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Posts: 4
Reply with quote  #1 
It's probably covered somewhere here, but I missed it.

I am planning on making a flat plate collector using, as far as I know now, 4" dryer vent tubing.  There will be 5 input and five output.  This diameter may be too big, I don't know.

But here's the question.  My optimum face angle is 40 degrees.  Since this collector is going into a window, that makes the hypotenuse (or collector length) about 68 inches.  I can extend the collector face to about 90 inches, but that drops my angle down to 29 degrees - considerably less than ideal.

So.  Am I better off to go with the extra volume or the better angle?  Or just split the difference.


Rick H Parker

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Posts: 809
Reply with quote  #2 
If this is going into a window, I suggest you consider a classic design call the Mother Earth Heat grabber.
You could use the optimum angle, then if you need more collection area just make the collection area wider then the window.
You could probably improve upon the design by incorporating elements of screen collectors.

Rick H Parker
Kansas, USA
Electronics Engineering Technologist

Posts: 4
Reply with quote  #3 
Thank you, but I have seen this article aleady. It is 41 years old and doesn't address my question. Obviously, lateral expansion, if possible, would improve performance, but regardles of collector size, there must be a tradeoff - and a way to calculate it - between length and angle. Much has been said about the tradeoff between air flow and temperature which, to my way of thinking, is easily resolved using a variable speed fan adjusted for best performance. I would think by now that angle vs length is something that wojuld have been addressed.

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Posts: 2,448
Reply with quote  #4 

I don't recall anyone making such a calculation. But given the option of a larger size versus optimal angle I would go for the larger size. Reflectors, or even a bed of snow in front of your collector could help with overall performance. With the wider configuration, a fan will help a great deal as your convection flow may be limited. 

Another thought might be to duct the collector into the window via a duct rather than the top of the collector itself. This would likely give you more flexibility as to the angle and location of the collector. As an experiment last winter I routed the intake and exhaust of my system under a 3" slot under the bottom sash using a 2.5"x14" adapter. It worked quite well, with the only difficulty being the insulation of such an odd shape.

Greg in MN 
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