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Scott Davis

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Reply with quote  #1 
The empty black box solar hot air collector is simply that - an empty black box.  We wanted to see how much adding a heat absorber (which is just material that the sun strikes and air passes over / through to grab that heat) really matters.  It turns out it matters a lot!

Fortunately, once you have your black box, all you have to do is put two layers of screen in it and you've instantly transformed your lethargic collector into a high performance solar collector!

Here is more information on the black box collector from Gary's site:

http://www.builditsolar.com/Experimental/AirColTesting/BackpassCol/TestingFirstGo.htm


Have you built an empty black box solar hot air collector?  Please reply and tell us about it here!  Be sure to include pictures if you can!

Do you have questions about the empty black box solar hot air collector?  Please reply, this is the place to ask about it!  We will do our best to help!

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solardan1959

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Reply with quote  #2 

Here is my "pole barn heater test bed", you'll probably see it a lot.  The right bay is my dual layer screen standard now, but before I added the screen I tested it out as a "black box" collector.  The middle bay was a "reflective collector" for comparison to the black box.  The Black box did much better than I thought and put out more heat than I expected.  With about 100 cubic feet per minute flow (cfm), the recommended level is 3 cfm per foot or 96 for this panel, I was getting over 84 degrees out of it with enough airflow to heat several rooms, (the input and outside temp was around 35 degrees).  It was very close to the output from the far left downspout collector with nothing in it.  The depth of this collector is 6.5 inches to the insulation, 7.5 overall, and I use twin wall poly for glazing. (each collector is 4X8)
   The reflective box put out about 65 degrees, it would be better than freezing but a coat of paint or two layers of screen will do wonders.  (it then went to 102 degrees output with just screen)
Dan

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911Seven

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Reply with quote  #3 
I some how found a link to one of your down spout collectors, and became hooked on the idea of using solar to assist with heating my home.  Just recently building a new home, I now have a full basement that I never had before and am looking forward to working on so many projects that have been put off.  Of course the hot air heater is in the basement, but all ducts go up to the living space, and I really don't want to run it to warm the basement, thus the hot air collectors I have found on this site really interest me.

My first thought when reading up on the down spout collectors, is why not use the single wall, aluminum flexible ducting.  It is about $1.40/ foot and comes in 50 foot rolls.

Then I found the black box collectors and the screen collectors.  Now I am more confused then before and of course have more questions.

Which is more heat/$ spent?  Down spout, black box, screen or even my idea of flexible duct?

Then I got to thinking, we have a surplus/scratch and dent building supply store near by.  So my thought was to use a 6 foot wide sliding glass door set for the glazing, and then use the 6 foot wide screen doors for the screens in the collector.  While it may cost a little more, it is readily available and may be easier to build into the project.  Will I need to make sure the screens are black metal and not fabric?  Will the door set be sealed enough to work?  Properly placed on the side of the house, it could look like an ordinary door.

What kind of performance can I expect from a roughly 6 foot by 6 foot three screen collector?  I know there are a lot of variables.

I live in NY, near the VT and Mass border, so it does get cold here.  Unfortunately this will be installed on a South/East facing side (a true south facing alternative is not close enough to the house) of the house, but a few feet away is a steep snow covered hill.  I hope the hill and snow will reflect enough sun back during the evening when the sun is on the other side of the house.
solardan1959

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Reply with quote  #4 
911,
   Look around Builditsolar http://www.builditsolar.com/ under the projects section and hot air collectors.  A little bit of reading there will answer a lot of your questions more in detail.  Gary has an example using the flexible duct, it works but is not even close to the best option and is expensive.  Screen can be had for your 6X6 for less than 35.00 dollars.  I have a very similar collector on my kids shed that uses natural thermosyphoning but gets shaded a little to much.  I just wrote about my garage heater again 3X5 double glazed, and it's working real well, in the Forums > DIY Solar Experimentation & Performance > Side By Side Testing for Hot Air Panels section, or click here:
http://simplysolar.websitetoolbox.com/post/Side-By-Side-Testing-for-Hot-Air-Panels-6086998?trail=30
there are so many options, take a little time check out the different options and go with what you think will work best for you.  Two or three layer screen is hard to beat and believe me, I've been trying.
Spent quite a bit of time in your area, know it well, It's a nice place to live.
Good luck, Dan
Scott Davis

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Reply with quote  #5 
I agree with Dan.  So far, the double layer screen is the best performer, cheapest and easiest to build.  While the black box is easiest of all, Gary and I both independently found it to be the worst performer by far.  It's a simple matter to build a black box and then add two layers of inexpensive screen, readily available at Home Depot or Lowes.

i didn't even bother to graph the test with the black box because it was so poor.  Here are the results from the side by side testing here.  Gary also experience similar results from his house in Montana.

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netttech

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Reply with quote  #6 
I believe Sliding door glass has somekind of treatment. It affects (blocks??) the sun as it passes thru.

I'm sure someone knows more about sliding door glass than I do.

SLiding doors are generally pretty heavy, so keep that in mind, when building the frame/mounting.

I'm biased on screen also. I've had both screen & down-spout panels, but the screen is cheaper, easier to work with. I used charcoal colored screen & lightly sprayed cheap flat black paint on it. 

Performance tends to favor screen also. However the performance difference between the two panels I had (screen & down-spout), was very little. I changed from down spout to all screen this year. My panels are window units, mounted in 2nd floors windows, so being light-weight is better.

Jeff
Central IL

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solardan1959

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Reply with quote  #7 
   I passed up on some new beautiful white 3X7 door like fixed window panels that Menards had.  They got a special deal on them from Las Vegas for 50 dollars each.  They were heavily treated for UV and blocking the desert sun.
   Many people including me have used sliding door panels with good results but unless the were dirt cheap I probably would not pay for them.  It's to easy to find used glass panel being given away.  Jeff is right on all points and the biggest is glass doors can be very heavy.  They need a heavy frame and several people to mount, though somehow I always managed.  Also with used glass the the UV protection is probably unknown.  My favorite is twin wall poly as it has a known light transmission, is light and easy to cut, manage, etc......But glass looks good and can last a long time....

  We really need to move this conversation to another location as it seems like we have moved beyond the Empty black box collector.
Dan
911Seven

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Reply with quote  #8 
Thanks for all of the replies and feedback.  The gears are turning inside my head now, and I can't wait to get this project started.

2 screen and the plastic panels from Home Depot it will be.

I will document all progress and update with details as the project progresses.
Scott Davis

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Reply with quote  #9 
Super 911Seven, we are looking forward to seeing your updates!  Please be sure to take and share lots of pictures!
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Dutch

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Reply with quote  #10 
So, Scott Davis, instead of using aluminum downspout as you did in your Youtube video of Oct. 2010, you get as much heat output using dark-colored screen to collect the sun?  If so, how big of a box did you use and how do you input basement air into it?  I understand how the downspout box works, and was all ready to build one, and now I read about this screen/double screen stuff which seems much lighter/more portable (I'll store mine in the garage over the summer) and seemingly easier to build.  I assume the inflow must be forced through the screen, by maybe installing the screen diagonally and having the inflow  and outflow connections on opposite sides of the screen?

Let me know what you think, even if I'm WAY off.

Thanks,
Newbie Dutch
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