Building my first solar kiln

[etd66ss]

Of my 4 solar kilns, three use double pane polycarb panels designed for green houses (greenhousemegastore.com), and one uses a single pane polycarb similar to what you're looking at from the Home Supply store.

I can effectively dry for 2 -3 months more a year with the double pane kilns versus the single pane.  They have the advantage of having closed cell spray foam insulation too though.

About 10 years ago one of our FF members did an analysis of the effectiveness of drying with a double pane glass versus a single pane. It was quite informative in terms of the benefits of the better insulated panel.

https://forestryforum.com/board/index.php?topic=84982.msg1302695#msg1302695

I've had zero issues with moisture in mine.

Did you use the 6mm twinwall polycarbonate or thicker?
I think I would have condensation issues being up in the northeast right near the Great Lakes.

I used 8mm. The ends of the panels are not exposed to the inside of the kiln, and have air exposure at top and bottom.

So you didn't use any of the u-channel trim or aluminum tape?

[farmfromkansas]

I used the twinwall panels from Menards, and bought the joining strips to put them together, then needed a bit more on the edges, so just put a joining strip on both edges.  Used their glazing fasteners along each edge, after putting some clear silicone in the strip to make things hold, and be water tight. My kiln is exactly 16' framing, plus the boxing and siding, so it turned out to be about 16'-3" total. The joining strips added enough so I had about 1" overhang.

[scsmith42]

Of my 4 solar kilns, three use double pane polycarb panels designed for green houses (greenhousemegastore.com), and one uses a single pane polycarb similar to what you're looking at from the Home Supply store.

I can effectively dry for 2 -3 months more a year with the double pane kilns versus the single pane.  They have the advantage of having closed cell spray foam insulation too though.

About 10 years ago one of our FF members did an analysis of the effectiveness of drying with a double pane glass versus a single pane. It was quite informative in terms of the benefits of the better insulated panel.

https://forestryforum.com/board/index.php?topic=84982.msg1302695#msg1302695

I've had zero issues with moisture in mine.

Did you use the 6mm twinwall polycarbonate or thicker?
I think I would have condensation issues being up in the northeast right near the Great Lakes.

I used 8mm. The ends of the panels are not exposed to the inside of the kiln, and have air exposure at top and bottom.

So you didn't use any of the u-channel trim or aluminum tape?

I used u channel in-between the sheets and flashing at the top. The bottom is open.

[caveman]

.  I'll lift the center doors off with my TLB bucket.

This is what we did.  We will not do our next kiln that way.  It is difficult to get centered just right and with our sandy soil it is difficult to keep it on the same plane as the opening when trying to install the center panel.  

 

Another thing we will do on our next kiln is similar to the way we did our hot box.  We cut utility poles flat on two sides at 11" and built the structure on top of them.  It is easier to hand load than the one pictured is on those occasions when we need to hand load.

Another thing we will do on the next one is hinge the doors from the corners or load from the end on a cart.  The drawback to the cart is that it would take up drying space.

[etd66ss]

My first design was to load from the end on rails/cart. But I eventually decided doors in the back would work best for me.

[etd66ss]

For those that used the twinwall glazing with the H profiles. Are the panels exactly 48" wide, meaning center to center spacing of H-Profiles is more than 48" if you don't trim the panels on the long edge? Seems like that would be a PITA for 24" rafter spacing...

[scsmith42]

For those that used the twinwall glazing with the H profiles. Are the panels exactly 48" wide, meaning center to center spacing of H-Profiles is more than 48" if you don't trim the panels on the long edge? Seems like that would be a PITA for 24" rafter spacing...

I did not have any problems with installation. I think that the panels are 1/8" under to allow for the h profiles.

[doc henderson]

the strips that i think you are calling H strips on the Menards web page, seem to have a extra space in the center.  might be able to get tech drawing to see.  but it would grow a bit, if not compensated in the panel size.  best to get the panels before the build maybe.

[btulloh]

There are several good documents out there (google) about installation, not all from the same manufacturer, although it's the same product no matter who made it.  I found it very useful to read their docs.  The recommended fastening pattern is much different than what I would have expected.  Plus these docs have a lot of technical info that's good to know before hand.  I'm going to try and attach one or all of them, but some are pretty big files and I think there's a size limit of attachments.

