\"Boiler Eficiency\"

Maine doug_15

Could we have a discussion about boiler efficiency? When the boiler is serviced and the measurements are done and the pronouncement made, "It is running at XX percent efficiency", what does that mean?

How does boiler sizing (over-under) affect this "efficiencey" in a given structure?

Does the quality of the fuel have an impact?
Does this "efficiency" start to decrease immediatly after the servicing as winter progresses?

As it gets colder outside, what happens to this number?

If my boiler is at 85% and your boiler is at 85%, is this the same even though one boiler is larger than the other?

If I have a really old monster that the tech says is running at 85%, is this the same as a new boiler running at 85%?

Will a given boiler produce different amounts of heat but still be at the same efficiency?


What are the variables that create this efficiency number? (maybe this should be the first question)

I am sure there are more questions but this is what I have at the moment.

Doug

Andrew Hagen (ALH)

Efficiency

There are different kinds of efficiency. Combustion efficiency is a measure of how much of the heat content of the fuel stays in the boiler while firing. There is only so much efficiency to be had from a cast iron, non-condensing boiler. This generally peaks in the high 80's due to their inability to recover the heat contained in the water vapor in the exhaust.

This is only the beginning when it comes to system efficiency. Modulating, condensing boilers have the additional benefit of only firing to the fluid temperature the structure and heat emitters require. With a traditional boiler you get full output or nothing. This increases standby losses, increases cycling of the boiler, and can cause the system to require controls to take the hot boiler water and temper it for radiant panel use.

When you burn more fuel, higher conbustion efficiencies benefit you more. This is why I think high heat demand systems such as snowmelting systems, or even large homes, should always be fired by condensing boilers. When a home is smaller, say 1500sf, the individual benefit to the homeowner is much less significant. Though collectively, if we all had condensing equipment we could really put a dent in our fuel consumption.

-Andrew

Tony Conner

Unless...

... you've got the instrumentation in place to measure the net heat out of a boiler (either steam or hot water), and a dedicated fuel input meter, nobody can calculate boiler efficiecy.

There are typically 3 kinds of eff for boilers (and this can be applied to forced air units or gas fired unit heaters as well).

1/ AFUE which is very much like the fuel economy ratings that manufacturers assign their new vehicles, based on a standardized set of lab tests. As with cars, I don't think it necessarily reflects much in the way of useful info. It sure doesn't reflect actual eff.

2/ Combustion eff - which while important, isn't the same as boiler eff.

3/ Boiler eff - this is the big picture, and captures all of the losses, including combustion. It doesn't however, tell you where the losses are. You can even have a boiler using substantially more fuel to heat the same house, but still have the same boiler eff (and also combustion eff). If there are leaks in the system - condensate not getting back in a steam system, or water having to be constantly made-up in a hot water system - the boiler now has to heat the cold make up water back to system temp. This will, of course, require more fuel. However, since proper boiler eff is calculated off NET heat out of the boiler, the fact that the boiler is adding much more heat to each lb of water means that this balances with the increased fuel input to give you the same eff. In this case, the problem is NOT at the boiler, but out in the system. Fix the leaks, the cold make-up water stops being fed into the boiler, and the fuel bills drop. But the boiler eff remains unchanged.

Tony Conner

Unless...

... you've got the instrumentation in place to measure the net heat out of a boiler (either steam or hot water), and a dedicated fuel input meter, nobody can calculate boiler efficiency.

There are typically 3 kinds of eff for boilers (and this can be applied to forced air units or gas fired unit heaters as well).

1/ AFUE which is very much like the fuel economy ratings that manufacturers assign their new vehicles, based on a standardized set of lab tests. As with cars, I don't think it necessarily reflects much in the way of useful info. It sure doesn't reflect actual eff.

2/ Combustion eff - which while important, isn't the same as boiler eff. It's the eff of the burner.

3/ Boiler eff - this is the big picture, and captures all of the losses, including combustion. It doesn't however, tell you where the losses are. You can even have a boiler using substantially more fuel to heat the same house, but still have the same boiler eff (and also combustion eff). If there are leaks in the system - condensate not getting back in a steam system, or water having to be constantly made-up in a hot water system - the boiler now has to heat the cold make up water back to system temp. This will, of course, require more fuel. However, since proper boiler eff is calculated off NET heat out of the boiler, the fact that the boiler is adding much more heat to each lb of water means that this balances with the increased fuel input to give you the same eff. In this case, the problem is NOT at the boiler, but out in the system. Fix the leaks, the cold make-up water stops being fed into the boiler, and the fuel bills drop. But the actual boiler eff remains unchanged - the system eff has improved.

Maine doug_15

Hmmmm

So combustion efficiency is the number we get from the tests after service and boiler efficiency is not something we can easily measure in the building. And the third piece is system efficiency which includes the house, the emmiters, conduits from boiler to emmiters (pipe and duct?), design factors like balance and controls and use variables.
Thus one should not place too much value in this combustion efficiency number?

Tony Conner_2

It's...

... a very important number, and represents a good chunk of boiler efficiency. The combustion eff % is usually somewhat higher than the boiler eff. It's only PART of boiler eff. It's entirely possible to have a really great burner, all dialed-in, mounted in a boiler that's a piece of junk, as far as heat exchange goes, or all scaled-up. When you get right down to it, all a boiler (or furnace) really is, is a heat exchanger. And like everything else, some are awesome HXs, and some are not.

