And yet, another Solar Kiln thread ...

[50 Acre Jim]

Been planning my solar kiln build for some time now.  I’ve read all the threads and watched other members build theirs, so now I should be an expert, right?   But of course, I’m not.  About the only things I’m sure of is I want my kiln to be completely solar powered, handle larger/longer boards, and to convert from an air-drying structure into a solar kiln when the lumber has air-dried to the proper MC.   Here’s what I’ve got so far, complete with (not to scale) images.

As mentioned, the kiln will be completely solar with the fans running on 24-volt DC directly from the solar panels.  I plan on having 2 fans but will adjust that number accordingly as the project matures and I start to get an understanding of what is actually happening in the kiln vs what I think will happen.  The fans I am looking at are called “Solar Direct DC Super Fans”, are 16” in diameter and capable of moving between 1,000 cuft/min on the low setting to 1,900 cuft/min on the high setting.   I plan to let the sun turn the fans on/off simply by when it raises or sets.  If I need to run an exhaust fan after sunset I will run a smaller fan off of a battery bank.  I hope that won’t be necessary as I want to keep this system simple and minimize my daily intervention as much as possible. 

Image 1 is a side view of the kiln.  It will be 16’ wide, 8’ deep and 8’ tall.  The solar heater sits above the main structure and is 4’ tall on the back side and tapers down until it connects with the front of the kiln.    The solar windows on top will be made of Sunlite 24 in. x 96 in. Polycarbonate Clear Twinwall Roof Panel.  (Unless someone has a better suggestion.) 




There will be 4 doors on the kiln, 2 on the front and 2 on the back.  Image 2 and 3 show the kiln without and with doors.    With all 4 doors open, the building becomes a 16’X8’ shelter for lumber to air-dry in.  The location I have chosen has a Southern exposure and sits on the side of a hill with an almost constant breeze that will speed the air-drying process.   When the doors are closed and the solar fans are turned on, the building becomes a solar kiln capable of drying lumber up to 16’ long. 


 


The next images shows the kiln with the movable wall slid into the center of the kiln.  This center wall “parks” against the far-left wall but can be moved accordingly to make 2 separate drying stalls of equal or different sizes.   



Using the movable wall allows both chambers to simultaneously dry different types of lumber or two batches that are started at different times, say a couple of weeks apart from each other.   It also allows for lumber to be air-dried on one side will kiln drying lumber on the other. 





I spent the last couple of days cutting a pad, driveway and turnaround for the kiln.  Wanted to finish it off and start construction today but 6+ inches of snows says otherwise.   

So there it is guys.  Look it over and give my you ideas, criticisms, suggestions, etc.    Thanks in advance,

Note: Since I made these drawings I have decided to put the solar panel(s) on a separate, free standing support and not take up space on the kiln itself.   No sense in wasting all that solar exposure, right? 

Jim

[CharlieP]

Hey neighbor, we are over in Stecoah, off 28, I built a solar kiln this fall based on VA Tech plans, you are welcome to come over and check it out , I would be glad to go over some things I have run into.
  Charlie

[WLC]

IF you are gonna dry 16' lumber your kiln will need to be longer.  I'll be watching as you build this.  Very interested in how it turns out!

[50 Acre Jim]

Maybe I can find a market for 15’11” lumber?     Or better, I’ll probably end up with a 2X4 on each side to increase the width a bit.     

I think the greater problem here is that the solar collector is not at 45*.  Is that serious enough that I need to raise the back wall of the collector from 4’ to 8’ or will I catch sufficient sun at the current angle?

[GeneWengert-WoodDoc]

The angle is a big issue, with a big effect from September through March.  You will recover as much as 15% less energy.  The best angle is your latitude, so 45 degrees is too steep for your location.

Are the walls 6” thick? Doors too?  Floor insulated also?

I am not sure why there is so much space from the top of the pile to the horizontal baffle.

Will the fans blow downward?  Will the vents have adjustable covers?

[50 Acre Jim]

The angle is a big issue, with a big effect from September through March.  You will recover as much as 15% less energy.  The best angle is your latitude, so 45 degrees is too steep for your location.

Are the walls 6” thick? Doors too?  Floor insulated also?

I am not sure why there is so much space from the top of the pile to the horizontal baffle.

Will the fans blow downward?  Will the vents have adjustable covers?

Latitude/Slope of panels: Latitude for Franklin NC (I'm 15 miles West of Franklin) is 35.1823° N and the slope on the collector is currently at 23*.   I can change the degree of slope by making the back of the collector a little higher.  It's 4' now, raising it to 5', or possibly 6', should help considerably.

Wall thickness: Walls will be true 2X6 construction as I am cutting the lumber myself.   

Floors: Floors will sit on 4X6 beams that rest on pier blocks.  I will insulate the area between the beams and cover that with a couple layers of 30lb felt.  Then cover that with 1/2" plywood. 

Baffle: The drawing is to not to scale.  It's only purpose is to provide a mental projection of what the design looks like.  Anything and everything is subject to (and most likely will) change.  With that in mind, the positioning of the baffels in the diagram is there only for you to see that there is a baffle and the approximate location. 

