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Bert

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Reply with quote  #1 
This is an interesting article about elbows.
http://www.greenbuildingadvisor.com/blogs/dept/green-building-blog/stuff-i-learned-joe-lstiburek-s-house-part-2

Elbows_0.JPG  According to this article the inside of the elbow ( throat ) is the important part to be curved. 
Vanes are even better, but may be difficult.
The outside of the elbow ( heel? ) may be better square, which seems to go against what most think.



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Bert K.
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SolarInterested

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Reply with quote  #2 
Only had a quick glance at the article but it seems they didn't test an elbow with both a curved throat and heel. Isn't that the most common type?
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KevinH

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Reply with quote  #3 
It would have been interesting to see the result of a 5th design that had the vanes plus rounding one or two corners.  These are the rectangular trunk line ducts.  Some of the concepts could be applied to collector plenums.  For the round ducting most people use there isn't much you can do other than keep things as straight as possible and use sufficient diameter for the flow.

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gbwillson

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Reply with quote  #4 
The article above deals with larger rectangular ducts, like what you might find on the main trunk or return in your home, not the smaller round ducts like we generally use. Take a look at the return on a home forced air unit. It will normally look like drawing #2, but with the air moving in the opposite direction for an up-flow forced air unit. The air filter is usually placed just after the turn. 

Grrrg in MN


KevinH

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Reply with quote  #5 

Playing with this calculator for round duct  https://www.cdicurbs.com/ductcal  it looks like the most important thing is having the right duct size for the air flow.  For example, if you try to get 200cfm through 20 ft of 4" duct the loss is .56 inch water.  With 6" duct it is only 0.08.  Most of the loss will be in the collector itself (with proper duct sizing).

Next year I am going to modify the U-turn plenum in one of my new collectors.  I may try the turning vanes to see if there is a noticeable improvement.

Kevin H
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Bert

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Reply with quote  #6 
I remember someone on here at a tube collector, maybe a downspout. They had curves at the plenum going to each tube. Will have to find that thread and see how it turned out.
Not exactly the same thing but close.

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Bert K.
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KevinH

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Reply with quote  #7 
That was Eli's downspout collector.  It had continuous curves joining each duct in the U-turn.  That would be equivalent to ducting bent into that shape.

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Bert

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Reply with quote  #8 
That's the one.
http://simplysolar.supporttopics.com/post/elis-aluminum-downspout-hot-air-solar-collector-7786177?highlight=eli%27s+downspout+collector&trail=20

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Bert K.
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Bert

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Reply with quote  #9 
Quote:
Originally Posted by SolarInterested
Only had a quick glance at the article but it seems they didn't test an elbow with both a curved throat and heel. Isn't that the most common type?


I did read it again and found this paragraph.

"Increasing the size of the vanes and spacing them further apart reduces the effective length even more, but increases the difficulty of production and the potential for error in placement and for restriction if a vane comes loose over time. Using an elbow with smooth heel and throat and three full length vanes can reduce the effective pipe length to one foot!"

If that last sentence is correct, that's a big deal. It may be worth some experimentation.

Here's  another article on it:
https://buildingengineer.wordpress.com/2009/12/11/turning-vanes-necessary-component-or-efficiency-reduction-device/




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Bert K.
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