New Solar Kiln - Finishing it up!

[Everest123]

Just finishing up my new solar kiln and thought I would share an update.  It is based on the VA Tech design and it's 20' wide on the outside for an 18' interior dimension.  2" foam board insulation throughout, exterior siding outside, plywood clad inside - painted flat black.  Interior is designed to hold between 1300 - 1600 board feed, depending on how carefully I lay it all out, and I may have slightly overdone the collector area at 198 square feet.  I may have to block some off, or just load up more wood.  Probably fine in the winter, spring, and fall though. I also think I overdid it with the fans.  I put in 4 12" fans, which together pull about 250 watts.  AC power is provided by 800 watts of solar panels feedinge two large deep cycles.  Should be excess power while in full sun.  Thermostat inside plus a speed control will be required to reduce fan speeds which should save even more power hopefully.  I'm guessing in winter, 25% speed will be appropriate, but only testing will tell.

I went with a single good sized side door vs rear sliding doors to save $$.  The extra support structures for massive barn doors was really expensive. So I can't load this with my tractor and forks, but I think it will be okay.  I can position the load with the lumber ends right at the door and just drag them in for stacking.  Plan is to load up two 8' length stacks of two different species to see how they do over a month or two.  Probably some walnut and pine, with the pine being closer to the door as I'm quite sure it will take much longer to dry. 

Any pointers for me as I start to load / run this system?  The adventure continues!!!!

-Jeff



 

 

 

[btulloh]

Looks good.  Better to have too much fan than not enough.  Did you double layer the glazing or is that a single layer?

[GeneWengert-WoodDoc]

Looks like awesome work indeed.  I do believe that double clear sheets for the collector will result in drying about 60% faster...a lot less heat loss through the collector, with a small decrease in solar input, which means shorter drying time as the kiln is more efficient and will run hotter.  Many people use a sheet material inside...it needs to be up stabilized or it will get brittle in a few months.

Fans could be on a timer, starting about two hours after sunrise and off when about two hours after sunset...essentially, the fans run when the kiln is heated warmer than outside.

Generally walnut takes longer to dry than pine...water moves more slowly in walnut plus we target a lower final MC.

[Everest123]

Looks good.  Better to have too much fan than not enough.  Did you double layer the glazing or is that a single layer?

No, it's a single layer of Suntuf Polycarbonate.  I hadn't thought about putting in a top/bottom layer.  That said, I don't think I need / want this kiln to run any hotter.  I measured the interior temp at 4pm on Sunday at 110 degrees, with a 50 degree ambient temp outside.  And that was a 4pm, so the sun was quite low.  The structure is extremely well insulated and we got a little overzealous with the build and made it bigger than the plans.  As a result, there is 198 square feet of collector area, which is more than I originally planned for.  The kiln will practically only hold 1500 b/f max and the collector is sufficient for more than that.  So I'm optimistic that the increased solar energy will counter any loss through the top.  
Anyways, I'm planning to load it up in the next few weeks and I guess we'll find out!!!
My plan now is to load it with two separate stacks of different woods so I can monitor them independently.  Probably maple or cherry, possibly black walnut - and white pine.  I have a LOT of white pine and need siding for a new barn.  So immediate use case for that pine lumber.  I'm so excited to glad my new barn with the lumber from the trees I cut to make way for said barn!!  Bery exciting.
-Jeff

[Everest123]

Looks like awesome work indeed.  I do believe that double clear sheets for the collector will result in drying about 60% faster...a lot less heat loss through the collector, with a small decrease in solar input, which means shorter drying time as the kiln is more efficient and will run hotter.  Many people use a sheet material inside...it needs to be up stabilized or it will get brittle in a few months.

Fans could be on a timer, starting about two hours after sunrise and off when about two hours after sunset...essentially, the fans run when the kiln is heated warmer than outside.

Generally walnut takes longer to dry than pine...water moves more slowly in walnut plus we target a lower final MC.

I thought about using a timer, but also thought maybe I should use a thermostat to just run the fan in the winter when the kiln is over 70-80 degrees inside.  With a full load of lumber there is going to be a LOT of heat stored in that kiln, sufficient to benefit from running a few hours after the sun goes down, I suspect.  Am I overthinking this?  A timer would be a LOT simpler. . . .

[GeneWengert-WoodDoc]

When the kiln is empty, the heat inside is used only to raise the temperature.  When the kiln has wet lumber, the heat is used to evaporate the water...over 50% of the heat is used for evaporation.  So, the temperature will not increase much, unless the fans are off.  In the summer with an empty kiln, it is better to keep the vents open to prevent high heat that can affect fans and even the covering.

The fan times is simple and effective.  It would indeed be better to have a thermostat, but the improvement in drying time would be small, so not worth the effort overall.