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Solar Kiln Temps

Started by GF, September 17, 2004, 07:30:07 AM

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GF

I am almost finished with my solar kiln, just lack some painting on the outs and some wiring.  I was curious as to what temps are normal, yesturday it was 93 degrees outside inside the kiln at 6' it was 162 degrees, not sure what it was at the 10' top height, also had both 12"x12" vent doors removed at the bottom and temp was still this high.  Is this going to create any problems?  

Den Socling

I know nothing about solar kilns but I know a little about drying wood. A lot of species can't take much more than 100'F when freshly cut unless the humidity is very high. No wet wood could withstand 160 unless humidity was near 100%.

162 is painful. Did you have a thermometer on a 10 foot pole?  ;D

Minnesota_boy

I can't tell you if that will cause problems, but I can tell you that the empty kiln will heat up much quicker and to a higher temperature than a full kiln will.  When you fill it with wet wood, evaporative cooling will reduce the maximum temperature and the volume of wood will take considerable time to come up in temperature.
I eat a high-fiber diet.  Lots of sawdust!

Murf

A neighbour of mine has a solar kiln, he re-did the windows so that he could insert a row or greenhouse windows.

They have a little gadget that looks like a gas spring on a hatchback that expands and it opens the window automatically when the temp. reaches a certain point, then they close again when the temp. drops back down.

They were kinda pricey if you ask me, but then it's all 'mind over matter', if you don't mind, it doesn't matter.
If you're going to break a law..... make sure it's Murphy's Law.

GF

My problem is mind over money, I have something in my mind but it always cost money. :D

Den Socling

Heat alone doesn't hurt green wood if the humidity is very high. If you vent heat, you dump water vapor and this can cause degrade. With DH kilns, you sometimes (with large compressors) have to dump heat (and humidity) to keep the drying process from running out of control.

Murf

From what he tells me he 'adjusted' the opening and closing temp.'s up from what they were.

In his words they don't open at 'August' and close at 'June'  anymore, they open at 'hotter'n'heck' and close at 'tropical rainforest'.

I thought about building one myself, but just to speed up firewood drying, but then again, the 'Honey-Do' list is long enough already.
If you're going to break a law..... make sure it's Murphy's Law.

fencerowphil (Phil L.)

Den,

I realize that it would be easier to get high temps, after a load has been in a solar (or any) kiln, after all the free water is gone.  The total mass being warmed would be drasically less then.   What I wondered about is whether early high temps, without venting much at all,  would kill microbe spores in a wet load?   In other words,   could you use 160deg. to kill all mold and fungus early, so that you could be very flexible with slow-drying species later with no worry.  Does that temp kill spores as well as live organisms?

Phil L.
Bi-VacAtional:  Piano tuner and sawyer.  (Use one to take a vacation from the other.) Have two Stihl 090s, one Stihl 075, Echo CS8000, Echo 346,  two Homely-ite 27AVs, Peterson 10" Swingblade Winch Production Frame, 36" and 54"Alaskan mills, and a sore back.

fstedy

 8) What did you use for a moisture barrier inside and for sealing the inside walls and floor ???
Timberking B-20   Retired and enjoying every minute of it.
Former occupations Electrical Lineman, Airline Pilot, Owner operator of Machine Shop, Slot Machine Technician and Sawmill Operator.
I know its a long story!!!

cozynest

GF...don't worry about that temp. With the kiln loaded and the fans running it will be hard to get it that hot. Besides that's the temp you want to kill bugs and mold.

You didn't say what design solar you have but with mine..( a V tech design) I just follow the formula  Dr. Gene has printed on the wood-web and I have had no problems at all. Now I do air pre dry for about a month or so..so I'm loading the kiln with 60% or so 4/4 wood. I've dryed white oak, cherry, white hickory and tulip popular and all but a very few pieces came out perfect with no weights or binding straps. I've also found using a rual king farm oil based aluminum paint to coat the ends of the wood does just as well as armor seal and is a heck a lot cheaper.

