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dbc

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Posts: 303
Reply with quote  #1 
In my thread for the 4x11 collector, some of us were discussing the depth limitations of 3 5/8 inch metal stud track as a frame material.  One proposed remedy was to move the polyiso back sheet outside the track, and hold it in place and protect the raw edge with pieces of ripped track.

I made the following sketch to illustrate the idea.  This is an 'edge-view' near one end, looking into one of the plenums from the top or bottom:

3) Concept - Deep track frame, 100119IMG_1143.jpg 

I figured that two 1x2 screen frames + 1 3/8 screen gap adds up to 2 7/8 inches.  This leaves 3/4 inch to fill.  I have shown the rear screen frame right against the back, with the front screen frame + a second 3/4 inch (1x2) spacer in front to block the open space right under the glazing.  The second 1x2 brings the stack right out to 3 5/8 inches, same as the track frame.

This is probably the simplest assembly, using common materials.  The spacers could be split (3/8 in front and back), or you could add a second 1/2 inch polyiso sheet to the 1 inch piece shown, leaving you with a 1/4 inch space to fill right behind the glazing.  Lots of ways to tweak this.

The 'outboard' polyiso sheet could be glued to the back flange of the track frame, then further protected with ripped pieces of track screwed into the side of the frame.  This same idea is shown for the glazing.  I have used this method on the glazing 3 times now, and it seems to work OK, at least with my fan.  A super-powerful fan might overpower the glazing angles, I don't know.

johnfmonroe

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Reply with quote  #2 

dbc, I have been following your concepts & I have really been influenced by you. There is much I don't understand. Why do you need spacers? Is the spacer on the bottom just to get the screen up enough to allow air to flow under it. And is the 1 3/8 " between the screens the optomin distance to allow for the best heating drawn from the screens.  And why is a spacer needed at the top? Thanks. I'm trying to get the concept about this. I just sent for some screening to try this concept & see if it is stable enough.   The idea is to mass-produce 12" x 4' screens bent around the 2x12  & put them end to end & side to side in the collector. I look at aluminum screening like paper, paper can be very strong with the right bends. At my age & getting up on my roof, I am trying to build as light as possible, and so to build without frames for the screening, if I go this way.


John in IN so simple.jpg

gbwillson

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Reply with quote  #3 
John-

I like your idea for bending aluminum screen material to form a rigid shape. To make crisp, sharp corners you may want to rip down your boards to remove the rounded corners, as sharp bends will make the forms much more rigid. Another thought is to make a mold or form to "mate" with the ripped down board. Simply place a section of screen between the two mating pieces, and push them together to form the desired shape. 

You may want to adjust the width of each screen piece so it exactly fills the width of the collector. For example, a 4x16 ZP might need about 44" of screen to fill. This means 4-11" wide formed screens.

You have a lot of great ideas John! You should start your own topic to keep any ideas and discussion about your build(s) in one place. 

Greg in MN


stmbtwle

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Reply with quote  #4 
My experience with aluminum screen is it's stiff and springy and very hard to get to lay flat. I think forming it around a flat board would be a nightmare.
Since it already comes in a roll, suppose you were to make round tubes instead?

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
johnfmonroe

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Reply with quote  #5 
I was at Menards today, what a store. I haven't been there for a few years. I like it better than Lowes. I found one piece of cut wood for my mold. 1 1/2" x 11 1/8" x 4'. It has a bad split so it is being glued right now. My screening should arrive from Amazon tomorrow or the next day & I will see how the molding goes. As stumbtwle says if the finished product is too springy to lay flat mayabe a simple thin wire 1 1/2" long with a bent hook at each end would slip through the screen & hook it at each end to keep the spacing. Perhaps a better way would to rip a saw cut down both middles of the board on both sides. As the screen is applied around the board, take a wooden slat & drive the screen into the to create a stiff center on both the top & the bottom. As soon as I shape a screen we can evaluate it to see if it is a waste of time. I'm not sure how to start my own topic but if I have enough to contribute later on I will try that. But mostly what I am doing is coming from you guys. Here is my moldboard. I am so happy I found it so easily. It was the only one in the whole place. I checked out the 4x8 polycarbonate multi-wall clear glazing $42.99. It looks nice & would be easy to put on the collector. 
John in IN
IMG_0094.jpg
johnfmonroe

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Posts: 43
Reply with quote  #6 
ROUND TUBES. Just thinking out loud. Bear cans are round tubes. I have never seen any of them measured for heat but here are the problems with round tubs as I see them through my foggy mind. The sun will only strike a beer can on one tiny area. Then as the can roles away from the sun & finally into shadows you get less & less sun. The only way I see a round collector being efficient is when you have it setting in a  parabolic troff that concentrates the sun on it.
stmbtwle

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Reply with quote  #7 
I'm not talking about beer cans, cinefoil, or even downspouts.  I'm talking about SCREEN.  The end result would be little different from your "formed" screen box, though IMO it would be a lot easier to make.  Just a thought, it's your collector.
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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
johnfmonroe

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Reply with quote  #8 
Screens are different & I don't understand them. Because sunlight passes through screens it makes a difference I think. So honestly I don't know how to think about them. To understand beer cans & pop cans, take one before your computer screen that is lighted up, turn off your lights & with the room black, you will see about a half-inch of a light strip on the can & the rest of the can will be dark. This represents sunlight striking the round cylinders. I admit I don't know how a screen works like this. If I had some unpainted aluminum screen one could take a round roll the size of a been can & see what it looked like in the computer room & compare it with the beer can experiment. 

John in IN
johnfmonroe

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Reply with quote  #9 
So thinking about this a little more. One could take a piece of flat unpainted screen the with width & length of a beer can, and a round roll, just one layer of screen, of unpainted screen the size of a beer can, turn off the lights in front of the bright computer screen & see which is lighted up the brightest. This would tell you a lot, I think. I think the tube screen would be in the shadow but I don't know that without the experiment.

John in IN
stmbtwle

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Reply with quote  #10 
I wasn't thinking of ONE tube, but a whole lot of little ones, say 1-1/2, 2 inches in diameter, laid side-by-side like you would a pop can or drainpipe collector, with the air being blown through the bank of tubes, as I understand you're planning to do with your formed screen. It would probably have more back pressure than yours but I think otherwise it would be very similar.

All things considered, I think your design is better, I'm just afraid it is going to be a PIA to build. You'll know soon enough.

I tried to make an aluminum screen collector a few years ago. After an hour or so of trying to get the screen to lay flat, I gave up and switched to fabric screen, which is easier to work with, and you don't have to paint it.

Something we discovered a while back with pop can aluminum. If you heat it with a propane torch (it doesn't take much) you take the spring out and it's much easier to work with. I don't know if it would work with screen.



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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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