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dbc

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Reply with quote  #1 
Hello all,

Finally starting my new project, a 2x16 ft. Zero-Pass hot air collector.

It is loosely patterned after Greg Wilson's 4x16:  Landscape layout, 3 5/8 inch stud-track frame, made in two 2x8 sections.  I need to split the collector in half because I don't have anywhere under cover to put a 16 footer during construction.  I will building much of it outside, and I know better than to taunt the thunder-beings during Spring/Summer in Colorado.

Here is where I plan to install- inside the blue-tape markers:

IMG_0687, Wall, 040916.JPG 

The collector will be fastened to the wall, but out about 16 inches on a metal mount.

Here is what I came up with for the cross section inside the track frame, starting from the back:

IMG_0695, Cross Section, 040916.JPG 

Starting from the back:

1) 1 in. polyiso, with an FRP 'skin' glued to the back of the polyiso.  The FRP is a waterproof wall covering used in shower stalls, etc.  It's not really spec'd for outside, but it is pretty well protected under the overhang.  I am also still considering aluminum flashing for the rear cover.  I grudgingly decided to forego a structural back (such as 1/4 in. plywood), because of space constraints (more below).

2)  5/16 inch screen frame, with 2 layers of charcoal fiberglass window screen.  Back frame will have the screen on the top, so space behind the screen to the polyiso is just 5/16 in.  Not sure this is ideal, but space constraints again.

3) 1 1/4 inch screen gap.  I got here by calculating the cross section of the air channel.  Max width will only be 21.5 inches [24 - (2x1.25)], which gives 26.9 sq. in.  I plan to use 6 inch ducts in/out the back; they have a cross-section of 28.3 sq. in.  I know most ZP designs so far use a 1 inch gap, and I can still go there, but I thought that might choke the air flow too much, so I at least planned for a 1 1/4 inch gap.

4) 1 1/4 inch spacer along the long sides to set the screen gap.  Still considering what to use - 1x lumber ripped to 1 1/4 inch, or metal j-trim stacked into a rectangular tube, or stand-offs or spacers with a skin on the outside edge for support.

5) 5/16 inch screen frame installed upside-down, with one layer of screen on the bottom.

6) 1x lumber strips ripped to 3/4 x 1 inch fitted around the edge under the lip of the metal track.  This will just fill the remaining space to hold everything tight, and give support to the glazing.  Glazing will go on top of the fame, with angle hold-downs (drip-edge, stud track ripped in half, or aluminum 1/8 inch angle.

With the above in mind, I cut out the frame pieces, shown here (here you also see my 'workshop')

IMG_0686, Frame, 040916.JPG 

The screens will be 21.5 in. x 84 in., leaving about 9.5 inches on the outer ends for the in/out ducts to enter the collector, with a snap-disc in the output end.  I plan to attach the duct fitting to a sheet-metal plate sandwiched under the lower screen frame and the end-piece polyiso , and glued to the polyiso back with silicone.  I'm not real happy with the lack of support - if the collector flops onto its back, it could rip the fitting loose.  I'll have to be careful until everything is installed.  I will probably disconnect the existing 2-screen collector from the building plenum and connect the new panel instead, at least at first.  Here is my in/out arrangement:

IMG_0688, Ducts, 040916.JPG   

I'm planning to join the two halves together with some metal angle brackets screwed to the track frame, then bolted together.  I wil put EPDM weatherstripping around the square cut-outs on the inner end pieces.  I'm not wild about this either - it seems that building in two sections will restrict air flow a bit through the joint, and raise the risk of leaks - more trade-offs.

My biggest uncertainty is whether the aluminum screen frames are too flimsy to stay square and keep the screen tight.  I just read the discussion in Bert's post in the Construction section; I have been wrestling with all these same issues.  If the screen frames don't cut it, I also like Dan's screen frame (in his 2x16 experimental ZP) made from 1 5/8 inch metal studs.  This will change the internal spacing and require new end pieces with different slots.  I may cut some alternate end pieces, in case the aluminum screen frames don't work.

I like Bert's idea to crimp the frame where the screen is attached.  I am planning to use jute twine in place of the normal spline (Greg's idea), with an occasional crimp backed up by silicone over the jute.  I got some cross-bar clips to fit a brace midway, and some metal corner braces to double the plastic corners.  We'll see.

I read Willie's question about whether you need a space behind the rear screen, and how big.  I have been wondering the same thing.  The rear screen frame on mine will rest right on the polyiso, so the gap behind will be just the thickness of the frame itself.  Any more will mean reducing the inter-screen air gap.

Hope this all works Looking forward to finding out - Don C.

Bert

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Reply with quote  #2 
Don,

Looking good. I think the  1-1/4 spacing is a good idea since the collector is only 2' wide, but I'm sure the experts on here will know better than me.

There's at least three ZPs in the process of being built right now so hopefully we all learn a bit more about them soon.
Good luck with the build.

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Bert K.
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gbwillson

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Reply with quote  #3 

Don-

 Glad to see how you ZP is progressing. A few thoughts...

