Pre-build solar kiln questions(Photos of kiln building progress)

[caveman]

What is the best way to seal the ends of the collector on the corrugated polycarbonate roofing material?  Do you add foam that fits betweenthe corrugations and the header?   Second, when following Pineywood's design, where and how are the fans mounted?
Thank you,
Caveman

[pineywoods]

The box stores where you will probably get your glazing will have strips of 1X2 cut to fit the corrugations. the fans are mounted up near the top blowing downward. You need a baffle to force the air to make a 90 deg turn and flow through the stack. I use a chunk of old canvas tarp hung from the fan supports and hanging down to the top of the lumber stack.

[Planman1954]

Take a look at "Solar Dry Kiln Construction" thread. I have photos covering the build start to finish.

[caveman]

Thank you both.  I will try to get JMoore to take some pictures.  We are building the kiln on an old trailer house frame that is about 28' long.  We are going to make the kiln 20'x7'.  The remainder of the trailer  will be used for storage (stickers and stuff).  We will support the trailer frame before we load it with wood.
Caveman

[Planman1954]

Hey Caveman...Take lots of photos! It helps others here get inspired by the work.

[caveman]

JMoore took some photos today.  We did not get too much done this morning due to the rain.  We did cut and drill some brackets that will be used to mount the cross members that will span the trailer. 

Planman, when looking through photos of your kiln build, I could not tell if you insulated the floor.  If you did not, is there a reason we should not?  We were planning on using visqueen as a vapor barrier with insulation on top of it below the floor.
Caveman

[Planman1954]

Heat rises. I did not think it super important to insulate the floor joists. Of course, it might increase the inside temperature when the kiln is in operation, but I think not very much. I DID use felt to provide a vapor barrier under the floor boards however. I think there are photos of me doing that.
Remember, though that the kiln has reached temps over 180 d. farenheit here in Louisiana. It will dry pine down to 12% in 5 days, and down to 6-8% in another week.

[caveman]

We may forego the under floor insulation.  I think it would be a great place to raise rats and other vermin.  Skipping the under floor insulation will simplify the build. We got the axles mounted today, welded a new tongue on the trailer, and cut and mounted some 4"x6" ash beams to use as floor joists.  JMoore took pictures on his phone.  If he posts them to my gallery, I will show what we have completed.
Caveman 

[GeneWengert-WoodDoc]

If the fan is blowing the air around, then insulate the floor.  The fan cancels the idea that heat rises.  The more insulation, the less building heat losses and the more heat energy available for drying.

[caveman]

 The first photo shows the abandoned trailer frame that we hauled home. Afterwards, we cut the spring hangers and axles loose.  Some of the springs had rusted in two.  The frame is pretty solid 6" channel.
 

 

[caveman]

  

  The trailer has had the springs and hangers removed.  Cradles for the axles were made out of 3"x6" tubing, axles were flipped over, some used tires and wheels were added (center holes of wheels were 1/8" too small for hubs), and some of the rust was brushed off.  This trailer will not be used on the road.  

   
After the trailer was turned back over, the angle iron brackets for the joists were welded on.  

   
The joists are secured to the trailer.  Soon we will have to get started on the kiln part of this project.  

 
My dad helped Jmoore and me some today and yesterday.  

[pineywoods]

If you are concerned about excessive heat loss, there are 2 options.
More /better insulation and double layer glazing.
Or you can just turn up the heat. That's the purpose of the black sheet metal on the bottom of the rafters..Try it, you'll like it 

[caveman]

We are planning our build based on your plans and Planman's pictures.  It is usually pretty warm here.  The daytime highs have been close to 80° and lows in the 60°'s this week--yesterday afternoon, we were swatting mosquitos. 

I wonder if the polyethylene film used on green houses would stand up to the heat produced inside the kiln?  On the green house at school, the top has two layers of plastic that have a small fan pushing air in between.  This air envelope provides some degree of insulation.  If it would hold up, we could use the clear corrugated panels for the top, poly film under the rafters up to the fan attic/heat collector and mount black metal to thin strips below it all.

If, after using the kiln, we need to contain more heat, we could go underneath and insulate it.  After we build this contraption, I need to find a sunny spot that is not in my front yard that is within reach of a power cord.  We may just have to make a sunny spot.
Thanks for the guidance.
Caveman

[thecfarm]

Greenhouse plastic might work,I have no idea. But be forewarned that greenhouse plastic will start to break down after what ever the manufacturer says to replace it. When we had ours it would only last 4-5 years. May still look good,but it won't let as much sunlight through it.

[caveman]

That is a good point about the reduced transparency of the plastic over time.  We will build it first without it and if it does not get hot enough inside we may experiment with it.  I guess we could put a small piece of the poly film between the black metal collector and the clear corrugated panels and see if it melts.  If it turns to goo we will know not to use it.
Caveman

[GeneWengert-WoodDoc]

It is good to appreciate that the amount of energy into the kiln is the same if the collector is right under the glazing or many feet away.  It is the solar shadow that determines the input.  (I recall one kiln that used a corrugated collector supposedly to increase the energy input.  But it is the amount of energy entering the kiln through the glazing that is the key, not the absorber area.)  If the inside of the kiln is black, then 100% of the incoming energy will be absorbed and converted to heat.

If the kiln is well insulated, then the major heat loss will be through the vents (so do not over vent) and through the collector's glazing by convection to the outside and radiation.  Radiation and convection losses are reduced if the absorber is further away for the collector.  Two layers of glazing improve efficiency by almost 50% faster drying.

[wolf nemeth]

 Two questions---
   If you have  an insulated floor, you have mice and rats. What do kiln users do about this?
   I would like to build my kiln where there is no electricity. Would a couple of the solar powered vent fans that are used on boats  (like Nicrovent, or similar  items sold on Ebay)) provide  adequate venting for a kiln built to dry a 5'x12' stack of  lumber? They are rated to move appx 100 cu.ft/hr, and some even run on rechargeable battery power for  several hours after sundown...

[Planman1954]

I've never had any problems with rodents. There are trade offs in life, and this seems to be one of them! I chose no insulation in the floor, and have had no problems. (And I still have a kiln that reaches temperatures over 180 degress.) I DID insulate the walls, however.

[GeneWengert-WoodDoc]

You need fans to circulate the air in the kiln through the lumber pile.  Vent fans are not needed.  The cfm is calculated.  For example, with 12' long lumber, 20 layers, 3/4" sticker space (0.75 / 12 feet) and 100 fpm velocity required, then cfm = (0.75 / 12) x  12 x20 x 100 = 1500 cfm.  Add maybe 25% - 30% for leaks.

[GeneWengert-WoodDoc]

In the VA Tech kiln that I developed, we put metal hardware cloth on one kiln on the bottom, which kept the rodents out, but the insulation was exposed to the ground moisture.On another we put plywood on the bottom of the floor joist and then insulation, then plastic on the warm side only, and then a layer of plywood on the top of the floor.