Building my first solar kiln

[etd66ss]

I finally finished the deck, can start framing soon. Having to rip all my lumber on a contractors table saw to get it straight enough to use...



 


 

[etd66ss]

Started on the framing. Sure looks bigger in person than it did on my computer screen...



 


 


 


 


 


 


 

[etd66ss]

A bit more progress, was fighting some gloomy weather until today.



 


 


 


 


 


 

[Nebraska]

Looks good.

[etd66ss]

Just about finished with the framing:



 


 


 

[etd66ss]

I'm trying to get back to this project.

I want to buy the glazing, but a bit confused. The Virginia Tech build uses Tuftex polycarbonate. Home Depot has SunTuf, which looks like the same material: https://www.homedepot.com/p/Suntuf-26-in-x-12-ft-Polycarbonate-Roofing-Panel-in-Clear-101699/100049922

However, I thought I read on these forums that dual wall polycarbonate is needed for moisture? Is that only when used in the winter?

I can't source the dual wall polycarbonate locally, and it's much more expensive than the single wall corrugated.

Does anyone have a good method for doubling up and sealing the corrugated glazing?

[doc henderson]

you could use 6 mil plastic sheeting on the inside.  the more you spend like for uv protected greenhouse plastic the longer it will last.  it is for a thermal barrier airspace to keep in the heat.  the dual wall stuff is more expensive, and can be had at Menards, ect.  after two layers, there is diminishing returns, all well documented.  read the solar kiln paper, and watch the kiln stuff on the NHLA website by Dr. Gene Wengert.

[Larry]

I used the polycarbonate on the outside and on the inside used 6 mil plastic.  UV would make the 6 mill brittle and the air from the fan would crack it.  I think I usually got about 3 years from the 6 mil before have to replace it.  I had this kiln in service for I suppose 12 years or so and it dried 3 or sometimes 4 loads a year.



You can get a glimpse of the 6 mil lining the inside here.


 

[etd66ss]

Will any twinwall work, or is thicker better? I am looking at the 6mm twinwall at ePlastics website (never mind, the shipping alone is almost $700). Menards is not in my area.

A local Lowes has the 6mm twin wall, but only 8 ft lengths.  I have a 50 deg roof due to being up north. This made the panels required 12 ft long, however, that is about 288 sq-ft of solar collector area. Which is ~2800 board feet. I calculate I can load about 1800 board feet into the kiln. So I'm wondering if I can go with the 8 ft glazing even though it doesn't cover the entire roof?  

[doc henderson]

I think it was 1 square foot glazing per 10 board feet to dry.  but less for hard wood like oak, and more for soft wood.  depends on what you will be drying.  I think the 6 mm is the air space.

[etd66ss]

I think it was 1 square foot glazing per 10 board feet to dry.  but less for hard wood like oak, and more for soft wood.  depends on what you will be drying.  I think the 6 mm is the air space.

Yes, 6mm is the air gap, but more gap means more insulation. So was wondering if 6mm is sufficient.
As far as the ratio, yes, it's 10:1 board feet to collection area for 1" thick "lumber". I would be drying primarily spruce & pine for my house build, and then later get into cherry & oak.
It seems the 8ft panels are my only affordable option, so my collection area drops from 288 sq-ft down to 192 sq-ft.
I'm leery of the corrugated + plastic sheet idea in my climate. Seems like I could have moisture issues.

[doc henderson]

Lowes and HD will let you order it and PU for free unless it has changed recently.

[etd66ss]

Lowes and HD will let you order it and PU for free unless it has changed recently.

Yeah, they still don't sell 12 footers. Lowes has the 8 footers in stock, HD only has the corrugated.
I'm taking a look at my design to see if 8ft twinwall will work.

[doc henderson]

I looked several years ago, and you could, but now with supply issues, maybe not.

[btulloh]

There are joining strips available that will work and allow you to use 8' + 4' to make your 12'. 

I got mine from HD, free ship to store making the price very reasonable. 6mm is fine. 

