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gbwillson

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Reply with quote  #1 
Hi gang-

Below is a method I devised to stretch screen much tighter than normal. The ZeroPass design requires a smooth, even screen layer to define the air flow boundary, so I needed something better. Screen stapled to a frame will likely loosen over time or even sag if poorly secured. 


Step 1-Nail or screw a 1x2 cleat parallel with the edge of a large workbench about 8” from the edge. This board should be as wide as your frame.

 

Step 2-Staple screen straight and evenly across the narrow end of your screen frame. Make sure to use lots of staples. You may want to wrap this edge around the frame as there is a LOT of stress placed on the screen when pulled.

 

Step 3-Allow enough extra screen wrap the far end of your piece of screen around a scrap of wood(A 1x2works well) 2-3 times. Make sure you wrap the screen underneath the scrap as illustrated, so you have the side of the board to pull on. The wood scrap should be the width of your screen or slightly wider. While pulling this wrapped 1x2 away from the mounted cleat, use one-handed clamps to secure the wrapped board to the table. Continue to pulling and tightening the clamps while pulling on the screen . You will be able to remove any kinks or creases in the screen. You may need to work from side to side by pulling and clamping. One handed clamps are almost required for this step, or a helper.

 

Step 4-This is where we make the screen ULTRA TIGHT! Now that the screen is tight, with no sagging, wrinkles or creases loosely take another board and set it on the screen just behind the cleat opposite the screen frame. This board should be wide enough so you can clamp it from the sides of your work table. Keeping this board upright and tight against the cleat, begin to clamp this board to the workbench. You may have to work from side to side. Continue until the board is tightly clamped to the workbench. Tightening this board while keeping it close to the cleat will pull the diagonal screen flat, thereby pulling the screen much tighter than without. The screen is now ready for staples-LOTS of staples. I suggest using a 5/16" divergent point staple as they hold better. Although I used cheap pine for my frame, I still had to tap down a few staples that were a little too proud. No biggy...

 

Notes:

As you tighten the screen you may have to secure the far end of the screen frame as it may want  to lift off the table. Your frame will likely need a support piece between the two long side to keep them from bowing the side of the frame and loosening the screen. You can pull on your screen quite hard without damage. You should also be able to use this method to attach screen to both sides of a frame. Simply tighten and secure screen to one side of the frame, flip frame over and repeat. Since my collector was built in two 8' sections, I didn't have to stretch screen over 8'. If I did have a one piece 16' collector, I would still make my frames 8' or less.

 

Greg


How to Stretch Screen .jpg 
Clamp board in place
IMG_0632.JPG 


Far end being held down to keep it from rising
IMG_0631.JPG 


Ready for final staples
IMG_0634.JPG 


Final results-NO sagging! I can now bounce a quarter off of my screens
IMG_0650 copy.JPG 



Bert

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Reply with quote  #2 
Neat idea Greg.

I've been going over all the threads about zero pass that span months and years. It's a bit confusing. I drew up a picture that I think is close to what you are doing. Not sure.
I did add 2" insulation because that's what I was planning. Also made spacing 7/8 instead of 3/4 because that way a 5.5" studs would work and I may be using 8" ducts.
Not sure if you are using a total of two or three screens.
Is this close at all?

zero pass 1 closeup.jpg 


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solardan1959

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Reply with quote  #3 
Bert,
  Currently Greg has only two screens and the air flows between them.  We have talked about using three screens and flowing the air between the two outer screens and the center screen so the air has more screen to contact and hopefully more screen will collector more of the heat.
 
Dan
Garage_Hermit

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Reply with quote  #4 
Thanks for the above overview, fellers !

