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netttech

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Reply with quote  #1 
I conducted a test comparing cinefoil & black aluminum flashing yesterday. Both materials are flat, suspended with 1 1/2" space between the glazing & panel back. The panel is passive, with heat-shrink plastic as glazing. 

Below is a picture of the recorded temps. It also has the performance numbers of the same test conducted with 2 layers of black aluminum screen & cinefoil.

The cold air temp were taken via a old mercury thermometer. As in the previous test, the digital thermometers has a 1-2 degree accuracy difference between them.

You will notice the 102 degree entry of the cinefoil has a ? mark. I marked that because the thermometer had fell over & had some direct sunlight on it. I suspected it skewed the temp & the next reading confirmed the direct sunlight skewed the recorded temp.

Jeff
Central IL
Solar air & water

P2282664.JPG 

Bert

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Reply with quote  #2 
Jeff,

It's hard to read the image. Which one was the winner?


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Bert K.
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stmbtwle

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Reply with quote  #3 
It looks to me as if the flashing was running a bit warmer than the cinefoil, though I can't for the life of me figure out WHY, assuming all other factors to be the same. 
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Willie, Tampa Bay
gbwillson

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Reply with quote  #4 
If you click on the image it gets slightly larger. Looks like the painted flashing wins as it had slightly higher temps during most tests. It is the column on the right. How thick was the flashing and how did that compare to the Cinefoil? 

Greg in MN
netttech

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Reply with quote  #5 
Yea both materials performed very close to each other. The flashing may have a slight advantage but not by much.

As for the material thickness.....I don't know. I'm not sure if the cinefoil has a thickness label on it. It's heavier than typical household aluminum foil. The flashing for sure is thicker though. It's the standard flashing available at any home depot, lowes, etc.

It comes down to expense & which material you want to work with. Since I use the KISS method (Keep It Simple Stupid) on everything it proves cinefoil doesn't need to be in a tube form to produce good heat.

When I rebuild my window panel...I will likely use-up the rest of the cinefoil in the panel. If I don't have enough I will likely finish it with flashing since I have it on hand.

I cropped & enlarged the picture. Hopefully it's easier to read.

Jeff
Central IL
Solar air & water
edited results.JPG 


stmbtwle

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Reply with quote  #6 
Curious did you paint the flashing or was it already coated when you bought it? Im still trying to figure out the reason for the difference in performance.
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KevinH

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Reply with quote  #7 
There are various factors that could affect the results.

- I'm sure he tried to make the two halves of the collector identical, but it only takes a small difference to create different air flow, especially since this is passive.  One way to check this would be to swap the Cinefoil and flashing sides.  The temp difference should be the same.

- The collector would have to be kept exactly facing the sun.  A previous picture for the screen test showed it angled, but that may have just been for the picture (not tested that way).

- Cinefoil has a black coating on both sides.  Unknown if the flashing was painted only on the front.  If so, that means the flashing would be less emissive on the back (Cinefoil more emissive on the back).

- The black coating/paint is different (different absorption/emissivity).

Cinefoil is listed as 0.002" thick on some sites.  Regular aluminum foil is about 0.00063" and heavy duty is 0.00094".

Kevin H
MN
gbwillson

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Reply with quote  #8 
Jeff didn't mention what he used to paint the glazing and previous paint tests have shown enough variance between paints to say that more testing would be needed. Cinefoil has an electrostatic coating to absorb VISIBLE light. But no testing was ever done using other types of light, such as IR.  But if I was to make a backpass-type collector, I would likely use flashing, based not only on Jeff's test, but availability and cost. That said, Cinefoil has so many possibilities as far as different shapes that would be difficult, if not impossible to form with flashing. It's a lot like working with heavy paper.

Greg in MN

netttech

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Reply with quote  #9 
The flashing I painted & generally prefer Rustoleum flat black. Off hand....I don't know if the back side of the flashing is painted also.

Stmbl, There's very little difference in maximum achieved temps. Don't forget the thermometers may have a level of inaccuracy.

Another guess is the difference in the material thickness. The flashing being thicker, absorbs more? The temps stay pretty close until 40 minutes into the test & the flashing starts to gain more.

Airflow difference is a possibility. Being passive, its hard to tell if 1 side had more airflow from the heat generated or possibly the wind blowing that day. I noted on the sheet the wind is 10-15 from the west. That means the wind is coming from the left in the picture below. Colder air blowing in could have affected the thermometers. On the 3rd picture it shows the openings I cut-in to be able read the thermometers while it sits in the middle of the heated airflow.

Yes, the panel does have a slight angle towards the sun as you can see in the picture. It's not 90 degrees verticle to the ground or sun.

Both materials seem to perform well & apparently a little better than 2 layers of screen.

Jeff
Central IL
Solar air & water
P2272659.JPG 
P2272660.JPG  P2272658.JPG 

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