How efficient is my boiler? No really

hot_rod

So a number of formulas to use to get to efficiency, steady state, the condition where boilers are rated.

Cycle efficiency as boilers do not always, probably seldomly run at steady state.

Run cycle, how many and how long the boiler cycles.

Numbers are probably close to what you see in of oversized boiler installations. Maybe 80% of residential fixed output boilers??

If you have equipment to collect some date, enter your own numbers.
Thanks to Siggy for the formulas and number crunching.

First slide shows cycle efficiency using different boiler rating numbers. Shows run fraction with a 10 minute run time. To the right a 60K load on a 100K boiler at a 40 day. Design of 70°inside 0° outdoor. 15,000 Btu/hr. internal gains, 4.8 KW.

The second slide shows a 150K boiler on a design load 100K application.
20,000 btu/hr. internal gains is everything inside the home adding heat, people appliances, lights, computers, so about 6KW.
A fixed output boiler in a zoned application will see these operating conditions, run fraction for example.

ChrisJ

I don't know....
I think compared to my ICE car and wife's minivan my 83% steam boiler is likely doing very well in regards to efficiency.

RayWohlfarth

@Hotrod Thats fascinating. So at 40 degrees outside temperature, it only operates at 15% of the time. That makes sense. I guess the key to better efficiency is to increase run time. @DanHolohan idea of installing a time delay relay on the burner to delay ignition while the circulator is pulling heat from the boiler will do that. It seems you could do that with all the outside temperatures in a heating season. I use the bin temperatures to calculate the consumption when Im doing a comparison.

HomerJSmith

I had a conventional cast iron boiler and in winter months my gas bill was around $300 and I put a mod/con in and my gas bill went to about $150. It was 92% efficient rated boiler supplanting a 82% efficient boiler.

I don't much care about the boiler rating. I care about the money I save. I leave the efficiency to the lab experts. I attribute the saving to the modulation and the outdoor reset features. God bless those engineers.
Now if they can only design a mod/con that last 40 yrs, but that would probably hurt their bottom line.

fentonc

I've tried quantifying this for my very-oversized CI boiler. The data is based on tracking firing time of the boiler vs an estimate of heat output based on sampling the supply and return temperatures for each zone every second, using interpolation to get the BTU output for each zone at that average temp, and then integrating it over time. The measured results agree pretty closely with those charts:

fentonc

Currently averaging 48.71% efficiency over the last 112 days

pecmsg

Get someone out with a combustion analyzer and they’ll tell you. 

Steamhead

RayWohlfarth said:

I guess the key to better efficiency is to increase run time. @DanHolohan idea of installing a time delay relay on the burner to delay ignition while the circulator is pulling heat from the boiler will do that.

Current models of both the Beckett AquaSmart and the Hydrolevel Hydrostat can do this. You need to turn the option on in the setup program, but that's not difficult.

hot_rod

Anything to increase run time will help. Timing out the burner ignition is one trick, as long as on design day, a properly sized boiler can run, burner on, as long as it needs to cover the load.

hot_rod

Anyone have some actual mod con run data to plug into the formula? Unless there is a lot of run time below the lowest turndown, it could run mid to high 80%, even out of condensing mode, 180 swt.
Days spent at condensing conditions into the 90%. So even on zoned, high SWT systems, 50, 60, 70% or more in condensing mode? Quite possible. BIN data like Ray showed would tell the story.

JakeCK

Why I have wanted to add a large buffer tank to my boiler for years now. 

Edit: Today it has been hovering around 35f, I've been seeing run times of about 18 minutes or so, and a off time of about 70 minutes give or take a few minutes. Interestingly the on time doesn't seem to change much regardless of outside conditions, it is the off time that changes in response to outside temperature. I suspect this is because of the large mass of my old converted gravity system. It just takes a lot of energy to spin up that flywheel, and once it's spinning it takes a while to spin back down.

Boiler is 140k btuh input, 115k btuh output. Steady state is calculated around 80% both by the boiler plate and by combustion analysis. Calculated load is right around 60k btuh at a design of 7f.

Hot_water_fan

Good thread! For about 1000 days with >0 HDD65, I can plot average gas input / HDD 65. If I estimate max efficiency is nameplate 82% and that occurs at the lowest BTUs/HDD65 (38.7kbtu/HDD 65), then I can then divide .82*38,747 BTU/HDD65 by the average BTU/HDD65 for every other HDD bin, which gets a similar relationship to the others posted above. However, the boiler is way oversized, I think it's unlikely it ever gets up to 82%. If 82% is the best case and that corresponds to 38,747 btu/HDD65, I've got a seasonal efficiency in the 60% range.

