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gbwillson

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Reply with quote  #171 
There have been a few ZP collectors using turns. The most recent two are here:

http://simplysolar.supporttopics.com/post/jakes-solar-north-of-50-9446061?&trail=10

Both of the units have multiple turns as you can see if you look at Jake's post #3.

Greg in MN

KevinH

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Reply with quote  #172 
HauteGaronne,
My U-turn standard screen collector works fine.  One thing I didn't take into account was that with the U-turn I doubled the number of screens the air has to pass through.  2 layers of angled screen = 4 total layers it has to pass through with the U-turn.  3 layers = 6 total layers to pass through.  I don't know how much that restricted the air flow, but it can't be helping.  The screen went into the end where the air flow turns (a simple divider down the middle that ends before the turn).  I might try some sort of parallel screen method like the ZP if I build another screen collector.  After the old one I built, I went back to using tubes (just a personal preference).

Keep asking questions and when you decide on the collector type, tell the group what you plan to do and they will comment.  All designs will produce heat, but a collector that doesn't get built produces zero heat.  When I built my first collector I spent too much time designing and missed the first heating season.

Greg,
Yes, I remember those.  What I should have said is that I don't remember anyone studying the effect of the turn(s) on the ZP flow.  I'm just guessing that with a plenum and separate exit/entry slots (instead of one in the divider) you could get a similar effect as the plenum where the air enters in your collectors.

Kevin H
MN

Ashley

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Reply with quote  #173 
Are their detailed plans for building the zero pass hot air collector?  Where can I obtain them.

1)Anyone know the net loss of heat (relative) if you angle your solar hot air collector to your Lat. verses placing it vertical on building?  I have tons of insulation so super insulating the angle area at the bottom is no extra cost to me.  Since I'm in zone 5 with only 2 days of sun out of 7, I would like to gain as much heat as I can.

2) I was going to build a 3 screen collector until I saw the ZP flow.  Is the ZP much more efficient than the 3 screen, if so how much.

Thank you so much for the research.

SolarInterested

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Reply with quote  #174 
Welcome to our community Ashley. Have a look through the 'Member Projects' section for folks who have built Zero Pass collectors. There's also a side by side trial with a regular screen collector somewhere on the forums but I don't have the link handy. Hopefully someone else here has a better memory.

Mike  

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gbwillson

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Reply with quote  #175 
Hi Ashley-

Welcome! 

1. There are no "plans" per se, much less detailed plans for the ZP as every build is different. However, the build is very similar to the 2 or 3 screen collector where the screen layers are angled and the air passes through the screens before exiting the collector. With a ZP, the screen are parallel the glazing and the air passes BETWEEN the screen layers that are a specific distance apart. The  idea is to make the air enter the screen gap via a manifold. The manifold is nothing more than a boxed off area with a slotted opening along one side that forces the air into the screen gap. Air entering the manifold swirls around but has no place to exit except for the screen gap. This gap helps even out the flow from side to side to eliminate hot and cold spots within the collector. Below is the basic manifold/ screen slot entry. This would be adjusted slightly should the collector box be deeper. The main point is to prevent air from leaving the manifold except into the screen slot.

ZeroPass Intake Detail.jpg 
Here is a basic front view, although duct placement isn't critical. 

ZP Top view.jpg 
2. The ZP can be mounted either vertical or angled. Vertical can take advantage of the sun reflecting off the snow or add-on reflectors. Vertical mounts to the side of a building also keeps exposed ducts to a minimum, and eliminates potential snow buildup on the face of the glazing.

3. The ZP does collect more heat than a 2 or 3 screen collector. The reason is that the angled screen collector gains most of its heat when air passes through the screen layers. And before and after it performs similar to an empty black box. Yes, you could add many layers of screen, but that adds resistance and restrict airflow, which makes it difficult to move collected heat out of the collector box. The ZP, on the other hand heats the air continuously from beginning to end as it travels through the collector as the air moves between the two heated screen layers. This also keeps the moving air away from the cold glazing. As the air passes between the screens, as opposed to through them, the ZP has very little air restriction. And this is very important because...

The ZP needs a LOT of airflow keep it from overheating. It's a nice problem to have. High airflow through a collector is more efficient as it moves the warmed air into the house before being lost or wasted. A standard angled screen collector begins to falter as airflow increases. This is because the air is trying to pass through the same area  of screen, and the sun can't keep up with the heat being extracted. As mentioned earlier, the ZP does require a larger fan capacity, and the screens should be a specific distance apart(1⅜") so you need to make sure the screens aren't loose or sagging. 

So how much better is the ZP over an angled screen collector? I would say double, if not a bit more... 


Greg in Minneapolis




stmbtwle

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Reply with quote  #176 
I can see what might be a problem in the above diagram. The incoming air is going to impinge on the twinwall, probably losing heat in the process. This is exactly what the ZP concept is supposed to prevent. In all of my collectors I put a piece of black flashing a bit below the glazing, following the examples in Scott's screen collectors. The black flashing deflects the air, at the same time acting as a "backpass" and transferring heat to the air.
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Willie, Tampa Bay
gbwillson

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Reply with quote  #177 
Willie-

Agreed. Since I made this drawing, I have thought about modifying the intake, either by a deflector(clear or otherwise, adding screen inside the manifolds, and having the front of the manifold insulated instead of clear glazing. But on my current setup, My intake ducting has about 25' of exposed ducting which can cool the intake temps several degrees as air moves from the house to the collector intake. And the cooler air will be less affected as it hits the underside of the glazing. In any case, it still works great and pumps out large amounts of BTU's. But any design can be improved, and with the addition of the increased screen gap, the ZP will only get better.

Next ZP revision will address this, and should add a small bump to the performance numbers.
JC77

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Reply with quote  #178 
This is probably the dumbest question in the history of solar but has anyone ever tried painting the inside of the collector white? If the screens are black and everything else is white, wouldn't there be less energy absorbed in the box and more reflected/absorbed in the screens? The collector glazing is only going to let so much light in regardless of what color the collector internals are.

The way I'm understanding a zero pass, the air between the top screen and the glazing is mildly stagnated along with the air between the rear screen and the back of the collector. The two layers of screen basically act as hot walls the air passes between/around? It obviously has to interact with the screen to pick up heat. Anyway, I read a lot of discussion on low mass collectors being better at getting heat out of the absorber material and wondered of doubling up the screen on each layer and painting everything else white would have a reflective effect to put more energy in the absorbing material (screens) and less into the collector.
stmbtwle

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Reply with quote  #179 
That has been discussed ad nauseum but as far as I know, no-one has done an actual side-by-side test. Are you volunteering?

Yes, the glazing will only admit so much light. However, if anything in a collector is NOT BLACK, you can SEE it, which indicates to me that some of the light striking it is being reflected back out, and lost.


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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
JC77

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Reply with quote  #180 
I'm currently researching solar air heating. It would be pretty easy to change collector color if you wanted. Just wondered if it had ever been tried. It's easier to learn from someone else's mistakes! That's why I mentioned doubling up the screen layers so there'd be more "black" in there to absorb light and it wouldn't look so white thru the glazing. I'm only building one collector so I couldn't do side by side tests. I guess I could test an empty white box before I put the screens in. Kind of a moot point though. A white box with no absorbing material shouldn't produce much heat. But I could run a white zero pass for a while and gather data, then paint it black later on and see what happens. Just throwing it out there to see if it had been tried and maybe save myself some trouble.
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