Wood Cords Equivalent Energy Usage

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jebatty

Minister of Fire
Jan 1, 2008
5,796
Northern MN
What's your total wood equivalent energy usage in 2011? Ours was 4.3 cords red oak equivalent (3757 lbs/cord).

We just got from Mrs. Electric a report of our total electrical usage in 2011: 11,959 kwh. Our DHW heating is on a separate meter, and that is a little less than 1/2 of the total. We also burned about 4 cords of aspen/pine for space heating (about 2.5 cords red oak equivalent). 1500 sq ft house with full basement, 3000 sq ft total. 10,350 heating degree days in 2011 at base 70F.

Both electric and wood use is energy, so the electric use equals another 6750 pounds of wood, or another 1.8 cords red oak equivalent (6050 btu/lb x 6750 / 3412 btu/kwh = 11,969 kwh). Therefore, total energy used for our house in 2011 was 4.3 cords red oak equivalent for a year. We don't use any coal, oil, LP or natural gas for the house; just wood and electric.
 
Another interesting number: 3.72 btu/hr/sq ft total annual energy usage.

4.3 cords red oak equivalent (3757 lbs/cord) total energy use = 4.3 x 3757 x 6050 btu/lb = 97,738,355 btu/yr / 365 = 267,776 btu/day / 24 = 11,157 btuh / 3000 sq ft = 3.72 btu/hr/sq ft total annual energy usage.
 
Jim,

6050 btu/lb is assuming what efficiency? Something over 90% based on 20% mc?
 
Wood at 20% MC and 400F flue temp has available energy of 6050 btu/lb. Energy I'm assuming both in my calculations. My wood is dried 2-3 years under cover from rain/snow. The 400F flue temp is somewhat idealistic for the wood stove that heats the house. In all events this does give an interesting perspective on energy usage.
 
Very interesting, Jimyou know they make woodgas generators, as long as you are feeding one fire already, with all that ready wood and shop space!
 
I've got the plans for a wood gas generator, now I just need the time. My thought was to make one to produce wood gas for the electric generator, thus being free of a need for gasoline in a major emergency.
 
As efficient as these boilers are at making hot water ,one of us should figure out how to make electricity with them. That would be ideal.
Running an internal combustion engine on woodgas has been around for a long time and it works,but I don't know if its as easy as it looks on utube.
 
Jim,
I installed a Love digital controller(TCS 4010) with J-thermocouple in my boiler's exhaust(where it funnels down into 6") to monitor exhaust stack temperatures. I've also installed a solenoid with an adjustable air flow "flap" to restrict air flow when when stack temperatures reach 290*. I've programmed a 10* differential in, so when stack temps drop back down to 280*, more air is fed in. I've logged more than 40 hours monitoring exhaust temps, and the average temperature is 286* while under gasification.
How many BTU's/lb would you suspect I'm getting with 20% mc White Ash?
I am not getting any condensation in my exchange tubes or triple wall stack. My wood usage during my not-so-scientific testing appears to have gone down between 10 and 20%. I installed another pump to prevent stratification during testing, as well as unplugging the pump that feeds the house.
Do you think my new stack temps are too low? I'm getting a bit more fly ash in my exchange tubes, but I believe that is a direct result of decreased air movement. I would think fine particulate emissions overall should be reduced.
Your opinions would be greatly appreciated.
Do me a favor and don't tell P&M I'm voiding my warranty by drilling holes for thermocouples and combustion analyzer probes ;-)

Thanks Jim,

Marty
 
... to restrict air flow when when stack temperatures reach 290*. I’ve programmed a 10* differential in, so when stack temps drop back down to 280*, more air is fed in. I’ve logged more than 40 hours monitoring exhaust temps, and the average temperature is 286* while under gasification.

I do not experience temps that low, possibly because my wood is very dry pine and aspen. Based on what I've read, I think you're as low as you want to go. Pay close attention to make sure you are not getting any condensation in your stack or hx tubes, to make sure you have no creosote in the stack or other buildup, especially near the top where the exhaust gases would be the coolest. If it works and no problems, I likely would accept what you are experiencing. Maybe others have more experience or better advice.

If you need more output from your boiler, you can allow higher stack temperatures.

[/quote]How many BTU’s/lb would you suspect I’m getting with 20% mc White ash?[/quote]

I don't think the species of wood will make much difference. Assuming a 300F stack, I would estimate 6050 x 1.03 = 6230 btu/lb in round numbers.
 
... to restrict air flow when when stack temperatures reach 290*. I’ve programmed a 10* differential in, so when stack temps drop back down to 280*, more air is fed in. I’ve logged more than 40 hours monitoring exhaust temps, and the average temperature is 286* while under gasification.

I do not experience temps that low, possibly because my wood is very dry pine and aspen. Based on what I've read, I think you're as low as you want to go. Pay close attention to make sure you are not getting any condensation in your stack or hx tubes, to make sure you have no creosote in the stack or other buildup, especially near the top where the exhaust gases would be the coolest. If it works and no problems, I likely would accept what you are experiencing. Maybe others have more experience or better advice.

If you need more output from your boiler, you can allow higher stack temperatures.

How many BTU’s/lb would you suspect I’m getting with 20% mc White ash?

I don't think the species of wood will make much difference. Assuming a 300F stack, I would estimate 6050 x 1.03 = 6230 btu/lb in round numbers.
 
martyinmi said:
I've also installed a solenoid with an adjustable air flow "flap" to restrict air flow when when stack temperatures reach 290*. I've programmed a 10* differential in, so when stack temps drop back down to 280*, more air is fed in. I've logged more than 40 hours monitoring exhaust temps, and the average temperature is 286* while under gasification.
Super. Need photos! I want to set something like this up for my barbeque early this spring.
Do you think my new stack temps are too low?
Might be pushing it a little, you only give up about 1% per 30 degF if you go a little higher, so I've been aiming to err on the high side just to play it safe. Plus my particular boiler seems to need to run a little harder to stay clean and steady.

--ewd
 
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