Something to Ponder for the 'Whole House' Stoker Gang

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lsayre
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Stoker Coal Boiler: AHS S130 Coal Gun
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Location: N/E Ohio, between Medina and Wadsworth

Post Wed. Jul. 09, 2014 7:54 pm

I've been toying with my coal consumption numbers again, and I've noticed that my single highest days coal consumption for a heating season is roughly in the ballpark of my entire heating seasons average daily coal consumption times 2.4. I was just wondering if this incredibly loose 2.4x "rule of thumb" (no science need apply here) holds true for others who heat their home exclusively with a stoker (or with multiple stokers)?

OK, the hand fired guys and gals can tell us their experience also.


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Rob R.
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Post Wed. Jul. 09, 2014 8:30 pm

Pretty close. I average 60 lbs per day for the season, and the most I burn in 24 hrs is 150-160 lbs.

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lsayre
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Location: N/E Ohio, between Medina and Wadsworth

Post Wed. Jul. 09, 2014 8:46 pm

To simplify things, let's call it the "rule of 2.5X".

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Sting
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Post Wed. Jul. 09, 2014 9:14 pm

Take a look at the heating degree days charts and how the curve gets steeper as the temp goes down

then compare your heating degree day to the coal consumption of the day :shock:

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lsayre
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Stoker Coal Boiler: AHS S130 Coal Gun
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Location: N/E Ohio, between Medina and Wadsworth

Post Wed. Jul. 09, 2014 10:21 pm

This certainly needs a lot more contributors in order to settle on a more solid factor that for now tentatively stands at 2.5X for this rule of thumb, but one practical thing I can see using it for is as follows:

If you generally know how much coal you have burned for a season, but you did not at all pay attention to your coal usage on a daily basis, you can simply apply this "rule of 2.5X" to get at least a ballpark understanding of the actual heat loss requirement of your home.

For example, if you burn roughly 6 tons of coal over a roughly 7 month heating season that is roughly 12,000 lbs. burned over about 210 days, or an average of about 57 lbs. burned per day.

Take this 57 lbs per average per day and multiply it by the 2.5X rule of thumb to get 143 lbs.

143 lbs. / 24 hours = 6 lbs. of coal per hour.

On an "as delivered" basis each lb. of coal can be assumed to have about 12,150 BTU's. And at an 80% efficiency of burn you can capture about 9,720 of those BTU's for practical home heating.

6 lbs. per hour x 9,720 BTU's/lb. = 58,320 BTUH

Thus (after allowing for a slight bit of upward rounding) your heat loss ballpark for your home for this particular example is roughly 60,000 BTUH.

Any heating appliance which can reliably deliver an output of 60,000 BTUH should nominally suffice to keep you warm all year round (provided that the year you used initially to get to you this point in my rambling is highly representative of a normal year).

Divide this by the efficiency rating of the appliance and you then have calculated the required input BTUH's to heat your home. If your furnace, boiler or stove (or one you are looking at for the future) is 80% efficient, then 60,000 / 0.80 ~= 75,000 BTUH.

Since nearly all heating appliances are rated by their input BTUH's, you now know that if your appliance of choice (or of your dreams) for this example case has a rated input of at least 75,000 BTUH you should be good to go.

The same general 2.5X rule of thumb should apply for any fuel of your choice.

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michaelanthony
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Post Thu. Jul. 10, 2014 10:02 am

...Ok my 2 cents, last winter was the exception but it was also enlightening for us rebels with a cause. When the temps plummet and hold for period of time I see my shake and load times change. They go from 12 -14 hrs. to 10 -12 hrs. I also noticed that my Vigilant responds better and seems to burn coal more efficiently ( fine, fine powder ) when the temp is around zero degrees. I will add the default response that my set up and chimney and home like everyone else's is different and this may play a part...but I was invited to this dance :D ...so I would guess a 15% increase in consumption should cover it.

Maybe having a hand fed in my living room and not a boiler in the basement saves me heat loss one would experience with pipes and various line loss in a non-living space :?

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lsayre
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Location: N/E Ohio, between Medina and Wadsworth

Post Thu. Jul. 10, 2014 10:53 am

michaelanthony wrote:... Maybe having a hand fed in my living room and not a boiler in the basement saves me heat loss one would experience with pipes and various line loss in a non-living space :?
I pretty much surmised that this 2.5X rule of thumb would be a stoker regulated by T-Stat(s) thing that would not correlate well to hand fed consumption patterns.

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michaelanthony
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Post Thu. Jul. 10, 2014 11:26 am

[quote="lsayre"][quote="michaelanthony"]... Maybe having a hand fed in my living room and not a boiler in the basement saves me heat loss one would experience with pipes and various line loss in a non-living space :?[/quote]

I pretty much surmised that this 2.5X rule of thumb would be a stoker regulated by T-Stat(s) thing that would not correlate well to hand fed consumption patterns.[/quote]

I realize that but you said the hand fed guys and gals can tell you their experience. I digress surely you didn't mean a hand fed stoker...hey I called you sur........oh never mind one of the funniest movies evah! Good luck with your survey.


