratings for water heaters all the time, but you have to go to the technical standards to see the actual thermal efficiency stated. It would be nice to have all the info, but I guess the DOE doesnt want you to have all the information, as you might be "confused".

Tony Conner

I Think...

...that many organizations, and HUGE numbers of people have gotten hooked on software, PLCs, digital readouts, printed circuits and spreadsheets. There are many engineers who, if they see some calculation not done with latest version of the software, doubt it's validity. This, of course, is nonsense. All the software does for you is the math. In most cases, the formulas involved are 50 to 100 years old, or more. If you don't have a solid understanding of what you're doing, all the software, spreadsheets and printouts in the world won't help you. They will, however, allow you to overcomplicate things, and confuse a lot of people.

The way this situation looks to me (and I don't buy, sell, install, or service residential boilers - so I have no axe to grind) is that the process to calculate "efficiency" numbers required by government agencies, and supplied by manufacturers are so complex as to be pretty much useless to the average contractor, and the end customer - the homeowner, who live out here in the real world. All the existing process seems to have done (if the recent discussions here are any indication) is to totally, completely confuse almost EVERYBODY about just what the published efficiency numbers represent. I think this is terrible, and 180* from what these values are supposed to do - HELP PEOPLE MAKE INFORMED DECISIONS.

If proper boiler efficiency numbers were required to be stamped on the boilers and printed in the literature, there wouldn't have been much of a discussion about Munchkin Vs Viessmann and the economics involved in retrofitting that house. Comfort is hard to define as it varies from person to person. But boiler efficiency? That's a cold, hard MEANINGFUL number that is simple to generate accurately, and easy to understand by almost anyone. And that's a fact.

Mark A. Custis

Now you guys did it

Jim Davis dropped a how much gas is there in Oil and how much. if any, wood would a wood chuck chuck if a woodchuck (we call them groung hogs in OHIO, tasty) could chuck etc.

The real question seems to me is, "How much is it going to cost to heat my home?" or "What do I have to spend to FEEL COMFORTABLE?".

Glenn hit it on the head, who cares what the AFUE means.

I returned to college to take up an ME/PE degree so I could charge enough teaching this stuff to make a living, and when I brought home a rudimentary algebra book, my then fifth grader, translated what looked to me like chinese. I strive to use all that is available me to answer the real questions and know MEs and PEs who still talk to me.

SO! Good luck with your quest, and I will keep answering I don't know, when asked about energy cost and zero in on you will feel comfortable at the lowest possible cost.

Your milage may very, batteries not included.

Mark

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Mark Hunt

Mark


Would you deny us our quest??

I agree 100% that AFUE is really not important. I am just curious as to how it is that all these boilers get lumped into the same category.

I have my preferences when it come to equipment, and I can not believe that "all boilers are created equal" when it comes to "efficiency".

Is the AFUE supposed to make a level playing field?

It would seem to me that the AFUE numbers would only confuse the issue as currently listed. Boiler A is no different than boiler B even though boiler A has this, this, and that.

Drives me nuts!!

Mark H

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Unknown

Mark, Tony and others

It isn't necessarily the boiler manufacturers determination what the AFUE efficiency ends up becoming. These guidelines are drawn out for us to abide by when certifying and having our equipment catagorized and tested. Boilers do vary in the way they handle a similar system setup or task. That is exactly what AFUE means. The way the boiler performs in any given condition. In addition to this, considerations have to be made as to which catagory the boiler is actually in. But the consistancy of the guidelines for this testing is what makes it realistic and fair to us, the installer and the end user. There has to be a common standard or outragous claims of efficiency would be the end result. Hope this helps.

Glenn Stanton

Tony Conner

I Realize That...

...the current method of testing does represent a common standard. And I also fully recognize that there MUST be a common, verifiable way to determine efficiency.

However, I have come to believe, based on numerous postings here over the past while, that the main flaws in the current method of testing and rating, are it's unbelievable complexity, and the confusion that the final number produced generates - even among very competent and experienced contractors.

