to the Solar CollectorBrainstorming and Development
Water Project 1
Water & Space Heating
I haven't committed to the 4x10 size yet, it's just one idea. Also considering 4x12 (need to rearrange the back room a little bit), 3x12, even a one piece 2x16.I'm juggling several considerations:1) I wasn't planning to repeat the U-turn design for a screen collector. The non-structural (1" polyiso) center divider caused a lot of grief, and it was tricky to get everything in plane at the glazing and to seal everything. I made the divider slightly taller than the frame to ensure that it wouldn't be too low. It ended up slightly high in some areas and flush in others, which worked out OK. It would be better to be able to fasten glazing hardware to the forward edge of the divider, but a structural divider would probably need a structural back sheet as well. Which brings up - 2) Weight. Need to keep it light enough to pick up and move around during most of the construction, since I don't have anywhere to leave it laid out flat. That's why I'm always on the lookout for 'ultralight' methods and materials. I think the aluminum screen frames are the way to go in that regard.3) Performance vs. buildability. I think this is what's pushing me toward a one-way design, at least for a screen absorber. The one way 2x16 was easier to build, except for the joint in the center, which was about as tricky to figure out as the U-turn. The end slots probably reduced performance some. One piece/one way seems to be the answer, although I suspect a 4x10 one way might not be best shape for performance. 4x12 would be better, although I had trouble at times even with the 4x8 carrying it around while still seeing where I was going. That's got me thinking about a 3x12, which, at 36 ft. square, represents a 12.5 % increase in size over both the 4x8 and 2x16. 3 ft. wide would be easier to get a grip on than 4 ft. I can locally purchase a 4x12 sheet of twin-wall, so there would be some waste with a 3x12. Not so much for the polyiso, since the scraps are usable for the frame edges.4) Still looking for ways to build in two sections, but join them into one at some point late in the build. Solar Dan showed the way on track frame design with his experimental 2x16, although I would use stud for the splice member rather than track ripped in half. I also decided it is best to do all your splicing in a straight run rather than at the corners. I think you get the straightest, flattest, track frame by having simple folded corners made from a single piece. Got some ideas to explore. A 2x16 makes good use of available materials. The one thing I don't have a spot for right now is a 4x16 or 3x16 collector.5) Back to the U-turn concept, I really like Kevin's U-turn tube design - you don't even need a center divider except at the in/out plenums, and you aren't applying pressure on the glazing. Another bonus is the paint-free air flow path, which he identified as a priority. Trouble with a tube build is you need a deeper frame, which ties back to the weight issue. Still thinking about it though, either as a one-way or U-turn.6) I'm considering the merits of a polyiso back sheet with no solid facing. Aluminum flashing is pretty light, and I've used it a couple times with good results (3 laps of 14" roll would work well for a 3 ft tall collector), but I'm wondering about gluing some screen to the back side, then painting it. Might be just strong enough, and the screen would reduce damage from accidental bumps.Sorry, I didn't mean to ramble, but I'm looking for a lightweight, economical, easy to build, high-performance design (aren't we all?). I usually end up swiping ideas from you guys and adapting to my circumstances. I still need to test the 4x8 U-turn more before passing final judgement. I should be able to swap ducts between the 4x8 and 2x16 when the time comes. Planning also to build a polyiso square-tube duct, 8" x 8", to replace most of the long input duct on the 2x16. Probably do that first. The square duct will stay in place, and I will just have to fit short sections of flex at each end.Greg - looking forward to seeing your proposed square-tube frame design. Life beyond stud-track, as it were.
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