Solar Kiln Question

[Greg Crawford]

I've done some research on solar kilns, and all the designs I've found use a fan at the top to circulate air down toward the bottom and then out. My idea is to have a chamber at the bottom where most of the heat would be generated, then let the air circulate naturally up through the wood. To get the most equal amount of air to each board, I was thinking I could stack the wood on it's side using dividers between the boards instead of the conventional method of on the face with stickers.

Does anyone have any thoughts, or even better, experience, on whether this would be a decent method?

Thanks.

[Craig Kershaw]

Greg - I took the two day solar kiln course at VA Tech last year. I haven't built one yet but do recall that the professors stressed that the movement of air through the stack of lumber was very important. The other thing that they stressed was that different types of lumber need to dry at different rates so that the quality of the lumber was optimized. The drying of lumber too fast or too slow can result in numerous problems. They had tables for safe drying rates for different species of lumber.
The kiln was in operation while I was there, they had just loaded it with a charge of red oad. Much of the heat generated in the kiln came from a piece of plywood painted black that sat on top of the lumber, its flat side was getting full sun. Interestingly the professors said that they rarely opened the vents, I had the mistaken idea that the vents were left open all the time. They stated that the design of the kiln left enough gaps to let the moisture out and that the moisture in the air in the kiln at the end of the day help relieve the stress that built up in the wood during the days drying.
The guys at Va Tech were very knowledgeable; perhaps you should contact them.

[Ted Jay]

I've done some research on solar kilns, and all the designs I've found use a fan at the top to circulate air down toward the bottom and then out. My idea is to have a chamber at the bottom where most of the heat would be generated, then let the air circulate naturally up through the wood. To get the most equal amount of air to each board, I was thinking I could stack the wood on it's side using dividers between the boards instead of the conventional method of on the face with stickers.

Does anyone have any thoughts, or even better, experience, on whether this would be a decent method?

Thanks.
Greg,
On the Nyle DH Kiln website open this PDF, and save a copy to your computer. It has alot of useful info in it.
http://www.nyle.com/downloads/KilnDrying.pdf
Ted

[Greg Crawford]

Craig,

I did find a wealth of info from VA Tech on the web. I didn't know that the vents remained closed most of the time, however. Thanks.

[Greg Crawford]

Ted,

Thanks for the link. I never knew there were vacuum and dehumidification kilns. From what they said, it sounds like with a small quantity of lumber (about a 4 x 8 kiln), the airflow isn't very critical. It did make me think of a heat source that I have, my AC compressor. Unfortunately, it's on the North side of the house. Good for the electric bill, but bad if I want to use it to supplement the solar energy.

From what I've gleaned so far, it doesn't sound like anyone dries their wood vertically, probably for space considerations. I'm just doing small amounts, so I think I'll give it a try. With the humid conditions I'm in, plus the abundant sun, it sounds like a good combination of heat/moisture to achieve a good rate of drying to maintain quality. I'm going to start with mesquite, which isn't very sensitive anyway, then maybe I'll try some other species and see what I get.

Thanks Again.

[Richard M. Wolfe]

The problem with stacking the wood on edge would be keeping it from twisting and warping. When it dried and shrunk how are you going to maintain pressure on the faces?

The most critical part of drying wood is balancing getting rid of the moisture as quickly as possible while maximizing yield. All kinds of different temperature schedules and treatments are used for different species - misting, steaming, etc. Although I have never used one, solar kilns seem to rely on the night as a critical part of drying to relieve drying stresses in wood.

About anything that is possible to think of in drying wood has been tried too. A company in Germany tried using a huge centrifuge to "spin" the moisture out of wood. Bet that would have been fun to see in operation.