# Solar Kiln - how about Solar Fans?



## dnyelator (Sep 10, 2009)

My son built a solar kiln out of a book he bought that is about 5'w x 8'L x 7' tall in the back. It has a 45 degree sloped roof that is plexiglas. It's getting nice and warm in there, but we need to get the air circulating, and I'm leary about running electricity out there, so I was thinking of hooking up a couple of computer fans to a couple of solar panels. Was wondering if anyone has tried this before and if you think it will move enough air? There are some pretty decent velocity fans on the market for $10-20 but not sure they will cut it. Any help is appreciated. I don't post much, but I read alot of your comments. This forum is amazing.

Dale in NE


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## joecool85 (Sep 10, 2009)

dnyelator said:


> My son built a solar kiln out of a book he bought that is about 5'w x 8'L x 7' tall in the back. It has a 45 degree sloped roof that is plexiglas. It's getting nice and warm in there, but we need to get the air circulating, and I'm leary about running electricity out there, so I was thinking of hooking up a couple of computer fans to a couple of solar panels. Was wondering if anyone has tried this before and if you think it will move enough air? There are some pretty decent velocity fans on the market for $10-20 but not sure they will cut it. Any help is appreciated. I don't post much, but I read alot of your comments. This forum is amazing.
> 
> Dale in NE



If you get 100+ cfm then you will be good to go, should make a nice difference getting the very humid air out of your solar kiln. Of course it depends on the size of your kiln. I'd say for a 10' x 5' x 5' tall kiln you'd be good with one fan.


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## redprospector (Sep 10, 2009)

I don't think they will move enough air for a kiln of any size.

Andy


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## fubar2 (Sep 10, 2009)

Take this for what its worth which is probably nothing. I would try small doors around the bottom I could close and put in a chimney. Who knows natural convection might work. Sure wouldn't hurt.


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## Ted J (Sep 10, 2009)

Here is some additional info... WARNING.... you could get lost in all the info and overload!!! HEHEHE  

http://www.builditsolar.com/Projects/WoodDrying/wood_kiln.htm

http://www.dnr.state.wi.us/forestry/um/hobbyist.htm

More INFO


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## dnyelator (Sep 10, 2009)

Thanks for the replies folks, now I'm not sure what to do  Ted - you are right, just need to know where to look to get the info. I looked around alot trying to find info, but didn't come across the sites you recommended. Thank you very much!

Dale


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## Ted J (Sep 11, 2009)

dnyelator said:


> Thanks for the replies folks, now I'm not sure what to do  Ted - you are right, just need to know where to look to get the info. I looked around alot trying to find info, but didn't come across the sites you recommended. Thank you very much!
> 
> Dale



Glad to help Dale.
Got to thinking about it a bit more, about the air circulation, an option for fans might be the dual electric radiator cooling fans, or maybe a single fan. The fans do circulate alot of air and just might be the right fit for what you need. If you add a Temp Control W/ Relay Switch to it so it's not on continuously, that will give the solar panel time to charge a 12v battery. You could also have it run the fan only and eliminate the battery, no sun no fan.


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## Fallguy1960 (Sep 12, 2009)

A Friend of mine dried his logs for a log home by piling them in a pyramid shape and covered them with black plastic. The pile was on a slight hill. When the sun was bright you could watch the plastic that was over the high end of the pile float on the hot air coming out from under the plastic. I would try a low and high vent hole first and if needed put a fan in the bottom hole to increase the air flow if needed.


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## redprospector (Sep 12, 2009)

I've built a few kilns in my time, and through trial and error and some good advice from a kiln operator I learned a few things. (This was before I owned a computer.)
The air flow needs to be constant to carry moisture out from between the boards, and the temperature needs to be consistant or the quality of your lumber, and the time it takes to dry it will suffer.
The trick to a solar kiln is keeping the temp constant. You may need something more than the plexiglass roof, like lava rock or something to help hold the heat overnight.
The radiator cooling fans might be the trick for circulation if you can keep the battery charged with solar.
On a solar kiln you also need to make the roof to where the condensation can run out of the kiln or you'll have to use a de-humidifier.

Andy


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## dnyelator (Sep 13, 2009)

*lava rock*

Red - so how much lava rock are we talking for a kiln my size? I also thought with vents in the top and bottom and a couple of fans that I could get the moisture moving out of it, but you mentioned making the roof where condensation can "run out" of the roof. Ours is pretty much sealed up except for the vents, so we may have to rethink that I guess. This is turning out to be alot harder than we first thought and certinaly more complicated than the simple plans we worked off of.


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## BobL (Sep 13, 2009)

redprospector said:


> The trick to a solar kiln is keeping the temp constant.



