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gbwillson

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I'd like to introduce my latest brain fart...ZPDP.jpg 

The drawing is roughly to scale vertically, but not horizontally. I'm hoping to keep the collector around 6" thick. It is a melding of my ZeroPass design and a backpass type collector. After the great results from my ZP collector last winter I wanted to try something different. Space is very limited at my house and the fact that I have to set up and store my collectors each season made me look into a smaller, lighter design based on my ZP work. 

I will be building the ZPDP with as little external wood or steel as possible. Internally I plan to use minimal supports or framing. The top-most screen will not be set in a frame at all but pulled tight from the ends only this saves valuable space and weight. The lower screen will lay directly on the absorber plate made of very thin aluminum flashing. The fins below will not only support the absorber plate but help transfer heat from the plate to the lower section. The angled entry is a flap, or damper that will open and close and also form an intake manifold of sorts. This was a key factor in the success of my ZP design. When high volumes of air are PUSHED into the intake manifold, the air has no place to go but through the manifold slot between the screen layers. This makes the airflow very even from side to side. Tests video confirmed that air within the manifolds is highly turbulent, as is the air between the screen layers. Outside the screen layers the air has little, if any movement.

Not everything has been worked out. I'm still not sure about how I'm going to secure the glazing. Nor am I sure how wide the return needs to be at the air velocities I plan to push through this bad boy, as this will be determined by the output temps. My ZP last year needed high velocities(350+ CFM) or it would overheat.  Actually, I'm not sure about much, other than the journey ahead. I have most of the parts so I will be begin my trek this week. 

Greg in MN[wave]

Bert

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Interesting. Will be great if this works as well as you want.
I can't quite envision what those gray rectangles and circles are. Are those the fins and support?

This is the first design I seen where the warm air comes in from behind. Would be interested on your thoughts about that.



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Bert K.
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gbwillson

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Bert-

The gray rectangles are both the fins and supports for the plate. The holes punched near the bottom of the fins will allow heat to better transfer from the top of the fin attached to the plate to the bottom. I suppose it could add a small bit of turbulence too. The lower section has roughly 2x the space of the upper channel between the screen layers so hopefully the air will slow a bit on the back section and pick up some additional heat before exiting.

As to whether the air enters or exits in front or back of the plate has been studied quite a bit. The cooler, incoming air has far less of a temperature differential so there would be less heat lost through the glazing. The air behind the plate is the warmest as it is tucked between the heated plate and the insulation. But being as a ZP tends to keep the flow of air between the screens and away form the glazing, it may not be as pertinent.

Greg 



gbwillson

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GH-

I always liked the idea of the screen directly on the plate too. I've thought about adding screen to the back side of the plate and covering the insulation as well to help break up the laminar flow and scrub the maximum amount of heat. I have over half of a 100' roll of screen to play with, so why not. I was originally going to use some mini galvanized sheets with a ½" offset as my plate. The screen could have rested on the top of the ridges. But being galvanized, it added too much weight. The very thin 24" wide aluminum flashing I'm using should work quite well and is half the price of galvanized. I like the U-shaped gutter idea, but they don't sell anything approaching round gutters except those made of copper$$$$$. I won't attach the screen to the curve, although that would be ideal. The lightness of the curve wouldn't be able to handle the tension I will be applying to the screen. This will be a horizontal setup as a vertical configuration out in the open tends to act like a sail.[biggrin] I'm thinking about a piece of scrap aluminum flashing, or perhaps clear acrylic for the return curve. Anything I can do to keep the airflow high, the price and weight low will be given strong consideration. 

Greg
stmbtwle

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I'm a fan of the dual pass, but I think the ZP screens should make your hybrid more efficient than either unit alone. Please keep us posted.
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Willie, Tampa Bay
gbwillson

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Will do Willie-

With the ZP having better flow characteristics than a 2 screen collector, I'm hoping it will do better. But as Dan found out, the bottleneck will be at the turn, so hopefully using straight boots and the ZP configuration will offset any flow issues. 

Greg
gbwillson

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I should point out that even though this build is 4x8 and returning back upon itself, I don't expect the performance of my 32SF ZP collector. 16SF is still 16SF of collector surface facing the sun. Having said that, I would expect, or should I say hope for a 30% improvement over single pass ZP. Backpass collectors tend to have rather poor performance numbers compared to other designs. But even if I only achieve the same numbers as my ZP test unit from a couple of years ago, I'll consider it a success since the unit will be light weight and have both ducts at the same end. We shall see...


Greg in MN
KevinH

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Greg,
I think you will find that the biggest benefit comes from having the in/out ducts on the same end (less outside ducting / less heat loss).

You said "Tests video confirmed that air within the manifolds is highly turbulent, as is the air between the screen layers."  What video are you referring to?

My collectors ended up being fairly heavy and the 4x10 size makes them awkward to carry.  I am going to make a small box with two wheels that fits over the bottom end of the collector.  That way I can roll it out of the garage.  If I had thought ahead, I could have put bolts at the bottom of the collector to use as temporary axles for the wheels.

Kevin H
MN
Bert

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Quote:
Originally Posted by KevinH
Greg,
I think you will find that the biggest benefit comes from having the in/out ducts on the same end (less outside ducting / less heat loss).

Kevin H
MN


That is what I was thinking. He can get rid of the longest run if it's set up the same.
Can't wait to see some pictures.

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Bert K.
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gbwillson

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Kevin-

I made a video of my neighbors ZP. We took little pieces of yarn and tacked them above and below the screen channel as well as in between the screen layers. The intake and exhaust manifold areas were quite turbulent, but between the upper screen and the glazing weren't moving. I'll admit it was hard to see much past the top layer of screen, but I would imagine the yarn movement was the same above and below the screen channel. The video sounds terrible as it was a windy day. It was a cloudy day too which didn't help the video. You could see things up close though.  I never posted it due to the poor audio and being 3 minutes long. If I can figure out how to edit the video sound I might post it. 

Last years 16' long ZP had an intake run of about 23' and the exhaust was 8'. So the length of the outside run was about 47' total. At the velocity I was pushing air through my ZP(20.5 CFM), any air was outside for about 1½ seconds. Normally not much time to cool off, but this is Minnesota. 

I like the wheel attached to the bottom corner. I think it was Gary that did that to a couple of test units. I built a dolly to help roll the collectors around, but the wheels would get hung up on any little bump in the yard and made movement a hassle. I hope keep the ZPDP under 30#. But as long as I can manage it easily by myself, I'm happy.

Greg
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