Well sometimes you have a project that leads to another project and... this is one of those times. I am a hobby sawer and I saw cherry ,oak ,and what ever else I salvage from my hunting property. Up until now I have been air drying everything. I also need to dry about 400 ft. of pine . So for me I think the best option is a small solar kiln.
I will be framing it out of 1x4 cottonwood ( I have lots of 1x10 sawn) with board and batten siding. The footprint will be 5 x13 so I can dry 12' material. My thoughts were to use 2 insulated sliding glass door panels for the collector.that would give me 39 square feet, so using the 1 to 10 ratio I would be able to dry 390 BFT. I want to hang the black metal roofing panel on the bottom of the rafters and use only 1 box fan to move the air.
I have a few questions ...1) is 8" between the walls and the wood being dried enough for circulation? 2) can I use shiplap cottonwood inside if it is coated with aluminum paint ,or is plywood better?
I am looking forward to feedback from those of you experienced with drying. I will try to post pictures as I progress.
The glass doors may work ok, or may not. Depends on the glass. quality doors use glass designed to block infra-red radiation for efficiency reasons. Cheap glass maybe not so much. Whatever you use needs to be infra-red transparent and treated to resist degrade from ultra-violet. In other words, green house stuff. Green house materials will cost a bit more, but well worth it.
If the glass has a green color or tint when you look at the edge, it is not the best for solar collector covers.
Question #1. I believe 8" is fairly small, but with air dried lumber it will work ok.
Question #2. The interior material is just for protection, assuming you have a vapor barrier under it, and then insulation. So, consider the cost. But, it is important that the exterior have plywood or other material to give rigidity to prevent wracking. In a home, this effect is supplied, for example, by using plywood corner bracing.
Thanks for the input. The glass I have is clear and uncoated.I have been reading as much as I can on this topic,and I thought 2 layers were better than 1 and glass was better than plastic. As far as the 8" space ,I am trying to keep this as small as possible,so a 3' wide stack will dry. Is it better to have more volume inside the kiln? Also do I need the height of a vaulted roof or can I do a gable at 45 degrees front and say 20 on the back to allow for the plenum? I guess it depends on if I need the volume. Thanks !
It is hard to answer your questions, as the kiln design and its function are a system. When you change one, it affects other things.
For example, the roof question...we need 1 sq ft of roof facing south and at about 45 degrees for each 10 BF in the kiln. Sometimes we need more sq ft when drying faster and when needing a whiter color. Also...More volume in the kiln means more heat losses by conduction. So, we try in the proven designs to strike a balance between all the factors to have an efficient kiln. So, it is hard to say if a20 degree back roof is worth the benefit of more space between the wall and lumber.
This is what I have in mind to avoid having a 9' height. This roof design will be about 6'6".
(https://forestryforum.com/gallery/albums/userpics/20947/IMG_0242.jpg)
The ratio is still 1 to 10.
Fine. Another option is to bring the slanted piece straight down from the fan...same energy benefit but somewhat easier to build.
Thanks Gene. I am sure I will hve more questions along the way ,so thanks for sharing your experience.
:P :)
Started the build this weekend. I am building it in my woodshed so it stays dry . I will move it into position just before I mount the glass.
(https://forestryforum.com/gallery/albums/userpics/20947/IMG_0257.jpg)
Well I am finally getting close to completion. One question I stll have is about coating the inside with aluminum paint. From what I read this is used as a vapor barrier. Is this correct ? If so wouldn't that be a double vapor barrier since I used kraft face insulation ? I will try to post some pictures later this week . Thanks for all the help.
Kraft is not usually that good. But, a double vapor barrier should be avoided. This may require slitting the vapor barrier on the insulation
I got the kiln up on my trailer and in position yesterday. All I have left to do is level it and load it. Here are some pictures as promised.
(https://forestryforum.com/gallery/albums/userpics/20947/IMG_0290~0.JPG?easyrotate_cache=1463332145)
(https://forestryforum.com/gallery/albums/userpics/20947/IMG_0291.JPG?easyrotate_cache=1463332213)
(https://forestryforum.com/gallery/albums/userpics/20947/IMG_0292.jpg?easyrotate_cache=1463332315)
(https://forestryforum.com/gallery/albums/userpics/20947/IMG_0295.jpg?easyrotate_cache=1463332639)
(https://forestryforum.com/gallery/albums/userpics/20947/IMG_0296.jpg?easyrotate_cache=1463332800)
(https://forestryforum.com/gallery/albums/userpics/20947/IMG_0297.jpg?easyrotate_cache=1463332875)
Well, that's something you don't see every day, a kiln coming out of a garage. Well done 8)
I like your design in that it will fit best in my limited space. I also like that it can be easily moved.
Outside temp today was only 54 but the kiln reached 157 !
wow. I've never got that good on a hot day here in NC
Nice kiln! Looks sharp and sounds like it works good too. Look forward to hearing how your first load turns out!
8) smiley_clapping nice!
So after 5 days of having a load of pine in the kiln, my high temps have been between 128 and 139 with the fan running. My first temp of 157 was an empty kiln,but my thermometer keeps daily highs and lows ,and the low that day was 33.I drilled my kiln probes for my Ligno DX/C into the edge of one of the boards that read highest with the pins. It was 16 on day one and 11 today. Did I read that pine is done at 9-10 mc ?
I am reading all I can on this topic ,and still have a lot to learn. I think my next load will be some air dried 6/4 soft maple. Thanks Gene and all who share their knowledge on Forestry Forum !
We usually do not dry pine under 10% MC as it gets too brittle when machining, warps more, is harder to nail and staple and screw, and Will probably be around 10% MC in use.
So yesterday I took the wood out because the meter dropped to 9 , but when I checked the surface of the boards it was between 4.6 and 7. I think I screwed up ! Will the boards absorb the moisture from the air to get to 10 percent or do I have to do something to help them?
Yes. It will gradually adjust to whatever the equilibrium moisture level is. Might take a week or 2 depending on "things"
The average RH in your area is about 65% RH, so the surface, if exposed to outside, but not rain, will reach 12% MC in a day or two.
Thanks Ian and Gene. I brought it in and I will be using it this weekend.
Well drying pine went well,as did my second load which was basswood. I think these two species dry easily. I am about to try fresh sawn chestnut oak in 4/4 and 6/4 and I am a little nervous. I don't want to dry it too fast and have it all check. If I run the fan on low and keep the vents mostly closed for a few days will I be ok ? Temps in the kiln are reaching 150 lately. I will keep reading and maybe figure it out.