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Scott Davis

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Reply with quote  #1 
With side by side testing in mind, Gary and I originally planned to make the backpass our reference standard, but when we started testing, we found it had a much higher pressure drop (difficult to blow air through) and it didn't perform as efficiently as the screen.  When we discovered how easy the screen design is to build, how well it works and how it is easily duplicated, we went with the double layer screen design as the reference standard.

The backpass design we used only had a 1 inch air gap for the air when flashing was laid over the pattern shown below.  Increasing the air passage height and enhancing the design by adding "turbulators" may well increase the efficiency of the design.  More experimentation is definitely needed here!


Here are the steps Gary used to build the backpass design:

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


You can see the front of the backpass design in this short video.  It is just the design in the picture above covered with aluminum flashing:



Have you built a backpass solar hot air collector?  Please reply and tell us about it here!  Please be sure to include pictures if you can!

Do you have questions about the backpass 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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Take care, Scott MD

Garage_Hermit

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Reply with quote  #2 
Hi, All,

For what it's worth, here are a few shots of a Mini Solar Backpass Collector – it is the first (and only) collector I have made, finished a few weeks ago.

It has two baffles, one top, one bottom.  The plate stands on the lower baffle, which lies above the inlet port.  The top baffle also supports the thrust of the plate.  (I generally use this unit inclined against an open door).

Internal dimensions are 4 foot high by 2 foot wide, depth = 10 inches.

Basic construction is just a 30-mm styrofoam box, no rigid frame, as it is a "technology demonstrator", & has to go in my car !  I built it modular, so that the steel plate can come out and a hose-coil or radiator etc. can go in its place...  I run it with a shower screen (4 mm toughened glass), and the seal is just draft excluder and maybe a few bits of tape.

According to Scott's "Excel-ent" spreadsheet (!) this unit gives me spot-on 50 percent efficiency, so guess I cannot complain !

I built a heat sink/radiator on the back of the flat plate, comprising tubes filled with bird sand.

I had a great time building this, but will make a far better job next time !
I would encourage anybody to have a go at one, it is great fun !

Enjoy the shots !  (Got lots more when I can find them !) & feel free to ask any questions you want!

Bye for now,
Garage_Hermit

Attached Images
jpeg R_U_A_FAN_OF_SOLAR.JPG (680.84 KB, 355 views)
jpeg Mini_Solar_Backpass_Collector.JPG (742.05 KB, 357 views)
jpeg Mini_Solar_Backpass_Radiator_Rear_View.JPG (690.90 KB, 358 views)
jpeg Mini_Solar_Backpass_Test_inside_Vélux.JPG (663.79 KB, 348 views)


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(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...

netttech

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Reply with quote  #3 
My first test panel was about the same size. It was my eye-opener on the prospects of solar hot air. It looks like this fits inside a window frame?

There's nothing like feeling th hot air out of your 1st solar panel.

Jeff
Central IL
Garage_Hermit

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Reply with quote  #4 
"There's nothing like feeling the hot air out of your 1st solar panel."

Hiya, Jeff in Central IL !

Can't wait to prove you right !  I'm working at it , believe me !
I got a foretaste on Christmas Day - lunchtime, it was 12°C here, guess that is 54°F to you !
We got a couple of hours nice sun, and it was just too tempting, so I nipped down and bobbed my technology demonstator against the garage door, connected 3 meters of 5" PVC pipe to the offtake, and my cardboard-box office fan to the intake, and another 3 metres of PVC into the fan, and I pretty soon was getting 21°C (70°F) into my steel filing cabinet -- talk about triumph  !  It was better than all my Christmas presents put together (-:  (the garage was at 9°)...

So much SOLAR sloshing around in my head, can't do much else at the moment, still waiting to do the trial holes in my CEILING !
so watch this space !

bye 4 now,
Garage_Hermit
(great site, this !)