[etd66ss]

There are joining strips available that will work and allow you to use 8' + 4' to make your 12'.

I got mine from HD, free ship to store making the price very reasonable. 6mm is fine.

The H profiles? I figured water would run under the profile if I used that to join seams cross-wise along the roof. I thought those were only to be used along the roof pitch to join.
I got some free used steel:


 
The steel siding wouldn't hold in moisture correct?

[btulloh]

There are some installation docs available for download that show recommended practices for all situations. Very worthwhile to check out. 

[doc henderson]

there is an e-plastics that has them, but shipping may get you.  If you plan to dry some soft wood, then I think you want the largest glazing surface you can get.  

[etd66ss]

there is an e-plastics that has them, but shipping may get you.  If you plan to dry some soft wood, then I think you want the largest glazing surface you can get.  

Yeah, I looked at two places online, over $600 shipping for both, not gonna happen.

[etd66ss]

There are some installation docs available for download that show recommended practices for all situations. Very worthwhile to check out.

OK, so I don't see the instructions showing end to end joining to make a 12ft run out of a 8ft + 4ft. In fact the instructions specifically state the H-profiles are for side to side joining. I assume the panels will leak if joined end to end.

https://us.onduline.com/sites/onduline_us/files/2021-04/Tuftex%20Multiwall%20Installation%20Guide_0.pdf


And the Suntuf instructions state that the aluminum H-profiles are needed outdoors because the plastic H-profiles may leak:

https://polycarbonate.com.au/suntuf-sunlite-twinwall-installation-guide-and-tips/


I assume on the Kilns since the roof is so steep the plastic H-profiles work ok as the water runs down the roof so fast it doesn't have much of a chance to seep in between the H-profile and the twinwall panel?

The instructions also state that 100% silicone can be used, but that it expands at a different rate than the polycarbonate, which can cause leaks.

[etd66ss]

Lowes and HD will let you order it and PU for free unless it has changed recently.

No longer free, Lowes is charging $79 delivery fee (to the store and I still pick up) for both the panels and the H-profiles, so $158 extra right there. Only 8 footers, they don't offer anything longer, likely due to the insane shipping costs these days.

God this economy sucks.

[Nebraska]

I just caught up on this thread. Would you be able build a separate  solar collector infront of /alongside of the kiln you could make up the difference in collector area that way with a little insulated duct to bring the heat in.

[etd66ss]

I just caught up on this thread. Would you be able build a separate  solar collector infront of /alongside of the kiln you could make up the difference in collector area that way with a little insulated duct to bring the heat in.

I think what I am going to do is just go with 8ft x 24 ft of collector as opposed to my original design 12ft x 24ft. A larger portion of the roof will not be glazing as I intended, but I can't justify $2000 in glazing due to a crating fee of $250, and shipping charges of $650. When I can go to a local Lowes and get everything much cheaper.
To me, from reading everything I can about twinwall/multiwall, they are not designed to be butted end to end. That's why they are extruded up to 24ft long...
Ultimately I suppose it means I can't dry as many board feet at one time as I intended.  Unless the volume of air inside the kiln plays a larger role in drying than I am understanding...

[btulloh]

That's pretty much what I did. Sized down a bit so I could use the 8' panels. That makes my ideal capacity 800 bd ft insteadof 1k bf. If you put 1k bf in it just takes a little longer.  For me, the smaller loads are not an issue and using the 8' panels saved a lot of money and/or complexity. 

[etd66ss]

That's pretty much what I did. Sized down a bit so I could use the 8' panels. That makes my ideal capacity 800 bd ft insteadof 1k bf. If you put 1k bf in it just takes a little longer.  For me, the smaller loads are not an issue and using the 8' panels saved a lot of money and/or complexity.

I guess I should have made this decision before I finished the deck & framing:


 
Too late now. Unless there is an air volume issue this is the way I intend to go. I suppose I will have to now insulate the portion of the roof that won't be glazing.