EricPeterson

What about simply lowering the boiler setpoint so that the run cycle is longer?
Wait a minute - that's outdoor reset - maybe it's time for me to install that option on my ES2.
But it's $430.32 from SupplyHouse, I would like to first know the payback period be for this.
Based on my fuel cost of $1,484.36 for last year, and an estimated savings of 15% to 20% from US Boiler, the payback period would be a couple years.
So it's probably worth it?

Eric Peterson

EBEBRATT-Ed

before I sold my house I had an oversized gas fired atmospheric boiler. 100,000 input with a 50,000 load.

I put a strap on reverse acting aquastat on the return line near the boiler wired in parallel with the circulator switching relay contacts. After a call for heat this would keep the circulator running until the return temp dropped below 135. The house temp would typically overshoot about 1-2 degrees barely noticeable. Reduced stand by loss as well as a longer burner run time due to a cooler boiler on start up by setting the stat a degree or two lower to control the overshoot. Only downside was a wider temp swing

hot_rod

EricPeterson said:

What about simply lowering the boiler setpoint so that the run cycle is longer?
Wait a minute - that's outdoor reset - maybe it's time for me to install that option on my ES2.
But it's $430.32 from SupplyHouse, I would like to first know the payback period be for this.
Based on my fuel cost of $1,484.36 for last year, and an estimated savings of 15% to 20% from US Boiler, the payback period would be a couple years.
So it's probably worth it?

Eric Peterson

Get that 15- 20% in writing🤭
With a cast boiler you will be limited on how low you can allow the boiler to go. Obviously not below where the boiler can get 130 return. If the system was designed around a 20 delta, the boiler needs to be above 150.
There is a Viessmann training about the effectiveness of ODR on different types of boilers and low or high mass distribution. Maybe it is online somewhere.

Another benefit of a buffer is that the tank runs at one temperature and the loads pull off via ODR. With low temperature radiant you could run possibly an 80 delta off the tank. If you have high temperature emitters, you may not leverage the tank that way

The lower, lowest, you can run your emitters, regardless of the type, the better you can leverage all this and keep efficiencies up.

fentonc

@EBEBRATT-Ed and @Steamhead - I've got a WM CGa-5-PIDN boiler that comes with its own controller that seems to have a built-in 20F 'swing' (is that the right term?). I can set the high limit and it will burn until it reaches that, then just circulates until it reaches ('high limit' - 20F), burn until the high-limit, etc. Would something like a "Hydrolevel Hydrostat" just replace the existing controller entirely, or would it be wired in parallel/in addition to it? The logic isn't immediately obvious to me - it would somehow need to replace the existing call for heat to the boiler, which monitors the water temperature. My typical burn time (after the initial burn) is less than 90 seconds, so anything that could increase the swing seems like it might help a lot.

hot_rod

MikeAmann said:

RayWohlfarth said:

I guess the key to better efficiency is to increase run time. @DanHolohan idea of installing a time delay relay on the burner to delay ignition while the circulator is pulling heat from the boiler will do that.

I still like my Intellidyne HW+ Economizer. It holds off the burner from firing allowing the circulator to continue running to use the heat already generated. This automatically means longer run times when the burner does fire. SAVINGS currently says 31.8% </p>

I see the value on an older cast boiler that has a lot of iron weight and water content

I see new cast boilers at the shows that only hold a few gallons and weigh not much more than a mod con. So the thermal flywheel has shrunk considerably, less residual heat to capture and distribute.

If you knew the boiler weight and volume you could get an idea of that heat scavenging.

I’d be curious to see how that 30% savings is calculated. Is it a measured value or an algorithm?

Maybe it’s when the burner is off 😂

DJD775

EBEBRATT-Ed said:

before I sold my house I had an oversized gas fired atmospheric boiler. 100,000 input with a 50,000 load.

I put a strap on reverse acting aquastat on the return line near the boiler wired in parallel with the circulator switching relay contacts. After a call for heat this would keep the circulator running until the return temp dropped below 135. The house temp would typically overshoot about 1-2 degrees barely noticeable. Reduced stand by loss as well as a longer burner run time due to a cooler boiler on start up by setting the stat a degree or two lower to control the overshoot. Only downside was a wider temp swing

I've been contemplating this strategy for circulator post purge but in my case I have a single circulator and zone valves. One way I've thought about overcoming this is by adding a differential bypass valve that would bypass one of the closed zone valves. The boiler is also connected to an indirect so in the off season I would either have to disable the post purge function or divert the bypass to the indirect zone.

hot_rod

MikeAmann said:

hot_rod said:

I’d be curious to see how that 30% savings is calculated. Is it a measured value or an algorithm?

