Nice video on visually showing how much water is in wet wood

[precaud]

As far as the bomb calorimeter, what's the point? That's still theory unless we start to heat our homes that way. Hell, we're almost there with all the insulation they add to a stove these days. Instead, though, why not ask a real wood heating scientist to compared the overall heating efficiency of a couple real life stoves in a very tightly-controlled laboratory test, using both green wood and seasoned wood the way the average homeowner would burn them and compare the results?

The columns in tan are seasoned oak at 21% MC, the ones in green are green oak burned at 41% MC (both dry-basis). Not 45% less heat in the room... not remotely close to 45%. In fact, about a 5% heat loss from all the variables that should result in heat loss, including the heat of vaporization. Note that the green oak was even more efficient when burned in an open (AKA "Franklin") stove. On the right is a conventional air-tight stove and way over on the left? A Blaze King catalytic stove... which some folks here will tell you won't even burn green wood at all.

BK, here's something else to consider about the burn cycles in that test:

"For mains loads, the end of a phase was defined as the point when the fuel weights had decreased to the weight of the original charcoal bed, i.e., when a weight of fuel corresponding to that of the main load had been burned."

I don't think this reflects normal use - it doesn't reflect mine. Much of the heat output in the test is in the charcoal phase, where differences between stoves are minimal. I really wish he had published graphs of output level vs time over the 24-hour period so we could see each stove's cycle and see it repeat.

Also the bit on p. 18 about adding fuel in the interphases in order to maintain a 20% charcoal bed, and "sometimes wood was added to raise the temperature of the stove to the desired level." Some loads got juiced beforehand, some didn't.

 

[Renovation]

Hi Battenkiller,

Many thanks for your encouragement, kind words, and for taking my curiosity in the spirit in which I intend it. You brightened my day!

George, you do realize that I didn't do this study, don't you? I didn't decide anything, Dr. Jay Shelton of Shelton Research, Inc. did all the deciding back in 1986.

:red:
(Where's the "D-oh!/facepalm" icon when you need it?)

Very cool data, nonetheless.

The overall efficiency was determined by using information gathered from numerous sensors strategically placed in the flue (see diagram below). This is called the the "stack loss method", and is used throughout the industry, both in the design phase and during testing

Is this similar to the setup in the photo of Woodstock's prototyped stove? I noticed it was setting on a scale, and thought that was very cool.

It is the custom in North America to use the higher heating value (probably to make the stoves appear more energy efficient). This leads to a lot of confusion as well as yielding a figure that no one is interested in knowing. We want to know how much heat is coming into the room for every ounce of wood we burn. The industry is usually not giving us the correct answer, and we have no sure way of knowing when they are.

Very helpful, thanks. I've pondered over that in manufacturer's specs.

Shelton Research used a much more realistic method to determine overall heating efficiency by subtracting all energy loses (chemical energy, sensible heat lost up the flue, and latent heat losses through evaporation). This method correlates highly with heat output testing of wood stoves done in actual calorimeter rooms, so it is considered to be very accurate.

Understood. Excellent!

The formulas Shelton used were:


Overall efficiency = (wood energy input minus sensible heat loss minus chemical energy loss minus latent heat lost) divided by wood energy input

Combustion efficiency = (wood energy input minus chemical energy loss) divided by wood energy input

Heat transfer efficiency = (wood energy input minus sensible heat loss minus chemical energy loss minus latent heat lost) divided by (wood energy input minus chemical energy loss)

Makes sense to me. I haven't looked at the paper yet--offhand can you tell me the definition of "sensible heat loss"?

By using the lower heating value (values in the chart I posted above) instead of the higher heating value (usually used in North America) for expressing wood energy, he was able to compute the latent heat loss from unrecondensed water vapor leaving the flue based on the assumption of complete combustion without any effect on the accuracy of the data.

Okay, that answers my original question--the data corresponds to the energy a consumer would actually get from their stove, when burning dry wood, wet wood, etc.

So, back to your original post on this, the upshot is that in this study wet wood burned nearly as efficiently as dry, and that was your counter-intuitive point?

That is indeed shocking, given the reports here.

But, not having looked at the study, I'm guessing the stoves used were pre-EPA smoke dragons?

Does that explain a lot of the posts here? Namely:

1. Burners with smoke dragons (or with friends with same) reporting that seasoning is a crock, and they burn green wood all the time with no problem.

2. Burners switching from pre-EPA to EPA stoves reporting new stoves are a piece of s**t, because they won't burn (their unseasoned wood) like the old one did? Would this be because EPA stoves require high temps for efficient burning, and wet wood inhibits that, despite having nearly the same net energy as dry wood?

BTW thanks for sharing my curiosity about all this, and for expressing your interest in public here. May I call you Curious George?

Absolutely. Coincidentally, it's a nickname, and I'm considering changing my name here to that.

Just remember that none of this will rock your world when it comes to actually using your stove when you finally decide which one you want. That's art, not science. Guys like Dennis ("Backwoods Savage") could give two shits about all this stuff, and they burn better and smarter than 95% of the young guys with all the "answers" (Hint: I ain't a young guy). This stuff may help you make the best decision on what stove to buy, or how to install the best chimney (be nice to have Shelton's drafting system, eh?), etc. That's all I hope to do by discussing this all here.

Absolutely! My intent is the same. Paradoxically, a big part of this forum is about learning from the words of people who learned hands-on.

Thanks to this forum I have wood seasoning before buying my stove, and have incorporated innumerable insights into my chimney and hearth design, in hopes of making them efficient, safe, and flexible. I expect to be surprised and challenged when I actually burn, but hope to be better prepared to deal with them because of the words on this forum.

And it's just plain fun for me. As curious person, I look for ways that different disciplines compliment each other, not negate--theory versus practice, science versus spirituality, etc. I see the usual tribal attitude as silly.

Oh, a favorite teaching-riddle on the topic:

Q: What's the difference between theory and practice?
A: In theory, they are the same.

And feel free to blast away at my statements. I'd hate to have erroneous statements or calculations I may make go unchallenged. In fact, I welcome as much fire as you can hit me with. Makes me think harder and staves off the Alzheimer's for a while longer.

Likewise, and thanks again! :thumbsup: