When is a high efficiency condensing boiler not a high efficiency condensing boiler?

 
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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

Post by lsayre » Sat. Feb. 20, 2021 9:44 am

Bosler Brothers applies a rather painful up-charge to me due to having to travel about 82 miles by road each way (164 mile round trip) to deliver 5 tons max (usually in actuality this wound up to be only ~4.8 delivered tons, but their flat rate up-charge is made worse for that case). And Coalway is under new ownership and (surprise, surprise) their coal (and compressed sawdust wood bricks) prices went up noticeably, plus at ~26 miles one way to me by road they also apply an up charge. I'm basing my pricing for anthracite on ~$250 per delivered ton, plus tax. And for those who are wondering, yes, Ohio taxes coal at the full going retail sales tax rate, which for me is 6.75%. My tax paid on NG is only 4.25% for comparison.

 
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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

Post by lsayre » Wed. Mar. 03, 2021 10:03 am

It turns out that until today my $ tracking spreadsheet lines had errors in them which I've just fixed. Some months had sums which were pointing to a few incorrect cells. Here is how the fuels stack up for me as of the spreadsheet fix:

Relative fuel cost comparison for combined home heating and DHW from April 1, 2020 through March 2, 2021:

NG = $1,217
Coal ~= $1,281
Electricity ~= $2,742

5,220 HDD's here from April 1, 2020 through March 2, 2021.

The coal $$ deficit to NG accumulates within the period of roughly mid May through early/mid Oct. when most of the usage is for DHW only here in these parts of the USA, whereby coal is terribly inefficient for covering that task exclusively. During the really cold months from Dec. through Feb. coal heating is actually cheaper than NG. During months not listed they are about equal in cost.

 
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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

Post by lsayre » Mon. Mar. 22, 2021 10:46 am

Based upon HDD's to date this year, plus past historical HDD's, and past electrical consumption data for when we heated with resistance electric, and all of my coal burning data, the current relative "overall" home heating efficiencies (as best as I can estimate them) between the three units I've used to heat our home are:

Natural Gas Boiler ~= 77% efficient (vs. rating of 86%-95% for non-condensing to fully condensing conditions)
S-130 Coal Gun Boiler ~=68% efficient (and is supposed to be ~80.5% efficient)
Resistance Boiler = 100% efficient (presumed simply by definition for resistance heating)

Either I'm computing this quite wrongly, or heating appliances rated efficiencies are not to be trusted, or it was (on average) warmer during the winters for which we heated with electricity, whereby my baseline estimate of required BTU's per HDD may be way off. ???? My baseline estimate is 12,480 BTU's per HDD. Trying to back out DHW heat demand is also definitely interfering and messing with the home heating data....
Last edited by lsayre on Mon. Mar. 22, 2021 10:58 am, edited 1 time in total.


 
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Rob R.
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Post by Rob R. » Mon. Mar. 22, 2021 10:56 am

lsayre wrote:
Mon. Mar. 22, 2021 10:46 am

Either I'm computing this quite wrongly, or heating appliances rated efficiencies are not to be trusted, or it was (on average) warmer during the winters for which we heated with electricity. ????
You are calculating something different - which is the overall efficiency of an appliance over a heating season. Steady-state efficiency will naturally be higher, b/c it doesn't allow for any energy required to keep the boiler at operating temperature when there is no demand.

Your NG and electric boiler can go to room temperature when there is no heat demand, that is not the case with a coal boiler.

 
Holdencoal
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Post by Holdencoal » Mon. Mar. 22, 2021 10:57 am

Have you looked at the French made FCX oil boiler? 93% efficient....🤔

 
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lsayre
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Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Lehigh Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW), ComfortMax 75

Post by lsayre » Mon. Mar. 22, 2021 11:04 am

Holdencoal wrote:
Mon. Mar. 22, 2021 10:57 am
Have you looked at the French made FCX oil boiler? 93% efficient....🤔
I'd have to hook it up to my house in order to see what its measured "overall real world efficiency" in my home winds up being. My initial guess is about 75% overall (real world) efficiency though.

PS: It is only 'potentially' 93% efficient when it is seeing 100% condensing weather type conditions. In the dead of winter it will be de-facto about 10% less efficient, as it will not be seeing condensing conditions then.


 
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lsayre
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Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Lehigh Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW), ComfortMax 75

Post by lsayre » Mon. Mar. 22, 2021 11:11 am

As I understand it, my natural gas boiler is likely just beginning to condense a wee bit when returning water is at about 130 degrees F., and it is likely 100% condensing for return water at somewhere around 110 degrees F and below.

Call it 87% efficient with ~130 degree return water and 95% efficient with ~110 degree (or colder) return water.

Condensing and boilers are not a very good fit for each other. And my current (ancient) hot water baseboards are not a good fit for a condensing boiler either. They can't emit sufficient heat for a return at or below 130 degrees. I could improve things somewhat by going with "high output" hot water baseboards, which deliver as much heat as my current baseboards when the water passing through them is 20 degrees colder. The most "priced through the roof" baseboard, which has twin heating elements stacked one atop the other, might deliver as much heat as my current baseboards with 25-30 degree colder water.
Last edited by lsayre on Mon. Mar. 22, 2021 11:54 am, edited 1 time in total.

 
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lsayre
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Posts: 21784
Joined: Wed. Nov. 23, 2005 9:17 pm
Location: Ohio
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Lehigh Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW), ComfortMax 75

Post by lsayre » Mon. Mar. 22, 2021 11:27 am

For things "as they are", I'm saving an estimated $1,625 vs. heating my home and DHW with resistance electricity over the past year. About the same for NG as for coal in this regard.

 
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lsayre
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Posts: 21784
Joined: Wed. Nov. 23, 2005 9:17 pm
Location: Ohio
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Lehigh Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW), ComfortMax 75

Post by lsayre » Sun. Mar. 28, 2021 6:18 am

If I do my best to factor out DHW, and I exclude all of the non-heating months, and measure the efficiency of my Coal Gun only upon the basis of home heating during the heating season, its overall annualized efficiency for exclusively home heating becomes 73.4%.

I'm basing this upon my current best guess that each HDD requires 12,480 BTUH whereby to maintain 70 degrees for my house. And my need (long term average) for ~1.385 Lbs. of anthracite burned per HDD experienced. And upon an assumed 12,275 BTU's per pound of average anthracite on an "as received, or A.R." basis.

12,480/(1.385 x 12,275) = 0.73408 = 73.41% efficiency

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