Getting ready to build a Passive Dry Kiln off grid

[just_sawing]

I have been working up designs that use no electricity. On my farm I can sacrifice some time and a slower drying schedule for not having to run electricity where I want the kiln.

 

This design uses a baffle to draw heat at the top through the wood and pull out the back. It is designed that I can add fans but I am trying not to.
Now for the second part. Since I run RR ties I have a lot of pallet wood that is currently .20 on the market. I am thinking of building this kiln by laminating 4 inch wide boards on top of each other building solid walls (Inside wall also) this will give a thermal mass to aid drying. Have any of you ever used log construction for kilns?

[Planman1954]

I like the idea of what you want to do, but I'm not sure about the thermal mass ideas. I want to build a passive solar greenhouse next year, and so I've looked at quite a few design ideas. The idea of the thermal mass is to keep the heat collected during the day inside the mass which is then released at night back into the confined area. Most of the thermal mass I've seen is masonry (rocks) or water inside barrels. Water is the best medium for heat storage, from what I have read. I'm not sure that wood is your best retainer for heat storage. Having said that, why would you want to retain the heat at night anyway? I think that having the wood relax at night helps in providing a more stable end product (from what I've gathered here at the forum with solar dry kilns.)
This leads back to your basic design. I'm thinking out loud here. First you need a large south facing glazing. I know that you can buy an insulated plastic used in greenhouses which would let the rays in and keep the air inside better. I would then heavily insulate all the remaining walls and seal all areas for air leaks. I would want an easy access on the north wall to load and unload lumber so that I would NOT have to bend over lifting! I would use a concrete floor with a .006 mil poly underlayment to prevent ground moisture (mass, remember?) I'll bet if you leave the lumber in there for a couple of months, the moisture content would lower quite a bit, and you would be good to go. Just some thoughts...

[GeneWengert-WoodDoc]

I agree with Planerman especially regarding a heat sink...I ask why store the heat instead of using it all when it first comes in?  I also like the evening rest period with high RH to relieve stress.

I also wonder how the hot air on the top can be forced through the lumber pile.  It would seem that it would just get hotter and hotter at the top.  Can you give more info on how that will work?

[just_sawing]

The top of the stack is open to the back side. The top has plastic on it also so it will heat. THe front is isolated from the rear except where it down drafts to the base of the stack. Being hot it rises at the rear of the stack and is drawn through to the vent. 


  

I am thinking that having the solar heat at the top will help the drafting. The reason behind the heat sink is to be gentle. The mass will cool down slowly and heat up the same this allows a more gentle relaxation and better quality.

[wolf nemeth]

 I like the bafles, but  wonder abut al that therma mass...but if you do build it, I'd like to come see. I am  near Liberty, so we can't be too far apart. Where are you?
Wolf

[GeneWengert-WoodDoc]

After the air goes through the stack, it will be cooler and want to sink to the bottom.  So, you will need a stronger force to make it want to rise and exit.  I think you need a vent on the bottom, not the top.

But, if the wind is blowing, that will be stronger than the slight movement caused by heating. 

The heat sink will make the temperature rise even smaller. 

But even if you do get a lot of heating, what will make the hot air sink and go down to back of the sink to the bottom of the pile?  I think the hot air will just get hotter and stagnate in the front.

I hate to be so negative, but I am concerned that you will have a mold factory and not a dryer.  This design, using fans, is sometimes called a single pass dryer in that the air makes one pass through the dryer and then exits.  We sometimes like a re-circulation dryer so that only a little air is exhausted and the rest, with its heat, goes through the pile again.

[Ianab]

Have you seen Bill's off grid solar kiln? A couple of small attic fans and matching solar panels. You only need fans when the sun is shining.

https://forestryforum.com/board/index.php/topic,73428.0.html

[just_sawing]

First of all that is my concern about the stagnant air. If the top compartment about the wood can't get warm enough to draft it will be stagnant. If that happens Solar panels will be installed. As the air wants to be cooled it will also cool the bottom of the wood stack which makes (I hope) circulation to the front.
I am in the middle of remodeling the old Buck Smithson house which is behind the Liberty Mule for those who are familiar with Liberty TN.


 

[Bill Gaiche]

Thats a pretty cool house. Keep us posted on the progress. bg

[pineywoods]

I think wood doc got it right. Mold factory..Physics 101, hot air rises, cooler air sinks..Think You will find you don't need the thermal mass. A stack of wet wood will hold a lot of heat..