Wood Stove vs. Coal Boiler efficiency

 
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McGiever
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Post by McGiever » Fri. Dec. 29, 2017 11:16 am

franco b wrote:
Fri. Dec. 29, 2017 10:15 am
Half the heat in wood is in the gas. Not burning it means smoke, but burning it overwhelms the heat exchange.

The problem was solved hundreds of years ago with massive masonry heat exchange, or in modern stoves with pellet feed a little at a time steadily.
Well said! :yes:

Hate to say it but Larry would be well served aside from burnig coal in this stove to use a wood pellet stove to gain the burn control results he desires. :)


 
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Post by lsayre » Fri. Dec. 29, 2017 12:12 pm

McGiever wrote:
Fri. Dec. 29, 2017 11:16 am
Well said! :yes:

Hate to say it but Larry would be well served aside from burnig coal in this stove to use a wood pellet stove to gain the burn control results he desires. :)
But then I would need to have electricity. One reason for this stove was to heat the house during power outages. I did see a non-electric gravity stoking pellet stove somewhere though. No idea if it would be reliable, or what output it is rated for.

 
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Post by lsayre » Mon. Jan. 01, 2018 9:51 am

Nearing 7 full days of burning wood and coal together, and it appears now that the wood burned in the wood stove is only displacing about 56% of the coal consumption that it should theoretically be displacing in the coal boiler. A deficit of 44%.

 
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Post by Rob R. » Mon. Jan. 01, 2018 10:01 am

Imagine how you would feel if you spent 10k on a wood boiler and had the same results.

 
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Post by lsayre » Tue. Jan. 02, 2018 7:31 am

I've switched from feeding the stove 4 x 3.5 lb. blocks of compressed sawdust every 5.5 hours (~20,000 input BTUH) to 3 blocks every 5 hours (~16,500 input BTUH). That should tone down the overheating, and also narrow the wood deficit to coal a bit.

 
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Post by lsayre » Wed. Jan. 03, 2018 5:02 am

So how much coal am I still burning when I have the ComfortMax burning on wood in my living-room? Overall, the ComfortMax is only reducing my boilers coal consumption by 31.5% to date. Effectively it has stopped coal consumption only in the living-room zone of my home. The Bedroom, Basement, and Garage zones are still firing the boiler. It is doubtful that the ComfortMax operating alone could even come close to keeping my entire house warm if called upon to do so. I would need two additional ComfortMax stoves in order to properly heat it without the boiler running.

If I abandon the garage to the cold, and allow the bedroom zone to get into the very low 60's at night, and I heat my basement with a stove, we could probably eek by on one additional stove instead of two. But then the hot water baseboard loop in the garage would likely freeze and bust, unless I add propylene glycol to my boiler.

 
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Post by Rob R. » Wed. Jan. 03, 2018 5:30 am

Larry, can you open your zone valves to allow gravity circulation in the event of a power outage? If so, and you lean an pipe against the flap over the fire door, the S130 will continue to put some heat into the house.


 
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Post by lsayre » Wed. Jan. 03, 2018 6:22 am

Rob R. wrote:
Wed. Jan. 03, 2018 5:30 am
Larry, can you open your zone valves to allow gravity circulation in the event of a power outage? If so, and you lean an pipe against the flap over the fire door, the S130 will continue to put some heat into the house.
I should be able to remove the motor from each zone valve and then manually open them. Thanks for this suggestion.

 
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Post by lsayre » Wed. Jan. 03, 2018 7:55 am

lsayre wrote:
Wed. Jan. 03, 2018 6:22 am
I should be able to remove the motor from each zone valve and then manually open them. Thanks for this suggestion.
I just thought this through, and since my circulator has a built in check valve, I will not be able to utilize thermosiphon.

 
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Post by hotblast1357 » Wed. Jan. 03, 2018 7:57 am

What would u be gaining anyways??

 
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Post by Rob R. » Wed. Jan. 03, 2018 8:09 am

Hot water heater without power. At the least it should keep pipes from freezing.

Larry, there should be no need for that check valve if you are running zone valves. It is easy enough to remove if you are motivated to do so.

 
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Post by CapeCoaler » Wed. Jan. 03, 2018 11:09 am

The only way to heat with chunk wood...
Is the 'masonry heater'....
Massively efficient...
No power needed...

 
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Post by lsayre » Sun. Jan. 07, 2018 9:34 am

With the promise of warmer weather beginning post noon today, my wood stove will be allowed to burn out by roughly 2:00 PM today. That will be 13 full days of burning wood (along with coal).

In the end it saved me only 283 lbs. of coal (or ~3,466,750 BTU's worth) at the expense of burning ~230 x 3.5 lb. sawdust blocks (or ~6,299,125 BTU's worth).

6.3 million BTU's of wood to displace 3.5 million BTU's of coal is not very efficient. Roughly 1.8 wood BTU's were expended to replace each coal BTU saved.

With respect to my coal boiler, the wood stove is in the end only ~56% as efficient, on the basis of BTU input for BTU input. Allowing for how much warmer the zone being heated by wood was during this entire period, I conclude that in actuality the wood stove is roughly 62% as efficient as the Coal Gun boiler. That puts the wood stove right at about 50% overall "real world" efficiency (vs. an advertised 92% efficiency).

Conclusion: If you plan to heat your home with wood, calculate how much you think you "should" need, then multiply that by 1.8 (to 2) to be on the safe side and have enough on hand to make it through the season.

 
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Post by Lightning » Sun. Jan. 07, 2018 12:06 pm

Wow, those are some startling numbers Larry and pretty solid conclusions too. I wonder if split wood would be any better or worse than the fuel blocks.

Nice work!

Edit - Is DHW factored into that, or doesn't it need to be?

 
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Post by lsayre » Sun. Jan. 07, 2018 12:42 pm

Lightning wrote:
Sun. Jan. 07, 2018 12:06 pm
Wow, those are some startling numbers Larry and pretty solid conclusions too. I wonder if split wood would be any better or worse than the fuel blocks.

Nice work!

Edit - Is DHW factored into that, or doesn't it need to be?
I used HDD's and my computer spreadsheet accounts for DHW demand, so it is factored in.

I assumed 7,825 BTU per pound for the compressed sawdust wood blocks based on only 6 to 8 percent moisture. Well seasoned hardwood delivers (for the absolutely best case scenario of only 20% moisture) 6,750 BTU's per pound (and real world it is highly likely to be less, call it 6,250 BTU/Lb.).

I heated my previous home exclusively on mixed split hardwoods for the first two years we lived in it. My experience with the typical loading frequency with the blocks (in order to regain a fire without taking extraneous measures) is nearly identical to my experience with split hardwoods.

For what it's worth, mixed, unseasoned, and highly green hardwoods have only about 2,600 BTU's per pound (based upon 60% moisture). Wood at a hypothetical zero percent moisture would have about ~8,400 BTU's per Lb. And also for what its worth, when metering wood by the pound instead of by volume, a pound of soft pine wood at 25% moisture (etc...) and a pound of hickory or oak (etc..., when also at 25 % moisture) both have ~6,400 BTU's.
Last edited by lsayre on Sun. Jan. 07, 2018 1:24 pm, edited 5 times in total.


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