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Boiler efficiency ? 's
Danscrew
Member Posts: 128
I have 3 Crest Lochinvar 3 million BTU Boilers in My Building that I work in.
My question is there is only one efficiency number related to this type of boiler ? One being how efficient the flame is burning. Which would give the most BTU's into the water? or am I missing something thanks Dan what would the formula be ?
My question is there is only one efficiency number related to this type of boiler ? One being how efficient the flame is burning. Which would give the most BTU's into the water? or am I missing something thanks Dan what would the formula be ?
0
Comments

The efficiency of a condensing boiler like the crest depends on the temperature of the returning water as well as the tuning of the boiler. What temp is the boiler running? Is outdoor reset setup? Has it be tuned lately using a combustion analyzer?"If you can't explain it simply, you don't understand it well enough"
Albert Einstein1 
The overall efficiency of a boiler  any boiler  is related to two main things: how well the burner is tuned and how clean the boiler is (it's also related, of course, to the boiler design  but there isn't much you can do about that). The efficiency calculated from the combustion measurements is a good approximation. If you have a way to measure the output power (BTUh) (which would be pounds of steam per hour at such and such a psi or gallons per minute of water at such and such a temperature rise across the boiler) you can divide that by the input power (BTUh  from gallons per hour of oil or LP or cubic feet per hour of gas) and get the overall efficiency that way.Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 
Guys thanks for your replies With that beings said one of the Boilers is running at 88%. on the combustion side that just means the flame and air settings are correct and the flame is giving off the most heat (BTU) correct?
And the flame is at its cleanest burn ? It doesn’t mean the boiler is running at that efficiency if your return water is above 130 degrees coming back to the boiler the Modulating condensing Boiler is running like a non condensing Boiler? So how much of an approximation is 88% combustion efficiency? I hope you understand my questions Thanks Dan0 
If you are really running at 88% you're doing about as well as you can expect with a regular boiler. If you are running a condensing boiler, and the return water is below 140, you can expect the overall efficiency to rise. This is reflected in the reduced temperature of the stack gas
It's perhaps a little complicated, but basically in combustion you get very hot gas as a result. This gas transfers its heat to the boiler and the water. That is referred to as sensible heat and is about 84 to 85% of the potential heating value of the fuel. However, that gas contains a good portion of water vapour, and if yo can condense that water vapour and recover that heat, which is referred to as latent heat, you can gain about 10% more total heat output  but that means that the stack gas has to be dropped well into the condensing range (below 140) and so almost always also means induced draught.Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 
efficiency is always a moving number. there are multiple factors involved in getting efficiency and according to testo different companies use different formulas. just like you will get a different efficiency number with a change in return water temperature you will also get a different number based on the temperature of the ambient air that its using. you get different numbers in the summer as you did in the winter. but its not by much.
when i perform pm's on my boilers, efficiency is the least of my concerns. its more about safety. always checking my co numbers. if i see that it's above 200 ppm that boiler is getting shutdown. no questions asked. i know asme says 400 ppm undiluted but a long time ago i saw in Massachusetts it was 200 ppm (i wished i save the article, but it was so long ago and i have never been able to find it again). plus i haven't seen any manufacturers spec designed for anything close 200 ppm.0 
Although it is an industry standard, combustion analyzer calculations, or the formulas used to calculate them have been mostly incorrect since their beginning. The actual efficiency of things is best described as bad goodbettermaximum.
A modulating boiler can be in the better to maximum range or the bad to good range. Most of them have very little adjustment, so hopefully the factory design is good.
The best indicator of efficiency is the O2 measurement. O2 determines how hot the flame is burning. If the O2 is 3% the flame is about 3100 degrees out of a possible 3600 degrees. If the O2 is 12% the flame is about 2000 degrees out of 3600 degrees. A combustion analyzer will calculate both as the same efficiency, maybe around 88% on a modulating boiler. and often the one at 12% O2 higher. The truth is that the one operating at 12% O2 is operating at 20% to 30% lower efficiency.
Fuel that is burning with less than 100 ppm of CO is burning at 99.9%. But before any of that heat is available to transfer the nitrogen in the air dilutes it down to the temperatures listed above. Temperature equates to btus available to transfer. 2000 degrees is not close to the same btus as 3100 degrees.
This might be a little more information for a consumer to know, but It just gives me a chance to add a little education to the industry which I have tried to do since 1985. Hopefully there will be more input on this!
6 
Thank you guys great info whos a good company in Brooklyn NY to properly Tune Three 3 million BTU Boilers ? thanks Dan0
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