 As others can attest, using stud track for the frame can be a challenge, due to the limited space and more complicated build issues. I do like it, but I have been looking for other options. Since your collector will be permanently mounted, consider eliminating the slotted sections of stud track between the two ZP halves. Just make a "splice" from another piece of track to hold the two butted halves. And if the stand has a ledger board for the entire collector to rest, it will make connecting the two halves very easy. The only reason I made my ZP with connecting end slot tracks is that my collector needs to be sturdy enough to be moved seasonally for storage. But if you do end up using the slot end tracks, make the track slots larger than the screen gap, say 1¾". I made my slot ends the exact same size as the screen gap and now wish I had made it larger, as I do think it makes for a bottleneck of sorts.

While I think a slightly larger space between the polyiso and the bottom screen would be better, I'd rather see any extra space keeping the upper screen away from the twin wall. Another thought would be to eliminate the wooden lumber frame under the glazing. The aluminum screen frames with reinforcements should be sturdy enough if they were attached to the screen gap spacers. The wooden screen frame only adds bulk and takes up space as well as blocking more of the screen itself from the sun. 

 

Keep taking lots of pics and drawings. They are very helpful!

 

Greg in MNthumb.gif

mranum

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Reply with quote  #4 
If I could have built mine "on site" I think I would have tried to make it one continuous run, but I had to make mine in 3 seperate sections. I was concerned about a disruption in the air flow as it went from one section to the next so I made my slots a little bit larger than my existing screen gap. The thought was also that I could play around with screen gap differences and not worry about a restrictor between the sections.

Looking forward to seeing your results!  [smile]

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dbc

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Reply with quote  #5 
Greg, Mranum,

I am re-evaluating some of my design decisions in light of your suggestions:

1) I would prefer to build a single full-length frame (I always did), just need to figure out if I can do it, and how.  My main reason for having 2 sections was protection from the weather during construction.  The other reason is that the big-box stores here only carry 25 ga. track.  It's kind of willowy.

Maybe I could still build in two 2x8 sections that butt together, but permanently attach the frame splices to one side only (left or right).  Then, permanently join the second side and finish sealing 'in the field', when I attach both halves to the mount.  Use temporary end pieces to keep the 3-sided frames together while I still need to move them around.

Another idea is to build the frame 2x16, fitting in the polyiso back piece before riveting the last 2 corners, then attach that assembly to the mount.  I could do the screens and other detail work 'in place',and cover up with plastic sheet while I am away.  The trickiest part to both above ideas may be the glazing.  I could take the almost-complete panel back off the mount and install the glazing flat.  if I went this way, I would make the bottom and both sides into a 'U', with a splice in the middle (an inverted version of Solar Dan's ZP frame), and make the 16 ft. top as a 'cap' that I could rivet on after dropping all the internal parts in from above.  Either way it's worth some thought (and another 50 ft of track), if I can dispense with the slotted frame pieces midway, with their attendant performance and sealing compromises.

If I stay with the 2-piece design, I will at least open up the slots a bit.

Greg, I was planning to have a support piece under middle 4 feet of each frame section, so there would be 2 ft on each end of the collector and 4 ft. in the middle that wouldn't have direct support (2 + 4 + 4 + 4 + 2).  This spacing could be changed, or I could incorporate a longer, continuous member under the whole collector.

2) The biggest reason I planned to use 1/4 in. plywood strips against the inner wall of the track, along with the 3/4 x 1 in. piece of wood under the top lip, was to provide a screwing base for the glazing hold-down pieces.  I don't expect these wood pieces will improve stiffness much, and I wouldn't mind leaving them out, and just tight-fitting 1 in. polyiso directly into the channel.  That would sure make for a light-weight collector.  Downside is that this leaves only the stud track frame to fasten anything to.

What I am really looking for is a way to fit everything as a 'sandwich', held together by the 1 1/4 in. stud-track flanges.  This would reduce the need for extra bracing just to hold the screen assy in place against the back.  I also would like to avoid screwing through from the outside to hold the screen frames (one of the reasons I considered wood screen spacers).  If I fit 1 in. polyiso in the track channels, that leaves 1/4 in. - maybe that's enough, I don't know.  Another idea is to use 1/2 in. polyiso inside the track.  That would provide more overlap surface for the sandwich, and would move the 3/4 in. wide screen frames almost completely under the track flanges.  As a bonus, the solar aperture would expand by 1 inch (4.9% on a 24-inch wide track-framed collector), basically exposing the whole area not taken by the track itself.  I could use a second strip of 1/2 in. polyiso as the spacer between the screens.  With some silicone and foil tape, and a tight fit, it might hold together.  The obvious trade-off here is less insulation around the sides.

I would still probably need some type of cross-members at each end of the screen assembly to keep the air directed into the screen gap.  Also would need something under the joint between the two glazing pieces - something I could screw a cover-strip into.