I KNOW how to calculate boiler efficiency, because I did it for years as a chief engineer in industrial powerhouses. I also know what a lot of people on this board THINK they know boiler eff is, based on published data. They are mistaken. The numbers they are being shown (abeit by regulation) are NOT boiler efficiencies. Even I'm not sure what they are, because - nobody can effectively explain the process that generates them. And this concerns me greatly. Every time I hear "...well, we'd explain it, but you wouldn't really understand - it's a VERY complex procedure", alarm bells go off in my head. I'm not suggesting for a moment that you fall into this catagory - but many guys, with a certain "moral flexibility" LOVE situations like this. Everything is so complicated, that NOBODY understands what's going on.

That's why I just LOVE the good old-fashioned, simple, effecive, accurate, and highly understandable boiler efficiency calculation. Very little chance of drifting into "spreadsheet madness" with only 2 values - heat in, and heat out. Keep the AFUE measurement, emission reporting requirements, combustion efficiency tests, etc that are required either by gov't regulation, or your internal company requirements, but I would urge all those involved in determining just WHAT is reported, and HOW it is determined, to look at the kinds of postings that have gone on here. A lot of the contractors who post here represent the the best there is out there. And THEY don't understand what your numbers mean. In the last plant I ran, the LITTLE boilers had an input of about 50 million BTU/hr each. And I don't understand what your published numbers mean, and NOBODY can effectively explain it, or WHERE those numbers came from.

Thanks for your input on my question, but I'm literally just sitting here, shaking my head. This is a pretty sorry state of affairs.

Tony Conner

The Scorched Air Guys Shouldn't...

...be rejoicing about this exchange, if they are. THEIR stuff can be tested in EXACTLY the same way as a steam or hot water boiler. You just need an air flow measurement across the building heating side of the heat exchanger in the furnace, along with the inlet & outlet air temps. Water heaters can be done using the same method. If they were going to be used for a building heating application, the inlet/outlet water temps for any standard eff tests would have to reflect that.

Contractors and end users could sit down, and make a real, apples to apples comparison regarding a set of efficiency values that are ALL determined in exactly the same way, and feel comfortable that the process that generated those numbers is transparent, and understandable by normal humans.

[Deleted User]

However...

I hear the frustration in your voice Tony, and I concur to a point.

You are used to seeing equipment on the industrial side of the fence where the equipment is being run 24-7-365. And in your case, the rating system you propose makes ALL the sense in the world. No stand by time, hence no need to concern yourself with standby losses.

The reality of the fact is that most residential systems spend 98% of their time in standy by conditions, which means that you could have a real high number as it related to overall instantaneous production, but terrible numbers as it pertains to standy conditions. (i.e. water cooled exterior jacket, no insulation)

That said, I agree with you that there does need to be a methodology of looking at the equipments net hourly thermal efficiency at a full all out burn with a maximum recommended load. It would help people in your posisiton do a better job of specifying thermally efficient equipment. But then again, unless you are dealing in a perfect world, you too are subject to part load considerations, so it makes sense to also show net thermal capacity at part load considerations. If your burner maker has a good handle on air to fuel flow control and can guarantee an extremely good burn through the burners full range, then it shouldn't make a big difference in the final numbers.

Anyway, I wouldn't hold your breath waiting for the few boiler manufacturers who hang out here to jump up on the pulpit with answers to your question. I honestly don't think they want to publish the numbers for fear that it would confuse the buying public. They already have a means of comparison, it's called AFUE, and that's all they think the buying public needs to know.

You and I know the difference, and we also have the technology to test their appliances and that's the most important thing.

ME

Tony Conner

I Really Don't...

...see generating boiler/furnace/water heater-as-space-heater eff numbers as a problem. To me, cycling vs steady state operation is the same as the fuel economy/mileage data required from the auto makers for highway and stop & go driving. Why not two eff values - one steady state and the other cycling? If there was one for cycling, then manufacturers with better control over heat losses up the stack when the unit is down would get some visible credit for it. They'd be clear-cut, representative numbers that can be used for meaningful comparison, and you don't have to be Steven Hawking to understand how the numbers were generated. And it would be pretty simple for purchasers to do a little cost/benefit figuring - "what do I get for what I pay?" kinda stuff. It would really help cut to the chase for discussions like the Viessmann Vs Munchkin string.

And, I see all kinds industrial steam boilers with burners & controls that are utter crapulance. They yo-yo on and off every few minutes on nights and weekends. The heat being blown up the stack every time these things go into post purge and pre purge must be just spectacular. And that would be on top of the standby losses. "Low bid" is very much alive and well in industry. And the stuff that happens with compressed air is even worse.