RoosterBoy

in a way it is a bad joke Foysted on the public *~/:)

i have a slightly diffrent interpretation of AFUE.

be that as it may...what you are asking is areally good question. What you might be better served by is how effective is my mechanical system. perhaps as a lead in the description given by Tony Conner would be the place to start.

i contend that the battel of the modern home owner to heat the planet with thier individual fuel consuming mechanical system of thier choise is a battel not soon won. did you see a post of mine a year or so back with a boiler inside on the gravel snow and ice cranking away to heat the home on a - 30 day ? well,we were'nt winning the battel by a long shot. that is an example of what i mean. the entire building envelope and its fuel useage And the btu's that actually remain within it and are doing something to ameliorate the environment vs a piece by piece description of the heating system would be more in order when disscussing effectiveness of the mechanical system.

i would like to chirp up The Bean for a momment,please to take a look at his site...Healthyheating .com not that you dont deserve a better answer to your question just that it might more clearly depict another view point on the subject.

*~/:)

Maine doug_15

The Bean Site

I see I have a lot of reading to do. Thanks for the pointer.

doug

Tundra

I like to describe boiler efficiency as being similar to trying to come up with $1.00. You mihgt find a quarter here, a penny there, and a nickle somewhere else. You are never going to come up with the entire dollar but everything you do will help. A short list of things to consider: cold start boilers, outside air, cooler boiler temp. (requires more radiation), direct venting, higher combustion efficiencies. I am sure that many here will have additions to the list. Remember to look at the heating system as a "system" not just a boiler with stuff attached.

Jim Davis_3

Combustion Efficiency

Good to see there are finally some that are understanding that Combustion Efficiency doesn't really tell the real story. Combustion Efficiency calculations are based on one BTU value of the fuel. Recent articles in GAMA have stated that the BTU's in fuel are not constant. Beyond this the actual usable BTU's that we can create from any fuel are 5%-10% less than the fuel is actually rated. 90% of all calculated combustion efficiencies on most analyzers are either mechanical impossiblilities or unsafe conditions. The remaining 10% can be off more than 15%. AFUE merely takes these readings and calculate some additional theoretical values that give even more misinformation. I was reading a boiler spec sheet last week that said the boiler had a AFUE of 92% but it had an input of 100,000 and an output of 79,000 on the same spec. Oxygen, Flue Temperature and CO plus Smoke on oil are very important measurements that must be taken. All other calculations on an analyzers are fabricated based on theoretical data in a perfect world. Jacket losses only occur on equipment installed outside the heated space otherwise it is still heating the space. Extra points for minority owned companies? Thermal is measured efficiency, GPM X 8.33 X 60 X Delta T equals BTU's. Combustion analyzers cannot calculate these numbers even close most of the time.

George_10

A cleaned and treated system will

maintain what ever boiler efficiency the system is capable of as it will keep the HX free from corrosion and scale. These two heat thieves are best kept at bay from the HX.

It takes very little build up on the HX to raise the fuel expense significantly.

So there are two very good reasons to clean and treat systems. Reduce breakdowns or repairs and to save on the energy bill.

hydronicsmike

Well....short answer out of lack of time at the moment...

...run the boiler at the lowest possible water temperature at all times while protecting it from condensation (if it is a non-condensing heat source) and while minimizing boiler short cycling.

The longer the boiler cycle and the lowest supply temp possible results in the highest efficiency possible.

Running the boiler at 180F, usually isnt the time the boiler is most efficient.

Surprise (otherwise I wouldn't bring it up ): Look at tekmar tN4 and learn about Zone Load Synchronization. Its the answer you are looking for. At least next best thing to NOT oversizing the boiler.

Mike

hydronicsmike

Ok...I got another minute....

...Zone Synchronization and Minimizing Boiler Short Cycling with tN4:

Boiler Short Cycling has been minimized with tekmar Controls effectively as a standard feature since 1995 (since 370 and 371 series of Controls). The Controls minimize the short cycling by automatically adjusting the boiler differential based on load response. This is done by the control monitoring the boiler supply sensor every time a boiler fires. If the temperature increases slowly, then the control knows that the load must be high as all the BTUhs the boiler produces are being put into a system or a load. Since it will take a fair bit of time to get to the target temperature, short cycling should not be a question and the differential the control calculates will most likely be small.

Alternatively, If the temperature increases fast, then the control knows that the load must be rather small as not all the BTUhs the boiler produces are being put and used by the system or a load. Since it generally requires a very short period of time to get to the target water temperature, short cycling willbe an issue and the differential the control calculates will most likely be bigger. As a standard, the differential can vary from 2 to 42F.

Lets keep this clear, though. It will not be able to eliminate short cycling if the boiler is grossly oversized (which sadly, lots of them are), but it will do the best it can and the best you're going to get without replacing the boiler with one that it properly sized.


Zone Load Coordination: is another brilliant feature. In tN4, since all zones are communicating, the system control knows how much heat and when it is required for every zone. So instead of letting all zones come on at random times like a tytpical thermostat system does (also making it hard for any controller to operate a heat source properly without being able to anticipate any load changes), it operates a heating system zone by zone on a cycle length. Within a cycle, the control actually communicates and demands/instructs all zones to come on at the beginning of a cycle which in turn maximizes the load on a heat source for as long as it can based on loads in the different zones and minimizes short cycling. It would never starve the heat source from too high of a demand, as even if a boiler is sized right( which again, unfortunately I dont see often enough)it is capable of providing enough heat during a design day.

I hope this all makes sense. If not, please call me at the office at any time when I get back after October 16th and I would like to chat with you about it more if I may. Its not a sales pitch...it's a fact. We simply try to build what the market needs and many of you great supporters demand!!

tN4 doesn't only have many of the features you been waiting for, but also when you look at the prices, it is more affordable than ever to have a quality control solution that saves you money!! Fuel is getting more and more expensive and you can be making many of your customers happier.

Only a happy customer is a good customer, guys!!


If you care to find out more about it sooner, call my friends and colleagues Paul Williamson or Michael VanDerHoek at 250-545-7749.

Best Regards from the UK.....where is Gary????

Mike