3) I am also looking for a good way to attach and seal the twinwall glazing, preferably something I could take off and reattach if necessary without the holes stripping out.  The angle brackets used by many of you would seem to require something for the screws to bite into.  I'm not sure the 25 ga. track is enough.  Palram doesn't recommend drilling through the twinwall for attachment except in the most 'quick and dirty' applications (mine?).  I am trying to visualize some type of adjustable or spring-loaded clamps that would hook around the frame and pull the glazing tight against the front.  I am also considering some long thin bolts, or all-thread, passing through the glazing cap piece, the glazing, and the track frame, all the way to the back, with nuts to pull it together.  I like Krautman's idea of a separate glazing carrier that fits over the front, but that may be a little beyond my capabilities.

I will keep plugging - now if the state-of-the-art would just sit still long enough for me to actually build something...


mranum

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Reply with quote  #6 
The flimsy-ness of the track is why I glued a 3/4" board inside of mine, and also it gave me a good base to screw into. My glazing is sandwiched in place with an angle cap. The angle was track that I ripped in half. Worked really well and cheap. I used pole barn screws for mounting. While not real pretty, they do grip very well. edge.jpg 

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If the women don't find you handsome, they should at least find you handy.- Red Green
dbc

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Reply with quote  #7 
Mranum - Good ideas there.  Your glazing looks real solid.

Does your collector have a polyiso back?  If so, did you put the back in first, or the side-boards?

I originally planned to use 1/4 in plywood + 1 in. polyiso on the sides, although I'm not sure 1/4 plywood will hold screws much better than the bare track - maybe once.


gbwillson

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Reply with quote  #8 
Don-

I used ⅜" plywood on the sides and back and ¾" for the ends. The side plywood was glued with in place with an industrial construction adhesive, to add rigidity as much as secure attachment points. I also glued the back plywood sheet to the track with more construction adhesive. In a few key places I added extra pieces of wood. The biggest issue is almost everything is attached from the inside, such as snap switches and thermometers. But with track, you have to attach in many cases from the outside in. Taking the time to trim and file down the overlapping corners so they fit snugly and make sure you do a dry fit first. Rivets worked pretty well for connecting the corners, but you will want to use larger diameter rivets. They're much stronger, but are more difficult to snap off tightly. I should add that the metal may be thin, but once you tie pieces together, add reinforcements and mount it on a stand, it will be much stronger and less wobbly. 

There are a lot of ways to attach the glazing. But with a track frame, it really has to be outside, on top of the track. I like the look of the track inside, but it left me with too many compromises during the build and no room to work. While I attached the glazing trim to the sides of the collector track, I'd look for something different on my next collector. Your screw holes need to be VERY accurately drilled so  the weatherstripping is uniformly compressed. Krautman has the right idea with the single piece frame/glazing cover. It might be something worth looking into rather than separate frame pieces and separate glazing. It's all one big(but still light) cover. Once the "cover" is on, maybe clips or hold-downs of some sort could secure it in place and still allow quick and easy access, if need. And it WILL be needed at some point.

Greg in MN


mranum

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Reply with quote  #9 
Yes I have 1/2" polyiso in the back and sides. I assembled 3 sides, fitted the polyiso back layer then attached the other end. Then cut the boards for a tight fit inside the track. I used construction adhesive to bond board to the track. The boards are cut so the ends lock in the side pieces. Everything fits very snug. After the boards were fitted I added 1/2" polyiso over the boards with foam adhesive. The boards and poly make a sandwich that is the same thickness as the track.inside.jpg

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If the women don't find you handsome, they should at least find you handy.- Red Green
dbc

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Reply with quote  #10 
Finally getting back to the 2x16 ZP.  Recent circumstances have kept me othewise occupied - 48 hr weekend snowstorms and rainstorms, broken trees, flooded basement, damaged floors, new sump pump, not to mention my day job.

Anyway, I 'hogged out' the slots on the inside end pieces (review - plan is to join 2 ea. 2x8 sections end to end) to 1 3/4 inch.  Like this:

End pieces.JPG 

I fit all the track pieces together loose; so far so good.

I debated whether to fit the back panel or 3/8 inch plywood stud-track reinforcements in first.  Decided to put the plywood in first, since the back will take up the whole area between the rear edge of the slot (outside in above pic) and the track, which would mean the plywood would be just a shallow 'U'.  I cut the plywood pieces and fit them into the track sections.  The 8 ft. pieces go all the way to the end, while the shorter end pieces stop 3/8 inch short.  Here are some photos of the track with wood installed:

Frame with wood.JPG  Close up - frame.JPG 

Then I encountered my first setback - I tried to fit the corners  together, but realized the folded-over track ends need to slip under the plywood.  Tried to shoe-horn it together with a taping knife, but popped the still-tacky Liquid Nails glue loose.  Thought about that for a minute, then pulled all the wood loose and scraped the glue off.

Not sure yet how to fix this.  The last 2 corners will still have to fit under the plywood, since I need to put the back in before I finish the frame.  Maybe go back to original idea of fitting the back first, then the side reinforcements.

Also still thinking of how to make a single 2x16 frame, or better yet - 2x8 sections that can be joined together right at the end into a single 2x16.  Or else get new track and do the corners another way.

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