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(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
solardan1959

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Reply with quote  #5 
Garage hermit,
   That seems like a pretty big fan, was it on slow speed if it can be adjusted?Just wondering if you could slow it down a little to get the heat up to a more comfortable level.  Yes I know 70 is better than 50ish but maybe a smaller computer fan would get you enough flow but still get a more comfortable level of heat out.
By the way, your photos of your back yard looking more winterish?  People with real winter do not have palm trees :-)  (where about are you at in France on the Med?)
Dan
Garage_Hermit

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Reply with quote  #6 
Hi, Dan,
Agree about the fan, it was the only one I could get (requisitioned out of my office !).
It has two speeds, FAST and SLOW !  It also has a rotating head, but I lock the rotation OFF.
I actually had a great time, fairing that fan in and getting it to push air !
But I'll do as you say, and get a compter fan (in fact I bought one of these fans a few years ago and installed it in the PC, to boost cooling, in fact I had it working the wrong way until I realized !  Cost me 12 euros if I remember right, that must be 15.21 USD in real money !  After the PC fan, I will look at one of these little Solar PV cells they use round here on their boats, and a battery, then I'll REALLY be solar-friendly (-:

Ha ha, about the palm trees !  We see a lot of 'em around these parts, we live in Brittany, it is in northern France, just left of St Malo, so we are at 48.3° North, on the English Channel, opposite Jersey etc.  I guess there must be a little strand of the North Atlantic Drift that finds its way round here.  We also have some other strange plants around, like Viperine or guess Echium, now that is REAL solar, they come from the Canary Isles originally, guess some homecoming sailor must of dropped off a few copies, and they just spread.

I did the Big Trash Bag test on my fan, had to do it twice, as I got 78% efficiency the first time !
Then I realized I'd calculated for 100 liters, instead of 50, so that dropped me to bang-on 50% !  Had to repeat it 3 times, to make sure, that is a cute program that Scott came up with !

Nice talking to you !
GH


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(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
netttech

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Reply with quote  #7 
Congrats GH, you just experienced the SG (Solar Grin), that we have all had from our 1st panel. Once you feel the warm air the smile occurs natrually & hard to contain it. Yes the 'Solar Sloshing' is a side affect! All kinds of thoughts occur how to imrpove, make it bigger, hotter, less conspicuous, etc., etc.

No one told you that there is a Solar bug...did they.

Once bitten, it's an addiction.

I've been addicted to solar heat for 6 years now & still trying different things.

Jeff
Central IL
Garage_Hermit

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Reply with quote  #8 
Jeff,

I laughed my head off at that !

Thanks for telling me about the bug, now that it's too late !

Just before Christmas, we finally got round to changing a radiator - took it downstairs and bobbed it in the entrance lobby, it is at the foot of the entrance staircase. The difference it makes is astronomic !  Now I am installing a circulating fan in the basement, to slosh the air around more, these are just little things, but their effect also goes along way towards the SG.  Collectors are fine, but they also need Air Management, I guess that's where the other half of the secret lies !

Hope U have a nice warm SOLAR day (-:
GH

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(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
Spokes

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Reply with quote  #9 
Good Day,
I am very excited about getting started with a hot air collector. I watched a couple of Scott Davis's aluminum screen wire collector.  During the video's he also discussed the horizontal down spout collector.  A horizontal collector will be less obtrusive to the layout of my house and it seemed to be a reasonably priced and fairly easy place to start.  My hopes are to have it at least in the testing stage by late fall.  He covered most of the components with the exception of the fans.  they look to be an inline fan but more information regarding availability and rough costs would  will be helpful to work-up an estimated cost.
Thank you in advance for any and all information!
My first attempt at building a solar collector was about 30 years ago and I must admit it was a total waste of time and materials.  I attempted to build it with materials at hand and virtually no information or plans to go by, this is not a formula for success.  At that time the internet was not available so information was basically word of mouth or science/mechanics magazines so I really had low expectations.  Even store bought systems were not reliable, they had minimal engineering if any and often self destructed or didn't collect heat at all. 
I am sure that this time I will have a much better results mostly due to your efforts!  Thank you!!
I will try to keep good records (including pics) of the build and the end results and pass this along through this forum.
Keep building!!
Paul L
solardan1959

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Reply with quote  #10 
Spokes,
  You said "My first attempt at building a solar collector was about 30 years ago and I must admit it was a total waste of time and materials. I attempted to build it with materials at hand and virtually no information or plans to go by, this is not a formula for success."

   I would very much appreciate it if you could elaborate on the design and issues you had. While hopefully you can do better this time around it is always nice to know what did not work so well and what problems you had.

   Scott's downspout was also a big driving factor for me getting started along with Gary at the Build it Solar site.  Screen does not have to be 4X8 and I have had very good luck with longer narrower configurations.  Make sure you do a good browse around the side at different collectors and also look around Gary's site to see what may work best for you.  Also how much space do you have to work with?
Dan
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