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Gary29355

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Posts: 10
Reply with quote  #1 
I have been closely following the debate over the screen fabric to be used as a collector and I consider that we need to encourage the air to pass over the collector material and perhaps the curved shape of the Venetian blind may create some turbulence (aircraft wing principle) which would provide more contact with the collector material (the blind itself).

Correctly built it could be possible to manually adjust the blinds to gain optimum flow rate...and if you wanted to reduce the impact in summer you could have black one side and silver white on the other and simply flip them over. Potentially the blind could be used as only one of the dual screens...just a thought guys and am sure someone has already been there and fond reason why this cannot work....thoughts?

Cheers

Gary UK

GaryBIS

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Posts: 243
Reply with quote  #2 
Hi Gary,
Its an interesting idea, and I'm not sure how well it would work compared to the screen collector.

One thought is that the spacing between the blind louvers is fairly large compared to the size of the holes in the screen, and this may let some air pass through the louvers without contacting them and this might reduce the heat transfer efficiency?  

Another thought is that the screen offers some airflow resistance (that is, there is some pressure drop as the air flows through the screen), and that this flow resistance tends to spread the incoming air more uniformly over the screen so that air flow through all parts of the screen and removes heat from the full screen.  The louvers may have less flow resistance, and this may result in more air flow through some parts of the louvers than others.  
But, to the best of my knowledge, no one has actually confirmed that there is enough pressure drop through the screen to spread the airflow as described above, so, it might just be a nice mental picture that does not actually happen.

It would be nice to do a side by side test of a two layers of screen collector with a louver collector.

Desoto Solar uses louver absorbers on their collectors and think they are the cats meow.
http://www.iedu.com/Solar/Panels/

Gary
netttech

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Posts: 720
Reply with quote  #3 
I'm betting it would perform comparable to everything else. As for the spacing between louvers, not sure that would be a problem.

My first hot air panel, I used aluminum flashing painted black. The overall panel was 5'T x 16'L, with 4 channels (16"W) to serpentien the air around. The flashing was installed in a slight rolling hill layout a 4" deep ductwork sized space.

Even though there were 2" of space between the glazing &/or the backing, it heated the air very well. I had a lot more open space than louvers, for sure.

Personally I'm only famimilar with one style of blinds, that hang from string mounted on the top of the window frame. How would you mount the blinds so the entire blind would hang, suspending the louvers? Are you considering a verticle style panel??

I always thought painting blinds black, install them in the windows, would be effective. I know there's always the debate about letting the sun heat internal mass inside the house is better. However, the majority of heat-loss is drafty windows, with either heat leaving or cold air entering. My logic is the blinds would heat-up, cause a natural heated air flow upwards. Any cold air entering would be heated before actually entering the room.

I'm single & considered painting a set of blinds to test my idea...but keep forgetting about it.

Jeff
Central IL
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Posts: 4
Reply with quote  #4 
I have a black, blackout blind at one of the bedroom windows. On a sunny day a simple thermometer shows the temperature can be 20-25*C warmer at the top. I'm planning on using a Venetian blind for parts come the warmer weather in an undecided air heater design. I hope one hole in the end of each fin will be enough to hang them vertically. The aluminium mesh is a bit more difficult to source and is much more expensive in the UK I've found.

If successful it will keep old aluminium blinds out of the land fill too
Scott Davis

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Reply with quote  #5 
Sounds like an interesting design banners.  Please let us know what develops!
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Take care, Scott MD
solardan1959

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Posts: 1,845
Reply with quote  #6 
I backed up a little to Gary's thread and read about that guy's Venetian blind type of collector.  That is a fascinating article with pretty wild claims about heat produced.  I posted this under Solar Web Page > Forums > General Discussion and Chat Page > Long Narrow Horizontal Water heater, (probably air to), but it applies more here.
"I have been studying this one lately and I find it really interesting but a a little finicky to make. Wonder how it might be adapted to screen. http://www.iedu.com/Solar/Panels/
 
"The zen of passive heaters". Basically this guy claims it would heat up a 30X40X9 feet ceiling shed to 80 degrees with no additional heat. He makes a couple of interesting points about heating air not the collector, a theory I have been spouted out a couple of times. Also his collector has no insulation though I may replace his divider between the hot and cold air with polyiso instead of plywood. Also since he favors horizontal metal slats, (like a blind), I wonder if small strips of screen at 45 degree angles like this /////////// may do the same thing. but it is worth really reading the whole article.
Dan
vondolgb

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Posts: 2
Reply with quote  #7 
Glad I found this forum. Members are open to sharing new ideas and supporting out of the box effort. With kids in college, i needed to find affordable solutions to keeping the home above 60F when the gas bill arrives in the mail. Each time I came up with an idea, i would find where someone on this forum had already tackled it. I'm now down to two collector designs, one would be heavy duty aluminum foil cylinders with mason jar rings at either end with flat black high temp spray. I also believe that heating the air and not the collector material may have better returns. The less mass on the black absorber,the better. foil cylinders also provide the outside barrier, like pop cans. 

My second choice and best would be the aluminum mini blinds. purchased white and sprayed flat black on one side. And to think I had an original idea. LOL. Needing a vertical collector on the south wall, that replicates as close as possible a window for curb appeal and happy neighbors, this might meet my design boundries. 

Benifits:
  - Cooler south wall since the collector is vertical with air gap between wall & house.
  - Blinds turned to prevent sun rays from hitting the black side of the slats.
  - Curb appeal. Looks like a window with blinds. 
  - Thin profile possiblities

Some options include black screen behind blinds and touching the blind edges. Provides better airflow restriction \ balance and extra solar energy capture. Controlling the airflow in the front of the blind between the twinwall and the blind to be 1/3 or less while the air flow behind the blind would be 2/3rds. Goal would be to keep the cooler air on the twin wall less disturbed.

One last concept I am trying to design against is the solar energy that is reflected off the absorbers. As it bounces within the collector, I need a way to absorb it and heat up a surface that airflow can take the energy from. A non-metallic like black felt against the back wall to catch the radiation energy. the fuzzier, the better. This might be a mute point since my twinwall is greenhouse grade and is likely reflecting some of this usable IR energy.

In closing, I want to think this forum. This community not only brings fresh ideas, results and guidance but also support for the many wives that are  troubled with "holes in the wall" and non-conformist activites. 
gbwillson

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Reply with quote  #8 
Welcome to the forum vondolgb. Where are you located? The reason I ask is that if you are near a larger city you might be able to get your aluminum blinds used and very cheap. See if you have a Re-Store in your area. They sell the leftover supplies and everything they tearout of a Habitat for Humanity house. Every time I go there they have piles of blinds. I would imagine since they have to fit a specific sized window, they wouldn't sell well and you could get them for a great price. I've also picked up a bunch of ducting and fittings as well.

Greg, MN

Link to Re-Store:

http://www.habitat.org/env/restores.aspx
vondolgb

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Posts: 2
Reply with quote  #9 
Thanks for the tip Greg. I live in Middle Tenn. i'll look into this. [smile]
Gee Whiz

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Posts: 10
Reply with quote  #10 
I was also thinking along the lines of aluminum blinds whether 1" or 2"

I don't see why the guy makes that holder to put the mini blind slats in.

Wouldn't he/we be able to extend the blinds as made and screw to the bottom and top. 

Thats the little piece we all throw away when we install mini blinds.  The base holder.

I also think they would be able to be angled to the degree you want. 

Black blinds can be ordered on line.
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