New Solar Kiln

[Larry]

I did some trials with fan speed to see if I could improve the drying rate in my solar kiln.  My fan was belt driven so it was easy to alter the speed.  What I found is drying speed increases as air speed increases until a certain point is reached.  After that point is reached higher air speeds do nothing.  I never took the time to measure air flow.  My test results were just by moisture loss each day in my samples.

[Hokiemill]

After only one day it is clear that my vent position was the problem.  I closed the vents to only slightly open and a day later the sample has dropped almost 1 1/2% moisture content.  Learning, learning, learning.

[WDH]

Man, I need one of those.  Figure it all out good so that I can learn from you.....

[tnpete]

Hello I like your solar kiln.
I am trying to decide on one to build. Would like to be able to have the whole back be doors like yours. That way I can take the loader and sit a load of lumber that I would have stacked in the shed air drying. Into the kiln and not have to stack it again.
Think that would work?
Any help anyone can give me toward getting started would be great .
Pete

[Radar67]

Welcome to the forum TNPete. The search feature above will yeild a lot of information on solar kilns. Here is a search I just did...

Use solar for the search string and use Pineywoods for the member. This will gather all the posts by member Pineywoods dealing with solar. He has a lot of info about kilns on here.

Where are you located?

[Hokiemill]

Pete, welcome to the forum!  Those double back doors are perfect for what you want to do.... up to a point.  I think it depends on how long your boards will be.  If they get too long then hanging those doors may become a problem.  I believe that's why the Virginia Tech 2000 bdft kiln uses an end door - more suited to kiln cart and tracks.  For 12' boards or shorter, the back doors will make your loading and unloading easy with the loader.

[JackLeg]

Hello I like your solar kiln.
I am trying to decide on one to build. Would like to be able to have the whole back be doors like yours. That way I can take the loader and sit a load of lumber that I would have stacked in the shed air drying. Into the kiln and not have to stack it again.
Think that would work?
Any help anyone can give me toward getting started would be great .
Pete

Pete:  I built mine with rear doors (like the new VT plan)and I am really pleased with it.  They doors are heavy and do sag some, but, since they are closed most of the time, it hasn't been a problem. 

I just took out my 2nd charge of cypress lumber.  It was 1" boards, 8' long.  It dried to <20% in 10 days of sunshine, which is fine for what we do with it. 

I have a simple Radio Shack Temp/'RH meter in it.  Highest temp I have seen is 136F.  The kiln is doing a great job of reducing our drying times.  Cypress is very forgiving and loses its moisture quickly.  Oak is another matter.

[Hokiemill]

My first load is now officially complete.  The sample board weighs out to 7% moisture content.  The total time to dry from about 48% to 7% was 59 days but a couple factors go into why it took so long.  The main reason is that I was experimenting with the vents and opened them all the way after the load reached about 30% mc.  I thought the open vents would allow more moisture to exit, keep the rh down and allow for faster drying.  Not entirely true.  After noticing the slowdown in drying, I shut the vents to only slightly open and the drying rate increased again.  So having higher temps is better than having greater venting in this case.  With the vents almost completely closed, my maximum temp was 148f.

The other factor that I feel slowed the drying rate was my lack of end baffles.  There was plenty of hot air bypassing my stack by going around the ends.  The next load will include some sort of end baffles but I don't know exactly what to use (a new thread for that question).

The final factor in the long time to dry is that most of the lumber was riftsawn and quarter sawn oak which I understand dries slower than plain sawn.

I'm currently searching for logs so I can mill up my next load.  Once the second load is complete, I'll drop in with another report.

[WDH]

Very interesting.  I await the second load.

[pineywoods]

Hokie, looks like you have come to the same conclusion I did about the venting. Openin the vents to exhaust hot humid air just replaces that air with cool wet air. I finally closed off all vents and stuck a small room de-humidifier in there to take out the moisture. Made a huge difference.