Hawaii Solar Kiln Show and Tell

      A forum member from Hawaii shows his backyard solar drying kiln and gets some advice on improving it. May 27, 2014

Question (WOODWEB Member) :
I just wanted to share a few shots of a small solar kiln I made last summer with the help I got reading a heap of posts and following links from this forum. Thanks to everyone for sharing their knowledge.

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Forum Responses
(Sawing and Drying Forum)
From Contributor Y

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Thanks for posting! Foam insulation? What temperature can it reach? How do you monitor moisture content? I might consider putting stickers a little closer together and arranging boards so that stickers can be lined up straight.

From the original questioner:
No insulation at all. On good sunny days it gets up to the 120ís but usually around 100 with the regular clouds we get here in Hawaii. I monitor MC with a moisture meter with mixed reviews from Amazon but it seems to be close enough for what I am doing which is far from commercial. I am just trying to make use of salvaged wood I come across. I agree the stickers would be better closer was just making do with what I had on hand and all the wood dried well with very little warping. I strapped the stack after the pic was taken.

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From contributor Y:
Aloha Mark. It's a good start. I am sure it will undergo some modification and improvement. Is that mango in there? I am no scientist but here are some quick thoughts. It's vastly oversized for the little bit of lumber in it and the collector to board foot ratio seems it may be unbalanced. A tarp is an easy way to regulate the amount of energy coming in. One centrally located fan is a bit scant. There is a difference from a box that gets hot and dries some wood and a box designed for the even and "controlled" drying of lumber. Though control, can be just a figure of speech when dealing with weather.

The best results are when you can direct the flow of air straight through the stickers and out the other side, up and over the absorber and back through the pile again. This will make the best use of the electricity going to the fans. Ideally if you can have fans the entire length of the stack and the stack baffled to funnel the air so it only draws through the pile that is more efficient and helps maintain a more even drying. You will need to keep the wood out of the sun as well. You can get surface checking, uneven drying on the top of the top layer. Even an upper end moisture meter is only good for 4/4 and still will not represent a moisture gradient in the material properly. On 8/4 the reads 25% still could be 50% in the middle.

You've got the bones of a good system. I have a similar system and itís very low tech. I am in Hawaii as well. I get summer daytime highs of 145 and with overcast days I still can see 110-120. It depends on the rh in the kiln as well. Many people here do not even agree that wood needs to be kilned dried. If youíre on the Big Island you can come over and see what I have. It's not much different but I have an absorber on top of the pile that blocks the sun. The air is drawn across it through the fans then the pile. The absorber is loose ply (see, low tech) painted black. It overhangs the back of the pile and sets on top of the row of fans caulked with an old moving blanket . I also have a 65qt dehumidifier I use to keep night time or during rainy days rh down after the material bottoms out at 9-10%. I find you still need to equalize to 6-7% to make sure all the load is below 9%. For quality woodwork even in the tropics you still need to get below 10%. Either way it's a lot of fun, increases your understanding of the material you use and hopefully creates better material than you were used to using. If you air dry sufficiently it greatly reduces much of the risk of damaging material.

From the original questioner:
Thanks for all the advice. I found out pretty quick I couldn't get the BF I though in there originally and I am using the tarp method you mentioned to remedy that now. I have a plastic curtain I use as a baffle to direct airflow through the stack and keep the wood out of direct sunlight. Yes that is Mango and there is plenty more where it came from. All salvaged from lots being cleared.

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