This depends on the temp range the solar kiln is operating over and the type of lumber being dried. In hotter climates like Australia it is actually an advantage to have a moderately variable temperature range. Large size Aussie hardwood lumber dries with less warping and shrinkage if the temperature is allowed to vary over a 24 hour cycle. Solar Kilns in hotter climates tend to draw out too much moisture too quickly during the daytime so it is better to let the timber cool off a little overnight so some of the moisture from the inside the timber can move towards the outside. If too high a constant temperature is used, hardwoods especially can develop a high internal moisture gradient which can damage the timber.

If there is enough lumber in the kiln the lumber itself can act as enough of an overnight heat sink. Of course adding more heat sinking will help. I am surprised that (closed) water tanks are not used because water can store a lot more (4 times) heat than rocks.

I agree with the need for some circulation otherwise the drying becomes very uneven and the lumber can develop mould. The sort of recirculation figures quoted in commercial kilns are air velocities *through the lumber stacks * of 200 feet per minute (1 m/s). This needs a 1 - 2 HP motor so you can chew a fair bit of electrical power and $ in drying. Of course this can be scaled down and it just takes longer but if there is no recirculation and poor moisture release you can just end up breeding mould.


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## redprospector (Sep 13, 2009)

dnyelator said:


> Red - so how much lava rock are we talking for a kiln my size? I also thought with vents in the top and bottom and a couple of fans that I could get the moisture moving out of it, but you mentioned making the roof where condensation can "run out" of the roof. Ours is pretty much sealed up except for the vents, so we may have to rethink that I guess. This is turning out to be alot harder than we first thought and certinaly more complicated than the simple plans we worked off of.



The last solar kiln I built was different than what you built. The lava rock's might be a pain in the butt on your's, but on a 5' x 8' if you put it 3" or 4" deep on the floor it should hold the temp overnight. My problem with this style of kiln has alway's been overheating in the mid day.

The last one I built had the solar collector seperate from the actual kiln, they were connected, but seperate room's. The collector was on the South side, and I had about a foot of lava rock in the bottom of it. I had 2 fan's through the wall between the collector, and the drying room. I hired a HVAC guy to set the fans up to where they would come on when the temp dropped below 110 degrees, and off at 120 (I don't understand all I know about that set up).
The temp in the collector would reach about 160 to 170 on a good hot day, and the lava would hold it well enough to maintain temp for a couple of cloudy day's. The circulation fan's were in the top of the drying room, with a curtain (tarp) that would roll down to the top of the lumber stack so the air had to circulate through the stickered wood. It wasn't total solar, but it saved a lot of money on propane. Would hold right at 2000 bd ft of lumber, and would dry 2000 ft of Pine post haste.

Edit: When I mentioned the temp reaching 160 to 170 on a good hot day, keep in mind that if it hit's 80 in mid June we consider it damn hot here.

Andy


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## redprospector (Sep 13, 2009)

dnyelator said:


> Red - so how much lava rock are we talking for a kiln my size? I also thought with vents in the top and bottom and a couple of fans that I could get the moisture moving out of it, but you mentioned making the roof where condensation can "run out" of the roof. Ours is pretty much sealed up except for the vents, so we may have to rethink that I guess. This is turning out to be alot harder than we first thought and certinaly more complicated than the simple plans we worked off of.



:bang: I forgot to give my opinion on the vent's.
Try it, they may work and work well.
The kiln's I built similar to yours I didn't put vent's in. I used the corrugated fiberglass pannels (clear) for the roof, and left it unsealed at the eave. The first few day's of a new load, it would look like we were having a light rain judging by the water dripping off the roof.

Andy


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## dnyelator (Sep 14, 2009)

redprospector said:


> :bang: I forgot to give my opinion on the vent's.
> Try it, they may work and work well.
> The kiln's I built similar to yours I didn't put vent's in. I used the corrugated fiberglass pannels (clear) for the roof, and left it unsealed at the eave. The first few day's of a new load, it would look like we were having a light rain judging by the water dripping off the roof.
> 
> Andy



Thanks Andy, wish I had thought of that. I guess we're sort of stuck with our design now. Going to put two more vents in and a couple of small circulation fans and see how it does. It's not getting alot of sun is the main problem right now. The neighbors tree is blocking most of the PM sun, so we may need to move this out to my brothers place, but I want to get it running correctly first. Also thanks BobL, you guys have alot harder wood where you are at than we do. We usually cut and air dry our lumber for a couple of months and then finish it in the kiln, so molding hopefully is not a problem. Thanks again for all the tips everyone. I have some things to try. You guys are great!


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## BlueRidgeMark (Sep 14, 2009)

Vents at the top, vents at the bottom, and convection will move a lot of air.


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