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Posted by nicksanspam on November 12, 2005, 10:31 pm

GE lab tests so indicate. Maybe 2 vs 20 years.

Not PEX, IMO. Maybe 1/2" copper pipe in circular grooves under a Cu or Al roof,
with silicone caulk to increase the metal-tube thermal conductance.

An enclosed solar staircase might be useful, with 0.005" adhesive Cu or Al
foil over polyiso foamboard risers and foil-faced foamboard treads.


Posted by Jeff Thies on November 12, 2005, 11:08 pm
nicksanspam@ece.villanova.edu wrote:

Ouch! Then it would seem that for a trickle collector glass is
definitely the way to go.

I found references but no articles on this. Can you give a little more info?

  with 0.005" adhesive Cu or Al

I don't have a good "picture" of this. I'm thinking that the tubing
would be embedded in the polyiso with the adhesive foil stuck on top.
Stairstepped down with the tubing running horizontally (perhaps in
series). I could be completely off here... Is it difficult to black
chrome (selective coating) the copper foil, I remember in copper foiled
stained glass there was a solution that was simply wiped on (probably an

What about unglazed "trickle". Black roll roofing, with some kind of
diffuser every couple feet to even/spread the water flow? That may be a
crazy idea, but it is cheap!


Posted by gosolar23 on November 13, 2005, 2:23 am
 I talked to a canadian solar/fin collector.  I could do that, but that
is going to be 80 fin and tubes.  I don't mind the cost, but 320
braised joints!  Holly smokes,  If you have a 1% failure  rate per
year, that is 3 failures per year!

I don't know what you are proposing, but it sounds crazy to me.


How can Polycarbonate hold my water in Nalgene without problem and can
you point to the reference?   I talked to the Crystal lite people, and
they think that water puddles all the time on  their 'skin systems' and
they don't know of any failures.

any help is apreciated, thanks, Eric

P.s.  We could do traditional glazing, but code is a real bear in
Seattle and horizontal glazing is safety glass.

Posted by nicksanspam on November 13, 2005, 10:18 pm

At 40 N. Lat, it might look like this:

.   .   .   p        
.   .   .       o
    .               l
  2'.<- collector       y       Dynaglas
    .   .   .   .   .   .   c              
    .  foil-faced foam  .       a       greenhouse      S -->
                    .               r              
                    .                   b       roofing
                    .   .   .   .   .   .   o      
                    .   .   .   .   .   .       n
                                 1x3.               a
                    | D |           .                   t
                                    .   .   .   .   .   .   e
                                    .   .   .   .   .   .  
                                    1x3 |       L       |

Tan(73.5) = 2/(D/2) makes D = 1.18', and tan(26.5) = 2/L makes L = 4.01'.
Scaling so D+L = 4' makes D = 0.91' with a 1.54' vs 2' tall inner glazing.

The foamboard might screw onto notched flats in parallel rafters above
and below it, with an aluminum cap strip above and 1x3s below and
vertical collectors screwed to the 1x3 edges.

Aluminum flashing might work better than foil. Home Depot (sku 125467)
and Lowes (sku 17376) both sell Amerimax Home Products 24"x50'x0.018"
brown-painted Al coil stock for about $3. Make a jig by screwing 2 5' 1x3s
to a 2x8 5/8" apart, place flashing over the groove with 1/2" copper pipe
over that, pound for 30 seconds with a big rubber mallet, remove the pipe,
make 2-3 more round grooves, spread silicone caulk in the grooves, place the
2' wide flashing over 3-4 10' pipes, glue it down to 1" polyiso board with
more silicone with the vertical brown side and the pipes and grooves facing
south, to the right above. The fin efficiency should end up above 80%.

That might work better than plain copper.

No concentration, and lots of loss by evaporation, with low winter temps.


Posted by Gary on November 11, 2005, 3:15 am
 gosolar23 wrote:

"Active Solar Collectors and Their Applications", Rabl gives
a curve for fin efficiency.  While this is presented in the context of
  collectors constructed from tubes and fins, it seems like it should
apply fairly well to your case.

Here are some results for this curve:

Alum 0.0179 inch thick (26 gauge?), with a tube to tube spacing of 3
inches, and a heat transfer coef from the fin to ambient of 2 w/m^2-C.

gives a fin efficiency of 0.96

Steel 0.0179 inch thick, with a tube to tube spacing of 3 inches, and
a heat transfer coef from the fin to ambient of 2 w/m^2-C.

gives a fin efficiency of 0.86

Fin efficiency is defined as the thermal resistance of your fin to a
fin with perfect conductivity.

k for alum is 205 w/m-C
k for steel is 50 w/m-C

So steel is 4 times worse, but the fin efficiency depends on the
square root of of kt, so the damage is not as bad as that.

Note that the efficiency depends on the kt product, so if the
thickness ratio of the alum material to the steel material has the
same kind of effect as the thermal conductivity ratio.

Another approach would be to build a little test panel.  You could
leave the back of the absorber plate exposed, and just measure the
temperature difference between the valley and the ridge with an IR
temperature meter.  All sorts of other interesting things might also
be learned in this approach :-)




"Build It Yourself" Solar Projects

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