The hoophouse would have made a great kiln, still have the materials including the film from it. If I were to build a permanent kiln that's what it would look like (which was the point of the post/pics). Maybe it can help someone who doesn't want to build and take down in a few months. It wouldn't be heated since the boiler isn't used anymore.
Just a quick update, we are having unseasonably hot temps here (almost a 100 degrees with full sun). Temps in the kiln peak (noon to 1300) at >140. I think the temps are higher than that, but my temperature/humidity gauge is digital and the screen keeps going black after 140 degrees. I normally returns to 130 degrees by 1430. In the mornings before the sun comes up the relative humidity peaks out at 90-95% and water drips out constantly until about 9 am when the kiln heats back up.
I experimented with a very small kiln of the same style build several years ago. I used a scale to track the drying of a number of the pieces. It was very easy to see the decreasing rate at which moisture was lost. And I knew to the day when it hit terminal loss. The wood that I had was fresh off the stump, cut and split within a few days. I noticed that my stack of wood that was stacked outside, uncovered, dried at a faster rate than the kiln wrapped wood at first except for one issue, the rain. Every time it rained the uncovered wood took a day or two to get back to where it was. So in the initial stages of drying there was a definite trade off between being wrapped vs the uncovered wood being rained on, rewetting it and having to redry. In the latter stages of drying the kiln wood dried much better than uncovered wood. Both because of no precipitation and the elevated heat. I had temp/RH probes inside and out. I saw the morning RH peak also. The water holding capacity of air doubles every 20 degrees, which is what makes the kilns work so well, even if the RH is 99.9% inside .
I wonder if there’s a limit to how much mass/wood one can wrap and still get acceptable temperatures and drying in the middle? This projects got me thinking again dammit
Yes, there is a limit, but I don’t have any suggestions other than experimenting for finding it. The volume expands as a cubic function, while the area hit by sunlight expands as a squared function.
You do know you lost me when you said there’s a difference between cubes and squares? I did muse on it for a bit and came to the conclusion my first idea, as it was, probably would fail. Maybe a nice hoop house would work tho. I’ll leave it on the back burner for now.
I took your question about a limit to be pondering if there was an ideal dimension to the stack with respect to covering it cheaply while drying the wood quickly. One way to think of it is stacking the wood in a perfect cube (minimal covering). Then think of one side of the cube facing directly at the sun. As your cube gets bigger, the wood at the back gets further and further from the sunlit surface. The sun revolving around the stack does little to mitigate the effect - as the stack gets bigger, the volume of a cube increases more rapidly than the sunlit area increases. A cheap covering and a limited depth to the stack are the answer to larger volumes.
I haven’t done many checks at night, but from what I have seen, the temperature in the kiln will reach ambient by the morning.
Update: I cut back 6 smaller sized trees directly west of the kiln a couple weeks ago. Got ~ 1/2 cord of cottonwood, silver maple, and a tiny bit mulberry. It now gets direct sun until around 1700 so the temps are staying elevated longer. They still peak from noon to 1400 but they stay 30-40 degrees above ambient until 1700. I measured the weights of the fresh cut cottonwood logs I placed in the kiln when stacking it: C1 5.4 lb originally, now 4.2 lb C2 5.4 lb originally, now 3.85 lb T1 9 lb originally, now 6 lb T2 7.8 lb originally, now 5.5 lb K1 7.6 lb originally, now 5.4 lb K2 7.6 lb originally, now 5.1 lb The logs in the kiln (K1/2) and tarp (T1/2) made resounding cracks when tapped so they are either fully dry or close to it. The control logs (C1/2) still made a dull thump noise so they aren’t quite dry yet. I plan on waiting another month and then taking weights a third time. I also may split them then and take mc readings to give definitive numbers.
Cracking is part of the drying process, but not evidence of "being totally dry"...once dry, or at least having reached equilibrium moisture content, the cracks will actually mostly close back up.
I think he was referring to the sound they made when he hit them. A crack sound like good dry firewood makes when you smack two splits together.
It would be interesting if you had an identical pile built next to the kiln and compared the results of the two together.