Pacowy
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Post Thu. Jul. 10, 2014 11:39 am

lsayre wrote:Any heating appliance which can reliably deliver an output of 60,000 BTUH should nominally suffice to keep you warm all year round (provided that the year you used initially to get to you this point in my rambling is highly representative of a normal year).
The 2.5X figure reflects approximately the coldest day/average day coal consumption we've experienced (with a thermostat-controlled stoker boiler). However, in converting daily coal consumption to a required output capability, it seems like you are implicitly assuming that the unit will run 24 hours on the coldest day, and that the user is willing to endure cold house temps during the colder part of the day. In our case, the system actually ran for about 14 hours on the coldest day. If we had to run it for 24 hours to get out the BTU's we needed we would have been cold for a while. "To keep you warm all year" I believe you need an hourly output capability higher than shown by the formula.

Mike

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Rob R.
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Post Thu. Jul. 10, 2014 1:19 pm

average load over 24 hrs and peak load are two different things.

14 hrs is also my maximum stoker run time in 24 hours...but with the same settings I have also seen the boiler run for 3-4 hours nonstop during extreme weather conditions.
Sting wrote:
then compare your heating degree day to the coal consumption of the day :shock:
My days with highest consumption were not on the day with the most degree days. For my home, -20F with no wind is "a breeze" compared to 0F with a 15 mph (or 25 mph :shock: ) sustained wind. I am probably an unusual case because I live in an old home out in the middle of a large open area, but it is a good example of worst case conditions for a given year vs. design conditions. I can choose to design for the OF and 25 mph days, or not.

Pacowy
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Post Thu. Jul. 10, 2014 1:52 pm

Rob R. wrote:14 hrs is also my maximum stoker run time in 24 hours
Based on this sample of 2, I would suggest amending the formula for sizing the appliance to account for the heat load variations within a day as follows:

2.5 x (24/14) x average consumption, or 4.3 x average consumption

Miraculously, this formula replicates the stoker feed rate we use, which has maintained set temps for the 4 winters we have been in this house.

Mike

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Sting
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Post Thu. Jul. 10, 2014 3:13 pm

Rob R. wrote: My days with highest consumption were not on the day with the most degree days. For my home, -20F with no wind is "a breeze" compared to 0F with a 15 mph (or 25 mph :shock: ) sustained wind. I am probably an unusual case because I live in an old home out in the middle of a large open area,
you not unusual - your UNIQUE :P

I am sure the mayor can affirm that coal and oil deliveries were delivered on time by heating degree day use. Each customer had a factor to apply = yours might have been a little more than others.

With out some bench mark [ such as HDD ] your just throwing darts -- and you may still be

It Depends.

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lsayre
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Post Thu. Jul. 10, 2014 5:18 pm

Pacowy wrote:The 2.5X figure reflects approximately the coldest day/average day coal consumption we've experienced (with a thermostat-controlled stoker boiler). However, in converting daily coal consumption to a required output capability, it seems like you are implicitly assuming that the unit will run 24 hours on the coldest day, and that the user is willing to endure cold house temps during the colder part of the day. In our case, the system actually ran for about 14 hours on the coldest day. If we had to run it for 24 hours to get out the BTU's we needed we would have been cold for a while. "To keep you warm all year" I believe you need an hourly output capability higher than shown by the formula.

Mike
Well noted! Some percentage of safety margin above my methods bare minimum results should perhaps be assumed, as my method is pretty much cutting things to the quick. After the HVAC guys calculate a homes heat loss, how much padding factor do they (or better, should they) apply above that level in order to size a furnace or boiler?

We are now up to 3 stoker with T-Stat(s) users who agree with the 2.5X factor and zero who disagree.

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lsayre
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Stoker Coal Boiler: AHS S130 Coal Gun
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Other Heating: Resistance Boiler (13.5 KW), ComfortMax 75
Location: N/E Ohio, between Medina and Wadsworth

Post Thu. Jul. 10, 2014 6:32 pm

For my case, wherein on the coldest day of the coldest year in a decade I burned 110 lb's of coal, then for coal my homes heat loss is about 44,550 BTUH.

110/24 x 12,150 x 0.80 = 44,550 BTUH

Back when we were all electric for a full decade the most electricity we used in one year was 30,000 KWH. And now that we have the coal boiler our electricity demand is only 6,500 KWH per year. 30,000 - 6,500 = 23,500 KWH for heat. But for electricity we only heated the home to 62 degrees when we were asleep or not home, and to 68 degrees when we were awake and at home. Call it 65 degrees on average. We now keep the house at 69 degrees. So using my 2.5% more energy demand per degree of rise rule, the 23,500 KWH must be multiplied by 4 x 2.5% or 10%.

23,500 KWH for 65 degrees x 1.1 = 25,820 KWH for 69 degrees

25,820 KWH / 210 days of heating season = 123 KWH per day on average

Multiply by the "rule of 2.5X" and the estimated heat demand for the coldest single day in our decade of heating via electricity becomes 307.5 KWH

Multiply this by 3,412 BTU's per KWH, and the result is 1,049,190 BTU's for this entire 24 hour coldest day.

Then divide by 24 to get our homes heat loss estimate via electricity at 43,700 BTUH.

By comparison, 44,550 BTUH of heat loss calculated for coal and 43,700 BTUH of heat loss calculated for electricity are within ~2%.
Last edited by lsayre on Thu. Jul. 10, 2014 6:54 pm, edited 2 times in total.

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Sting
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Post Thu. Jul. 10, 2014 6:40 pm

lsayre wrote: We are now up to 3 stoker with T-Stat(s) users who agree with the 2.5X factor and zero who disagree.
STING = chopped liver :oops: :mad:


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