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dademac

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Reply with quote  #11 
Gordy,
Minnesota

Thanks for the kind words. I do not see criticism only see ideas and advice from those with more experience. I like the idea of putting a sheet of polyiso under the screen loops or I am toying with the idea of trying to push down every other loop. 

Has anyone made a venturi in their existing heater duct? I have a heater duct close to where the heat comes out of the panel. This would suck the air through the panel but I would need a way to shut it off when the sun isn't shining.

dademac, Kansas

gbwillson

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Reply with quote  #12 

Thank you dademac!

I stopped by my friend Krautman’s this morning and showed him photos of your collector. He had the same initial WTF reaction that I did. Because the design was so different at first glance, we kind of poo-pooed the idea initially. But then we started talking about your design. And we talked about it more and more and more before long, we realized that if this was a conventional collector design, we wouldn’t have bothered to talk about it at all, much less brainstormed about it for nearly two hours like we did. 

Yes, the fact that there are 60+ layers of screen for air to pass through was the big issue. As was the fact that much of the air can bypass the screens at the back of the collector. But then we began to look at how this idea has so much going for it and could be improved with a few minor changes. One of the changes we thought might be helpful was that the loops themselves are too tall. As it is now, the upper loops of the screen are touching the glass, which in turn transfers cold to the screens. Also, the tall loops would shade the lower parts. The loops being so tall, may not be able to transfer heat through to the lower portions of the screen. So shortening the loops to roughly half the height might help. Shortening would also keep the majority of the air passing through the collector away from the cold glazing.  

The second thought we mulled over was to turn the loops 90˚, inline with the airflow. This makes air pass between the loops, instead of through so many screen layers. In effect, the air is surrounded by heated screens all sides, not just top and bottom like the ZP. The static pressure would be far lower than if it actually passed through so many layers of screen so the air flow would greatly improve the CFM from a given fan. We didn't have time come up with any viable alternatives for the return end, but we think it should be more free flowing. But at a 180˚ turn such as yours, air will bunch up, create a hot spot, which is less efficient. 

The overall point I'm trying to make is that you didn't have a preconceived idea as to how a collector is "supposed" to be. Without this crazy, offbeat, or "different" idea, I wouldn’t have brainstormed with Krautman. My brain is now working overtime as to how I could use screen loops as a simple way to form an effective absorber for my "next" collector. 

So thank you again dademac, for not only presenting an unconventional collector idea, but building and sharing your idea with others. And most of all reminding me that great ideas can come from the most unconventional thoughts.

 

Greg in MN

 

stmbtwle

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Reply with quote  #13 
Hmm that would be something like a cinefoil tube or downspout collector, only the "tubes" are made of screen, and it would work something like a ZP. Might work pretty well.
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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
dademac

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Reply with quote  #14 
Greg in MN

Yippee!! I love your ideas. The great thing is I can fiddle with the design on my own but of course it doesn't give you a side by side comparison. As I was building this I made the loops hap-hazard with the thought of what does it matter, all it is is a way for the sun to warm them and air to pass through. After picking your brain and that of your friend, I am realizing that there is much more to it.
.
I wish I could get an estimate of CFM on the panel. I do want to say that I tried a 12 volt computer fan. It did not move enough air. I tried a salvaged dryer fan and it moved too much air. I did not go look at the collector with the dryer fan running, but I would assume that most of the air passed under the screens. It does seem interesting to me though that when the dryer fan was running I would loose temp in the panel. The intermediate fan I am now using is a 110 v 6" industrial box fan. I have ordered an infra red temp sensor. It should answer some questions about where the heat is and where it is not.

I am very curious to see what the temp is doing at the corner. I was kind of embarrassed at first to show pics of the turn. One thing I have never added is I had some flexible black plastic lawn edging. That is how I made the corner so round. I then covered it up with tape of course. The loops on the corner I could have done much better on but at that point I was starting to see an end come to my project and got too excited to finish it properly.

I glued (silicone) and screwed the glass down, so it will be some work to open it back up. Next time I believe that I will just tape it around the edges then put the metal flashing back on. That will make it mush easier to make modifications.


stmbtwle

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Reply with quote  #15 
"It does seem interesting to me though that when the dryer fan was running I would loose temp in the panel."

Actually, with the fan running you SHOULD lose temp in the panel. The purpose of the fan is to move heat OUT of the collector (thus cooling it) and into your home. Otherwise what's the point? A hot collector by itself accomplishes nothing.

