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Posted by sam c on August 30, 2008, 7:21 pm
 
Anti-Spam wrote:

hi mark
having now made 2 panels I can tell you my method :
I use heat spreader plates (for timber under floor heating) for the
collector plate , 15mm copper for the risers and 22mm copper for the
headers . the tube plate bond is completed using silicone chalk or a
setting heat transfer silicone . for plumbing of risers to headers I use
lead free plumbing solder with fittings but brazing is generally
recommended to stop the possibility of leaks after a stagnation situation

I assume you know of the yahoo solar thermal group .

sam c.

Posted by gary on August 31, 2008, 3:48 am
 

I guess this depends to some extent on whether you are doing a design
that is going to be used for making a large number of panels (ie going
into production), or a few for your house.

If its a few for your house, here are some thought:
- I've been using aluminum sofit material -- its about 0.02 thick
(which is about right), and it comes with some shallow grooves already
in it that can be expanded to fit half inch copper or PEX pipe.
Some details on doing this here:
www.BuildItSolar.com/Experimental/PEXCollector/PEXCollector.htm
(most of the details on the Construction page)

- I've been concentrating on getting as tight a fit as possible and as
much of a circumferential wrap as possible of the aluminum over the
tubing.  The remaining gap is paper thin when you do it right.  I've
been using ordinary silicone caulk to fill this very small gap and
provide a thermal bond.  There are silicone caulks that are filled to
provide better conductivity, but I don't have the brand at hand -- it
is available in Europe.
Silicone is flexible, and will accomodate some thermal expansion
differences between the tubing and the fin.  Epoxy might not be as
forgiving this way -- but, I don't know for sure?

- You can buy some very nice extruded aluminum fins that snap onto
copper pipe -- these are made for radiant floors.  One outfit that
makes them is Radiant Engineering.  I've tried them, and they snap on
very nicely and fit well.  They are pricey.
http://www.builditsolar.com/Experimental/CPVCCollector/cpvccollector.htm

- I've done some testing of small sample panels with copper fins
soldered to copper pipe compared to various combinations of aluminum
fins and copper or PEX pipe with groove approach described above.
I'll put the test material up on BIS when I finish, but the tentative
answer is alum fins with grooves that fit tightly over copper pipes
with silicone between do quite well -- nearly as well as copper -
solder - copper.  The PEX does less well, but still quite good --
certainly more cost effective than the all copper combination on a $'s
per BTU basis.





You might look on this page:
http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm
and search for "Kris's Collector" he has some examples of doing a good
job of drilling headers and attaching risers.



Having an extrusion die made and satisfying the minimum order is
pretty expensive.
There are tons of existing extrusions out there -- you should be able
to find something.

Some people use galvanized metal sill plates that are intended for
metal framed buildings.


I think a regular rotary miter or cutoff saw would work fine.

Gary



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