G_H

P.S. maybe the middle screen could, therefore, be replaced by... Cinefoil ?

or FINNED Cinefoil ...
(finned as in, "fan-folded, as in a multiple W shape")

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gbwillson

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Reply with quote  #5 
I currently have a 1" gap for my 4x16 ZP and it is working beyond my expectations...actually well beyond. My performance has more than tripled this year even though I only doubled the size of my collector. Now that the weather is nicer where I can work outside without gloves on I will be opening up the collector and trying a few variations with the screen gap. One recent test was using pieces of yarn inside the collector to study the flow of air currents. At 400CFM the results were quite interesting. Between the screens, the yarn showed a gentle breeze compared to swirling tornado-like flow in the two manifolds. Additionally, the air indicators between the glazing and the screen channel were completely still, I mean, I got down close and could not see even a slight flutter. At higher velocities I'm using, the screen really seems to be doing the job of isolating the air flow from the cold, while still transferring heat to the passing air. 

Last winter with my experimental 4x8 ZP, the air flow choked quite a bit when I dropped a ¾" gap down to ⅝". And at a certain point, I would think the screens would be too far apart for effective heating, but more importantly, it may allow air to flow outside the two layers of screen. We shall see... 

If you were in a double-pass configuration I could see the use of Cinefoil as the middle layer. Maybe the Cinefoil could have a layer of screen laying directly on top. If this was a single pass ZP configuration using Cinefoil, the back layer of screen would never see the sun to be heated. An intermediate layer of screen I think would be effective if the space between the two outer-most screens were too far apart for effective heating. But how do you mount an intermediate layer of screen WITHOUT A FRAME??? I played around with a method were I was able to stretch and install a frameless 2' wide section of screen by hand so tight that that I shredded the screen. Problem is, it's only 2' wide. I'd need a lot more hands for anything wider.

Bert-

Since I used 3½" stud track for my frame I didn't have enough space for insulation thicker than 1". With the velocities I'm shooting air through the collector(350+ CFM) it's likely enough. The air is in the collector and ducts for less than second. Having said that, I may opt for a thicker collector with 2" of insulation for added strength and stability so I can get away without a plywood back. Also, I "think" 6" ducts are fine with up to 96SF collectors IF, and this is a big IF, your ducts have a low EV. So as long as you strive to keep duct runs short and as straight as possible, you should be fine. Since I already have LOTS of 6" ducts, I'll stay with the 6". But if I was just starting out, I'd use 8". How big were you thinking you wanted you next collector to be? And how much air were you planning to put through this unit?

Greg
Bert

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Reply with quote  #6 
Greg

Thanks for the info.

Not sure of the size yet. Been thinking about a 4 x 8 to start with. I will be moving soon and we don't know exactly where yet, so I have to see  how much room I will have at the new place.

I want to move enough air to be efficient as possible without being too noisy.  Was planning on using 12 v fans with solar power. May even use Tom's 3 fan idea, but not sure if that would work in a zero pass.

Planning on building a zero pass, a cinefoil tube and a double screen to compare them. All I can do right now is plan. [smile]





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Bert K.
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mocars2

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Reply with quote  #7 
Would this work/improve things - adding a 2nd ZP with a manifold for both at each end? zp  2 screen adj.jpg
gbwillson

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Reply with quote  #8 
Mocars-

I kinda wondered about having 3 layers of screen, but only having air flowing between two of the layers. A manifold doesn't have to be much larger than the intake if the air is pushed through the collector. But the air volume will have to be large enough to create an overpressure in the intake manifold with a slot for the air to exit through the slot(s) created by the screen layers. I do have a thought about the ⅞" air flow slots. While large, they may have a tougher time keeping the air between the screen layers at lower air speeds. At high speeds the air is kept nicely between the screen layers as I didn't notice any air movement outside the screen layers. But having said that, I didn't check at lower speeds, so I could be wrong. But my thoughts are that the air will take the path of least resistance and stay between the layers for the most part. 

Greg
Bert

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Reply with quote  #9 
I wonder if the airflow between the screens create a static charge on the screens  that may keep the air in between them. 
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Bert K.
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gbwillson

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Reply with quote  #10 
Bert-

That is an interesting thought... If it did, what would determine if the screens were positively or negatively charged. I wonder if you could somehow test for that effect? Drop some feathers into the intake and see if they stick to the screens? What if the screens and the air both have the same charge? Would they repel each other?

Greg in MN
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