Admittedly getting the right air flow is a balancing act. You might try the dryer fan again, but with a speed control.

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

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Reply with quote  #16 
dademac,

I agree with Willie [thumb] and will add a few thought's. It is satisfying to stand by the output duct and feel a stream of hot air coming out. BUT those pesky laws of thermodynamics get in the way, heat naturally moves from hot to cold and the hotter something is the faster the heat wants to leave it. In other post's on this site they aim for a max temp of 120f with the proper air flow. Proper air flow can be found by swapping fans, using a big fan with a speed controller, or some have used a big fan and restricted the air flow with cardboard on the fan intake. The thing is to get the heat out of the collector before it has a chance to escape through the glazing and insulation. Ideally you want the output air of 85-95f coming out, you could run it cooler but then it may feel like a cold draft even though it is warmer than room temp.  Like Willie said it can be a balancing act to get the cooler output temps and not have the fan cycling on and off too much. It won't be as satisfying feeling the cooler air come out, but you will get more BTU's out of it in the long run.

Those IR thermometers are neat, a heads up it is tough to get accurate readings on shiny things or glass. To test that pick a target area on your glazing and move the gun from straight on to different angles.

If you are interested, you can see my little door collector here. I have two 24 volt computer fans controlled with a on at 90, off at 85 snap switch. And powered by two 7 watt PV panels, hooked up in series for 24 volts. The PV makes the fans variable speed, as clouds pass over the collector cools and the fans auto automatically slow down and speed back up when the cloud moves out of the way.
http://simplysolar.supporttopics.com/post/solar-heaters-in-frigid-temps-9608609?pid=1302771738

If you would, go to your profile and set the auto signature. Like Greg, Willie and I have. It will be added automatically when you click "Add Reply" Your general location on it helps us remember where your at what may be pertinent to your project. 

Thanks

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Gordy,
Minnesota
dademac

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Posts: 17
Reply with quote  #17 
Thanks Willie, Tampa Bay,

I will look into a speed control. I didn't know that you could use one on a 110v AC motor.
stmbtwle

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Reply with quote  #18 
https://www.ebay.com/itm/KB-Electronics-8811012-Solid-State-Variable-Speed-AC-Electric-Motor-Control-5/192353557905?
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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
dbc

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Reply with quote  #19 
dademac,  Welcome to the forum, and congratulations on completing your project.

I agree with others on the advantages of turning the screen so the air flow runs in line with the loops.  That would complicate the turn at the end, but for a straight-through design it would surely flow more air and would probably produce more heat.

A few years ago, someone here experimented with making screen tubes, with the idea of building a design similar to downspout or pop-can but with screen instead.  Part of the idea was to address the unequal air flow that plagued other tube designs.  I remember they had to figure out how to form the screen into consistent tubes; I think they stapled a thin strip of wood to one edge of the screen piece and rolled it into a cylinder, then stapled again.

Maybe you could make a screen loop absorber, like what you did, but form each loop with a piece of conduit or pipe which you pulled out after each loop was stapled to the frame.  Maybe set in a smaller pipe to form each valley.  You could also extend the sides of the screen frame up, and make a 'sandwich' with flat screens above and below the loops, or maybe just in back.  The whole absorber would then have a more consistent depth, and might be easier to handle during installation, etc.

Lots of interesting ideas to explore with your design.  Thanks, Don C.
gbwillson

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Reply with quote  #20 
I remember thinking of screen tubes when way back when Tom was making Cinefoil tubes a few years ago. Then Jeff tried to make some screen tubes here:
http://simplysolar.supporttopics.com/post/screen-tubes-7751325?trail=70&highlight=screen+tube#8

I like the idea, but long tubes are going to be much harder to make than shorter tubes. Then again, why would it be a big issue if each tube is short? It's not like screen is going to keep air contained within the tube. So short, foot long tubes, simply butted end to end should work fine.

Another thought is if I were to make 2" diameter screen tubes, and lay them on a raised platform of chicken wire. Next, place another layer of chicken wire on top of the appropriate height gap spacers (1⅜") to flatten the tubes to the optimal screen gap height. Not only does this create the proper screen gap, but the gap now has vertical screen "fins" to improve heat transfer. This is one of my many frameless screen ideas I have had rattling around inside my noggin. 

A continuous screen loop such as dademac's, might be tough to form accurately without some sort of template or form. Or you could make each loop from separate screen pieces. I have another idea as to how to form uniform loops, but I'll need to draw it up as it would hard to describe. 

Greg's brain is rattling in MN
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