One very important thing is the recommended spacing for the blocking or horizontal support members.  They recommend 24" max, although mine is closer to 30" and no issues (with the steeper angle, it's less of a problem.  It's also important to allow room for thermal expansion in the panels.  It doesn't take a lot, but it will keep them from buckling.  This is accomplished by using their fasteners, which self-drill the correct clearance at the fastener location.  Also not trapping the edges and leaving a slight gap between the panel edge and the h-strip center strip.  It really comes down to the details in their docs.   Oddly enough, I followed their recommendations (which is against my nature  ;D ) and everything works fine.

[etd66ss]

There are several good documents out there (google) about installation, not all from the same manufacturer, although it's the same product no matter who made it.  I found it very useful to read their docs.  The recommended fastening pattern is much different than what I would have expected.  Plus these docs have a lot of technical info that's good to know before hand.  I'm going to try and attach one or all of them, but some are pretty big files and I think there's a size limit of attachments.

One very important thing is the recommended spacing for the blocking or horizontal support members.  They recommend 24" max, although mine is closer to 30" and no issues (with the steeper angle, it's less of a problem.  It's also important to allow room for thermal expansion in the panels.  It doesn't take a lot, but it will keep them from buckling.  This is accomplished by using their fasteners, which self-drill the correct clearance at the fastener location.  Also not trapping the edges and leaving a slight gap between the panel edge and the h-strip center strip.  It really comes down to the details in their docs.   Oddly enough, I followed their recommendations (which is against my nature  ;D ) and everything works fine.

I've read all of those, but can't seem to find any technical drawings showing the actual size. To use the H-Profile extrusion, they must be something like ~47.25" wide and not actual 48".

Unfortunately the closest Menards to me is two states over, they seem to have the best selection. Lowes & "Chinesium" Depot have a scattershot selection and nothing 12ft long from what I can see. I'll be ordering my glazing online I guess.

Also, did you use the bubble washers or just rely on the gasket on the screws? I have yet to see any documentation that states the bubble washers must be used.

[btulloh]

One more thing to keep in mind - figure out where your fan board will be located and install blocking at that location.  It's important to block the space above so the air flow doesn't short circuit.  The only path for air flow between the hot side and the cold side should be through the lumber stack.  There'll be plenty of leaks around the ends of stacks because it's hard to seal them perfectly, but the better the seal, the more efficient the air flow through the stack.  Leaks all the air to go around the stack instead of through it.

It's easy to miss this detail, and some of us (me for instance) had to block the gap above the fan board after we were essentially finished, and this was more fiddly than doing it initially.  

[btulloh]

I believe the dimensional detail you're looking for is one of the docs I attached.  I do believe the width is exactly 48".  It's not essential that the edges meet exactly in the middle of the rafter.  fasteners are not used there, except on the outside edges.

[etd66ss]

I believe the dimensional detail you're looking for is one of the docs I attached.  I do believe the width is exactly 48".  It's not essential that the edges meet exactly in the middle of the rafter.  fasteners are not used there, except on the outside edges.

https://www.interstateplastics.com/Polycarbonate-Clear-Extruded-Divide-H-Channel-202-Profile-POLCEXD00315x14400.php

I guess what I am getting at is the H-Profile has a center extrusion, of unknown width because that detail drawing doesn't show the dimension. One or two rafters over and you no longer have a rafter to screw into if the panels are 48" actual...
I'm going to go to my local Lowes & Home Depot and see if I can measure what they have.  

I'll have to order all the glazing before I start framing.

[btulloh]

Having the glazing on hand will increase the comfort level for sure. 

I have no fasteners installed at junction of the sheets and h strip per the recommended pattern, so the rafters don't have to fall exactly at the seems (although mine do). I did a lot of over-analysis before hand that proved to be unnecessary, but unavoidable in my case. My nature. I think scsmith said something about that, like don't sweat the details. For me that's easier said than done, but next time  I build one I'll be a bit more relaxed. Your plan to get the glazing first should improve your comfort level. I think your kiln is going to turn out fine.  