Maybe it’s when the burner is off 😂

@hot_rod
You're close hot_rod, in actuality it's when the burner is HELD off.

There is a little more to it than this, but the simplest explanation is:
The HW+ gets wired to your aquastat. A temp sensor is strapped to the boiler's output pipe. A CFH still fires the burner up to the HI limit. The circulator is now running. Normally, that would continue until the AQ temp dropped 10 degrees below the HI limit (built-in fixed DIFF) - then the burner would fire again. But the HW+ looks at the output pipe temp and decides that there is plenty of heat left to hold off firing the burner and let the circulator continue to run until there really is a need to heat the water back up again. If I understand the unit correctly, the time that the burner is held off from firing is your calculated savings. My current settings are 170 for the AQ HI limit and 130 for the HW+ LO limit. Basically this gives me a 40 degree differential.

Basically forcing it to run at a 40∆? If it is holding the burner off for that period and a there is an active heat call, does it allow the boiler to fire regardless? Or does it need to drop to 130 before it fires?
If not is seems like a limiting device. Similar to using a delta T circ to constrain the output in an attempt to lengthen cycle. It "pulses" heat into the distribution at that decided operating parameter.

As long as it doesn't hold off or drop to low to maintain the heat load and comfort level, I suppose. If the load needs X amount of BTU/hr, it gets it a full boiler output, or a slowed down version of it.

STEVEusaPA

I wonder how it looks with an EK vs. the formulae?

DJD775

MikeAmann said:

DJD775 said:

EBEBRATT-Ed said:

before I sold my house I had an oversized gas fired atmospheric boiler. 100,000 input with a 50,000 load.

I put a strap on reverse acting aquastat on the return line near the boiler wired in parallel with the circulator switching relay contacts. After a call for heat this would keep the circulator running until the return temp dropped below 135. The house temp would typically overshoot about 1-2 degrees barely noticeable. Reduced stand by loss as well as a longer burner run time due to a cooler boiler on start up by setting the stat a degree or two lower to control the overshoot. Only downside was a wider temp swing

I've been contemplating this strategy for circulator post purge but in my case I have a single circulator and zone valves. One way I've thought about overcoming this is by adding a differential bypass valve that would bypass one of the closed zone valves. The boiler is also connected to an indirect so in the off season I would either have to disable the post purge function or divert the bypass to the indirect zone.

The new digital boiler controls have this function already built in. Look at the Hydrolevel or Beckett AquaSmart.

I have the hydro level and it only has pre-purge and I rather purge the boiler of heat at the end of the heat call. The Beckett has a timed post purge but I would still need something to keep the zone valve open or to bypass it. I like the idea of the strap on aquastat as you can select the desired temperature and not just a post purge time.

RayWohlfarth

Here is an example of an excel sheet I did comparing operating costs at different outdoor air temperatures. I used the entire hydronic system as a heat sink sort of by estimated the btus in the loop and converting that to temperature. I do this for my big commercial customers when selling boilers.

Ceacel

So, pretty much what Energy Kinetics has been saying for decades ?

Don’t trust the afue for boilers, they’re not as efficient as they’re rated.  

leonz

My coal stoker boilers 120,000 BTU efficiency equals the number of bags of coal I use per day
which is usually two 40 pound bags per day for the entire heating season.

80 pounds per day
2,400 pounds per month
My heating season October 1st to May 15th weather dependent with electric heaters early in the season as needed.

7 1/2 months+-

9 tons+- of Anthracite Rice coal to heat my home and domestic hot water.

archibald tuttle

EricPeterson said:

What about simply lowering the boiler setpoint so that the run cycle is longer?
Wait a minute - that's outdoor reset - maybe it's time for me to install that option on my ES2.
But it's $430.32 from SupplyHouse, I would like to first know the payback period be for this.
Based on my fuel cost of $1,484.36 for last year, and an estimated savings of 15% to 20% from US Boiler, the payback period would be a couple years.
So it's probably worth it?

