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gbwillson

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Reply with quote  #21 
Don-

I like what you experimenting with the new ZP build. Like you, I don't want another two part collector. That's why I had to curtail my latest ZP. As a single 4x16 foot unit, it didn't fit up the basement stairs from the workshop. Had the fall weather stayed mild a couple of weeks longer, I might have been able to finish it up in the garage. But it was not to be. And like your ZP I had to make the back screen frame a bit thinner as the ¾" frame partially blocked the narrow 1" gap in the connecting wall gap. The stud track framing simply didn't have the depth, especially since I also had a ½" plywood back. Hence, I couldn't widen the connecting gap. I won't be using stud track in the future. In many locations where the stud track was reinforced with wood, including the entire perimeter of the collector, rust formed where the metal and wood met. Not good...

I had screens at both ends of my ZP and I see no problem with them being in the plenums as long as no screens impede the path of air. After all, the air in both of the plenums swirls like crazy, so why not add the extra screen area to better transfer heat to the air. 

I do think you could get away with pulling the air through the collector instead of pulling. The narrow 2' wide channels won't have the problem the 4' wide units do, where the air that is drawn through the channel doesn't spread out the full width. I did play with a simple deflector, attached to the intake manifold, that deflects the draw air to the sides instead of straight down the middle of the screen gap. In any case, your turn is likely going to need a little bit of help if you pull the air so the air doesn't bunch up on the inside corner of the turn. 

It might be worth experimenting with the airflow pushing versus pulling before you do a final sealing of the unit. I don't think it will take too much more CFM input than the 2x16 unit. It will be very interesting to see how the two unit compare, both flow and output temp-wise. 

Greg in MN

dbc

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Reply with quote  #22 
Greg,  When I built the 2x16 I reconfigured the ductwork so the fan pushed air into the intake (it was the other way originally on the slanted 2-screen).  I'll probably leave it pushing, at least at first.

I think I may be at the end of the road with stud-track frames too.  They really looked like a good answer, and they are for about 90% of what you need to do . It's that last 10% (fixed, limited depth mostly) that trips you up somewhere.

Since I'm committed already on the new 4x8 build, I'm looking for ways to make at least one of the screen frames thinner.  I had limited success with the generic aluminum screen frames; they were really light and low-profile, but I couldn't get the screen as tight as I wanted, and I wasn't sure I could double the rear screen (I ended up leaving it single).  Also, the framing seem to be a seasonal item, at least around here.

I came up with a couple ideas: (1) Make the rear screen frame out of a piece of 1/2 plywood, with most of it cut out.  Little worried about out-gassing where it's cut, although there may be 'greener' varieties.  I could paint it completely with primer before the black coat; that might seal it enough.  Also, I don't know if it would be stiff enough.  (2) Bring the front screen frame out a little bit past the track frame.  The felt weatherstripping I purchased to re-do the gasket between the 2 sections on the 2x16 is quite firm.  I doubt I can squeeze the 1/4 inch felt much more than 1/16 inch with my bare hands.  It worked pretty well where I used it; it made a good seal.  I covered it with foil tape, since it was outside the collector proper, but that may not be necessary for a glazing gasket.  If I glued strips around the front edge of the frame, where the glazing rests, the screen frame could stick out maybe 3/16 inch past the track and still be flush with the felt gasket when it was slightly compressed.  I figure I need 1/4 inch more frame depth to have a 1 3/8 inch screen gap with 1x2 screen frames (I don't have a plywood back), so I could get the gap out to 1 5/16 - close.

Looking down the road, I'm considering frameless, basically a polyiso box with aluminum flashing skin.  I could still have plywood strips around the sides, between the polyiso and the flashing, as anchor points for screens and/or angle glazing hold-downs.  The plywood could even go inside the polyiso.

It might even work for a 2x16 (or 4x16) - with a little extra time and money, you could make a 2-layer polyiso back, two 2x8 sheets end to end, backed by 3 sheets of different lengths, say 5+6+5.  Have to draw a picture.  Seems you need to do something to avoid a 'hinge in the middle' if everything is built from 8 ft. long material.

Sorry to hear you had rust problems with the track frame and plywood.  have to keep an eye on mine.  How did your design work out with the square tubing and snap-together corners?  Or is that the one that got put on hold for winter?
gbwillson

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Reply with quote  #23 
Don-

Yup-The square tubing frame ZP was put on hold. As I putting up last years ZP I noticed it needed some help. Not only was the unit rusting alone the edges, but I needed to open the unit up in order to add a braces to keep the glazing panel hold downs from ripping out from the air pressure. Last year I had to make do with external braces. Unfortunately, as soon as I opened the unit up in the garage, the weather turned cold enough to prevent some of the needed repairs. But the time I finished repairs, the weather has turned cold enough that I could no longer finish building the new ZP unit outside, and it would be too large to fit up the stairs from my workshop. 

I think you may want to reconsider using screen frames, just not the ones you find in the big box stores. They are thin metal and narrow. Here is a site that does nothing but screens. They carry thick and wide frame pieces, in lengths up to 8' long, so there is little waste, which makes the prices as good or better than the cheap frames sold at the big box stores. They carry metal and plastic corners, both inside and outside mount. You can also buy frames either 5/16" or 7/16" thick, either of which is far thinner than you could build a wood frame. And a thicker, wider frame should be plenty strong enough to allow for tight screens. You might also consider making screen frames smaller. So instead of 7' or 8' long screen frames, make two smaller frames. It takes more corners, but you should be able to make the frames tighter than larger screen frames. Krautman made large frames, but added a mutton as well as sheet metal triangle reinforcements at the corners and muttons. Seemed to work pretty good, but with the thin framing pieces he used, the sure felt like flimsy, but there was no sag.

http://www.qualitywindowscreen.com

And if you are going to try out my Chicken Wire screen holder, you may not need a support all the way around the perimeter. And if you do need full perimeter support, I'd rip board stock before plywood as there would be no glues to worry about.