Fans: Currently I plan on 2 fans, one on each side of the kiln.  And yes, they point down as they pull the hot air from the top of the kiln and direct it down into the drying chamber.  These are very powerfull fans, I don't expect there will be an issue with too little air movement.  If anything, there may be too much, if that is possible. 

Vents: Yes, all the vents will have adjustbable covers. 

Thank you for your input/questions Gene.  Any suggestions are appreciated. 

[scsmith42]

Jim, if you're headed to Raleigh any time soon you're welcome to stop by and look at my 4 solar kilns.  One is the traditional design and three are modified to better fit my standard kiln stacks.

[Savannahdan]

I notice that your vents are in the sides of the front chamber.  Wouldn't it be better to have them in the back so that the air flow through the stacks is constant and you're pulling fresh air in.  I do like your 2 chamber system.

[50 Acre Jim]

I notice that your vents are in the sides of the front chamber.  Wouldn't it be better to have them in the back so that the air flow through the stacks is constant and you're pulling fresh air in.

I'm pulling a regulated supply of fresh air in from the front so that it is introduced into the lowest part of the heating chamber, where it is warmed as it rises.   I'm hoping this will ensure that the hottest air possible is being pulled out by the fan and forced down through the stack.       



If the vent were in the back the forced hot air would be exiting prior to going through the stack.  By putting the vent in the bottom front, I am allowing wet (heaver) air to vent that has already been forced through the stack. 

I do like your 2 chamber system.

Thank you!

[GeneWengert-WoodDoc]

I do,believe the vents are ok, but if you could move the two front ones closer to the center, this would help air movement side to side.

[50 Acre Jim]

I do,believe the vents are ok, but if you could move the two front ones closer to the center, this would help air movement side to side.

I'll make those changes in the final build.  Thank you!

Edit:  Sorry Gene, I just saw what you meant about the baffle being so far back in the picture on the stack.  Fixed it!  Also moved vents from side to front and extended the back of the solar collector to 5', which should bring the pitch of the collector to 32*.  Optimum is 35*.  Jim

Edit #2 - 12/12/2017: Although it is not noted in the image below, I have changed the back wall to be 5'6" high, which will make the pitch of the solar collectors exactly 35*.  Life is good...

[Savannahdan]

Ok, the airflow diagram helps. 

[50 Acre Jim]

I’m about 99% finished cutting out the pad that the kiln will sit on.  I made it 50’ X 95’ which will give me plenty of room to add another kiln if this design works out well.  I wanted to be sure I have enough room to load/unload lumber as well as being able to turn a truck or tractor around without running into anything.  It was 15* this morning with a steady wind that made it hard to see through the tears!  I have a little bit of grading to do to insure the water drains in the right direction and then I’ll be ready to start laying out the blocks for the kiln to sit on.



Got a partial cut list made.  I will have to buy the plywood, but I have enough stock to cut everything else.  Also got my solar fans ordered.  Depending on the amount of sunlight hitting the panel at any given time each fan will move between 1,000 - 2,000 cuft/min.  If that isn't adequate I'll add a third fan but I think with the amount of sun that hits this area I will see them turning at the 2,000 cuft/min speed more than not.   Pricey little rascals at $239.00 apiece, but anything "solar" seems to cost twice as much. 

 

[GeneWengert-WoodDoc]

Cheap fans are not as efficient and use brass bushings or worse.  Your fans will last forever and the cost of running them will be good.

Sometimes, using this area to air dry is good, plus if you had a pole shed with only a roof, no walls, you can work in any weather...put that on your Christmas wish list.

[Crusarius]

I am so in for this build. Me likey so far.

[50 Acre Jim]

Cheap fans are not as efficient and use brass bushings or worse.  Your fans will last forever and the cost of running them will be good.

 
Good to know!  I feel a little better about the purchase now. 

The good news: Got all 19 of my 2x6x12 rafters cut today.  They sure are purdy!
The bad news: Got 80 more 2x6x8 to go! 

[SlowJoeCrow]

I like your design - it has a lot of flexibility.

[50 Acre Jim]

In spite of snow, ice, and rain I managed to cut 30 - 2x6x8 today.  Only 50 more to go and I will have enough framing lumber for the walls.  Then I'll move on to the 4x6's for the floor and the single 4x12x18 that will span the front, hold the walls together and support the 2x6x12 rafters that the polycarbonate panels will rest on.  And then, I will visit Lowes to buy some 3/4" plywood for the floors and walls.   My plan is to use plywood on the walls and then cover the outside with lap siding that I make from White Oak. 

Lot's more to do but so far I'm having a good time!   

[WLC]

Off topic of your kiln, which I am definitely excited to follow, but had a question.  Ever still find any chestnut logs in the creeks around your parts?  Been 25 years ago, but helped pull a couple of logs out of a creek down towards Franklin.  Made some nice wormy lumber.  Still have a picture frame out of it.

[GeneWengert-WoodDoc]

The original Virginia Tech design used CD-X plywood.  You might have to replace a sheet or two in a year or two, but the cost is good.