[etd66ss]

Having the glazing on hand will increase the comfort level for sure.

I have no fasteners installed at junction of the sheets and h strip per the recommended pattern, so the rafters don't have to fall exactly at the seems (although mine do). I did a lot of over-analysis before hand that proved to be unnecessary, but unavoidable in my case. My nature. I think scsmith said something about that, like don't sweat the details. For me that's easier said than done, but next time  I build one I'll be a bit more relaxed. Your plan to get the glazing first should improve your comfort level. I think your kiln is going to turn out fine.  

I design everything in CAD before I cut anything, so always sweat the details. It's what I do for a living, hard to break the habit. I never start building and figure it out as I go, not in my nature.
These days, when designing mechanical systems, you can pretty much download 3D models of all the aftermarket parts used in a design (models can't always be trusted though). However, in the construction industry that's not always the case. Materials like this glazing are a crapshoot on whether or not you can actually find even 2D technical information needed to precisely model them in 3D. In some aspects, Architecture/Design seems a bit more "free" than Mechanical Engineering.

[btulloh]

Sounds like you and I have a similar nature. CAD design pays off and makes the actual building process a lot smoother and the results more predictable. 

Selecting fans became a big process for me, converting cfm air flow to fpm based on area and such. I had to analyze the effect of static pressure on cfm ratings to make me happy with my fan choices. Others just bought cheap box fans and installed them and seemed to do ok.  I found the current crop of cheap box fans to have blade designs that caused the cfm rating to drop to almost nothing when subjected to the static pressure in the kiln application. Maybe over analysis but my measured air flow throw the stacks can achieve the recommended fpm for the various species. I guess I don't like to just wing it, but ...  we all have our comfort zone. 

[etd66ss]

Sounds like you and I have a similar nature. CAD design pays off and makes the actual building process a lot smoother and the results more predictable.

Selecting fans became a big process for me, converting cfm air flow to fpm based on area and such. I had to analyze the effect of static pressure on cfm ratings to make me happy with my fan choices. Others just bought cheap box fans and installed them and seemed to do ok.  I found the current crop of cheap box fans to have blade designs that caused the cfm rating to drop to almost nothing when subjected to the static pressure in the kiln application. Maybe over analysis but my measured air flow throw the stacks can achieve the recommended fpm for the various species. I guess I don't like to just wing it, but ...  we all have our comfort zone.

That was going to be the next thing I looked at, the CFM requirements.

[btulloh]

Any progress on the kiln plan?

[etd66ss]

Any progress on the kiln plan?

Yes, but I am spending more time outside these days than sitting in front of the PC designing. I have logged about 30 dead standing and fallen Norway Spruce. Bartering with my brother who has a circular mill, trading wood for his deck for his time to mill up what I need for the kiln.
Just finished the logging today actually, so hope to get everything sawn by the end of the month. Once I know what lumber I have I can tweak my design to suit.

[etd66ss]

I started milling up the creosote poles for the kiln deck & subfloor.



 


 

Logged the last of the spruce I need to mill the lumber for the rest of the Kiln.



 

Hope to start building soon.  Leaning towards a 24ft long kiln so I can dry the 22ft long decorative Scotts Pine beams for my house.

[etd66ss]

Finished the deck framing today. Took longer than I thought to get it all level & square.



 


 


 


 


 


 


 


 

And yes, I know the ground slope will make it difficult to load/unload with forks, but this is just a temporary location near my electrical service for drying lumber/beams for my house. I'll load/unload by hand for now.

[etd66ss]

Some more progress pictures. Progress is slow as I have to wait for the lumber I need to come off the mill, and that only happens when my brother has time to mill stuff...



 

 

 

 

 

 

[Klie]

We are currently building a solar Kiln based off the Virginia Tech First Gen with a few twists of our own for moisture monitoring and fan control. Also doubled up the floor joists. 2x8 construction for the floor. We plan on building a bigger one next but using this as a test. 

 

 

 

 

 

      

[doc henderson]

what was the overall dimension and why did you double up the floor joists?  looks great.

[Nebraska]

Agree with Doc. That looks good ... makes me want  one for my own.