One big advantage you have with any lightweight build is your collectors are permanently mounted. Moving and storing the collectors certainly takes its toll as the collectors get banged and tweaked each time I have to move them. And being they are out of the prevailing winter winds, the backs don't need bracing like my units that sit exposed to the winter winds.


Greg in MN
dbc

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Reply with quote  #24 
Greg,
You've convinced me to take another look at aluminum screen frames.  Quality Screen certainly has everything you need, even black aluminum screen (no painting required), although it is only available in 100 ft rolls minimum.  The price might send me back to fiberglass, which is a lot cheaper.

I could make only the back screens with 7/16" aluminum framing and still use 1x2 wood for the front; that would give enough depth for a 1 3/8 inch screen gap.  The reason I am thinking of wood for the front screen is that I didn't plan to attach the center divider wall to the back of the collector (not much there anyway - just polyiso and flashing).  I was going to make the screen insert so it could attach at the sides only.  The center divider would join between a center rib on the front and back screens, forming sort of an I-beam running down the center of the screen assembly.  It would still work if I attach the divider to the front screen only, and have the divider pressing down on the back screens.  In this plan, the back screens would be only half-width, so the two adjoining frames would meet in the center.  I am working on a sketch right now.

If I make both front and back screens out of the aluminum frames, I will need some sort of 'skeleton' to hold the center wall in place.  Thinking about that too; it could work.

The biggest problem I had last time getting the screens smooth and tight was the somewhat 'kinky' sisal rope I used in place of the standard vinyl spline.  The frames themselves didn't bend much, since I used a cross-bar every two feet, and added flat corner brackets at all the corners.  Do you know what Krautman used to hold his screens?  If he used vinyl spline, did he have any problems with heat?  Did he reinforce or cover the spline with anything?  (glue, tape, crimps?)  One more question (sorry) - did he use 2 layers of screen on the back screen?  I wonder if you need to drop one size on the spline to do that.
dbc

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Reply with quote  #25 
Getting ready to shift gears on the internal design of the 'turnaround 4x8 ZP:  Most likely plan now is to use separate 7/16 inch aluminum screen frames for the upper, lower, and turnaround areas instead a single wood frame assembly.  This is leading back to 'ultralight' assembly methods (like on the 2x16 ZP), as explained below.

What's different is that I now have to figure out the center divider - whether it will be part of the absorber assembly or permanently attached to the back panel.  Leaning towards the second idea.  Since there is no real structural back, just polyiso and flashing, I thought about making the divider out of 1 inch polyiso and gluing it to the back.  To test the idea, I made some test panels, using (1) Gorilla Glue (polyurethane), (2) Liquid Nails, and (3) Silicone.  I made one test panel with the foil facing removed from the back, and a second with the foil left on.  I also made a single panel with the foil left on and the mating edge of the divider wrapped with foil tape (the tape on top is not part of the joint).  I only tried silicone with this last method.  I put a 2 1/2 inch construction screw into each sample to hold it together while the glue dried.  Here's a photo.  The panel with the foil peeled off is on top:

Glue samples, 012818.jpg 

Next day (yesterday) I checked the samples.  They all felt pretty strong.  I could flex the whole assembly before any of them broke.  I haven't tested to actual failure, but the samples without the foil seemed a bit more solid; on the others I could hear the foil bond just starting to 'crinkle' like it was about to separate from the foam below.  I was surprised the silicone held as tight as it did; I think that would be a usable option.  The Gorilla Glue my be the strongest - it felt like a single piece.  The Liquid Nails was also strong, but it still had a smell, even today (2 days after).  By the way, the Gorilla Glue was old (kind of thick) so it bubbled out quite a bit.  The silicone was easiest to smooth out into a nice bead.  The silicone and Gorilla Glue left no noticeable smell.  In summary, I think I can make a center divider that will be strong enough.

Second problem is what to attach the screens to.  (I was going to screw through the sides of the track frame with the wood screen frame.)  I got some pieces of poplar, 1 3/8 x 1/2 and 1 3/8 x 1/4, real nice stuff, straight, no flaws.  Tentative plan is to make small 2-layer inserts out of 1/2 inch poplar and 1/2 inch polyiso and glue them into the stud track, poplar side out, where the screens will attach, then fill in all the rest with 1 inch polyiso.  The center is a little harder; idea here is to 'inlay' pieces of the 1/4 inch poplar (have to cut out a pocket in the polyiso beforehand) and probably also run a strip of foil tape over the raw top of the divider.

Still working out how to attach the screens, but I'm hoping to attach the back screens to the wood inserts and then drop the front screens onto some protruding screws with a spacer between the 2 layers.  That way I'm not trying to screw into the wood right at the outer end.  All these methods are borrowing heavily from the 2x16 ZP, which was a little knick-knacky to assemble, but such is the consequence of changing plans mid-stream.

Also still looking for a way to make the center divider part of the screen assembly and just attach at the sides of the frame; not as far along on that idea.

While we're stuck with weather too cold to glue or paint, I made the snap disc bracket and drilled all the holes for that bracket and the electrical box that will go behind it on the back wall.  Here's the bracket:

Snap disc bracket 02, 012818.jpg 



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