Eric Peterson

in the day (actually not that many ago) TACO had a clunky version of ODR that included your circulator relay with a C terminal for 3 wire thermostats and NC/NO contacts in the SR501-OD which i used to buy not long ago for like a C-note. Now I'm hoarding the 4 I still got on the shelf. The industry could do this affordably although setback and postpurge has to me carefully implemented with legacy boilers that need non-condensing return temps and potentially higher stack temps to limit condensing in masonry chimneys.

JakeCK

hot_rod said:

What about simply lowering the boiler setpoint so that the run cycle is longer? Wait a minute - that's outdoor reset - maybe it's time for me to install that option on my ES2. But it's $430.32 from SupplyHouse, I would like to first know the payback period be for this. Based on my fuel cost of $1,484.36 for last year, and an estimated savings of 15% to 20% from US Boiler, the payback period would be a couple years. So it's probably worth it? Eric Peterson

Get that 15- 20% in writing🤭 With a cast boiler you will be limited on how low you can allow the boiler to go. Obviously not below where the boiler can get 130 return. If the system was designed around a 20 delta, the boiler needs to be above 150. There is a Viessmann training about the effectiveness of ODR on different types of boilers and low or high mass distribution. Maybe it is online somewhere. Another benefit of a buffer is that the tank runs at one temperature and the loads pull off via ODR. With low temperature radiant you could run possibly an 80 delta off the tank. If you have high temperature emitters, you may not leverage the tank that way The lower, lowest, you can run your emitters, regardless of the type, the better you can leverage all this and keep efficiencies up.

Is there a penalty in efficiency when you run a buffer tank with a large delta say it cuts out at 180 and allows it drop to 130 before it kicks the boiler back on? As the delta between the flue temperatures and hx and water temp shrinks the rate of heat transfer slows does it not? Does the longer cycle times more than make up for this?

hot_rod

JakeCK said:

hot_rod said:

EricPeterson said:

What about simply lowering the boiler setpoint so that the run cycle is longer?
Wait a minute - that's outdoor reset - maybe it's time for me to install that option on my ES2.
But it's $430.32 from SupplyHouse, I would like to first know the payback period be for this.
Based on my fuel cost of $1,484.36 for last year, and an estimated savings of 15% to 20% from US Boiler, the payback period would be a couple years.
So it's probably worth it?

Eric Peterson

Get that 15- 20% in writing🤭
With a cast boiler you will be limited on how low you can allow the boiler to go. Obviously not below where the boiler can get 130 return. If the system was designed around a 20 delta, the boiler needs to be above 150.
There is a Viessmann training about the effectiveness of ODR on different types of boilers and low or high mass distribution. Maybe it is online somewhere.

Another benefit of a buffer is that the tank runs at one temperature and the loads pull off via ODR. With low temperature radiant you could run possibly an 80 delta off the tank. If you have high temperature emitters, you may not leverage the tank that way

The lower, lowest, you can run your emitters, regardless of the type, the better you can leverage all this and keep efficiencies up.

Is there a penalty in efficiency when you run a buffer tank with a large delta say it cuts out at 180 and allows it drop to 130 before it kicks the boiler back on? As the delta between the flue temperatures and hx and water temp shrinks the rate of heat transfer slows does it not? Does the longer cycle times more than make up for this?

The wider the delta the more heat you. Transfer 500Xflow(delta t). The low return to the boiler raises efficiency a bit.

Every time you move or transfer energy a bit slips away.
Tank standby loss would be inside the heated envelope?

So you want to look at how bad the efficiency is at low loads, short cycles. How often at those low $$ efficiencies. The cost to implement a buffer based against the possible savings.

For me, just to not hear those short cycles.
, all the time is worth the entry fee.

The control @MikeAmann mentioned probably has the most benefit on oversized, grossly oversized boilers to get the run cycle more realistic. I don’t see as much value on a properly sized, new lightweight cast boiler on a low mass system like fin tube. As @EBEBRATT-Ed mentioned I’d depends on how much overshoot it caused, the heat needs to purge somewhere. The EK system puts it into the DHW which makes sense.

JakeCK

Allow me to clarify. In my case my boiler is always running borderline on condensing. I've only ever seen it bounce off the aquastat, which is set at 170 I believe, maybe three times in the 13 years I have lived here now during normal operation. If I installed a buffer tank the swt would most definitely be higher than it is right now. With a 50 degree swing between 130 to 180F. My concern would be that since a good part of its cycle would be closer to 180 than it's current operating temperature it would not be as efficient as one would expect.

This is why I would like to install an a2w hp because if I kept the radiators at a steady temperature based on ODR they would probably never go much above 130 at design or higher. And I have yet to insulate the walls.