Hopes this helps

Steve
LT27G18; Kubota 3710

GF

Yes it was the V Tech design, once it was filled with a charge the temps really stabalized out.  I have a load of Red Oak in that I put in green off the mill Sept 28th, its down to 8-9% right now, these week long cloudy days are not helping the process any.  

cozynest

Well GF sounds like your doing real good. Your at six weeks with red oak at 8%....now that is really good. With mine I find getting to 12% MC is quite easy...about 3 to 4 weeks....but that last 6 % can take up to 3 to 4 more week for a total of about 8 to 9 weeks for red oak off the mill, and that is in the summer time. That is the reason I partially air dry. I saw more wood than I can dry.. :D so it's always waiting.

Take care and let us know how that load comes out...

Steve
LT27G18; Kubota 3710

GF

These cloudy days are not helping at all, been cloudy and drizzling now for 5 days its expected to clear out friday just in time for more to move in on Saturday.

When I built my kiln, I kinda experimented.  I read an article at one time of you have a floor drain then some dont ventilate, or if you dont have a drain you need to ventilate.

On this load when is was loaded with fresh cut green, I kept the vents closed for the first week.  Water was running off the panels to the front and down the walls to the floor.  When I poured the concrete floor it has 5 layers of vapor barrier and 2" of green insulating foam sandwiched between it and a small taper from front to back to a smal channel troweled in the concrete that tapers to a drain. I had an enormous amount of water running out the drain daily.

Once this kinda mellowed out I went to slow ventilation and have been using it since.  So far I have hardly any warpage or checking, not sure how its going to end up in the end but the lumber looks good right now.  Sure would be nice to see the sun.

GF


GF

I was reading Den earlier reply about wood not withstanding heat over 100 degrees unless humidity was 100%.  

My theory for the drain was exactly that keep humidity at 100% with highest temp possible, letting the water evaporate from the wood and turn back into a liquid form where then the liquid is drained, all this was done without fresh air ventilation, and hopefully minimizing degrade.

Once again I am just experimenting, if nothing else the flat boards will stack nicely into full ricks of firewood. :D

cozynest

GF don't worry about making firewood...it will come out ok....I find it hard to screw up with a solar kiln.

Now I run mine a little differently....when I get surface moisture I open the vents durring the day with fans running and flash off the moisture. then in the evening I close the vents and shut the fans down. By morning I'll be back to 100% humidity and open the vents and start the fans. I weigh samples each day in the evening before I shut the fans down to see what % MC has been reduced. If I see I'm exceeding or near the upper limit of moisture reduction for that species ( 3% per day for red oak) I vent less the next day, and I do this each day until I find a happy medium. If you don't flash off that moisture you will risk staining the wood around the stickers. Wet wood not good.. :D...Once I'm down below 20% I just leave the fans on and cycle the vents open in the morning and closed at night.

Hope this helps

Steve
LT27G18; Kubota 3710

logosoluser

I am about to build the VA Tech design solar kiln. My question is if I am going to have all this moisture running out of my wood do I not need something for a moisture layer? I will be using the plywood bottom, but how is my moisture going to get out of the thing if it seals up as tight as they say it should be sealed? Thanks for the help guys.

cozynest

hey logosoluser guy....I wouldn't worry too much about the water....you only get that wet for a couple weeks or so....consider a fresh cut load weighing 1000 lbs for example. At 100% moisture content you have 500 lbs wood and 500 lbs water. So for each 10% MC you dry down you"ll get about 50 lbs of water or just a little over 6 gals. water. For red oak you shouldn't dry faster than 3.2% per day which would yeild about 2 gals. per day. My kiln is a 1000 bft and I'm estimating a full load is weighing 7,000 lbs so just multiply my exanple by 7, or 14 gals. per day. BTW this fourm has a calculator of weight for most species.  Anyway once your below 60% MC you won't  see as heavy water yield...but a quite moist enviroment non the less.

I just let mine run out the bottom of the load door, although it is weather striped the water still finds it's way out. You could always put in a floor drain but I don't think it's necessary..my opion..just have fun it's a great learning experience.

LT27G18; Kubota 3710

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