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East/West facing roof - Page 2

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Posted by nicksanspam on May 23, 2004, 11:34 am
 


With some blade cleaning...


Seems kinda labor-intensive, with possible gaps and broken pieces.
 

Sounds better to me.


Styrofoam has a 130 F upper limit for full strength.


Looks OK to me.


Maybe not worth the trouble.


     = 2Pi16/ln(91/1.8) = 25.6 with D = 3', and kSdT = 1.7x25.6x48 = 2089 W.


Might involve some iteration.


Might help to make a few holes in the bottom of the pipe to let water out.
They use a double-foil "low-e line insulation" that comes in $0 12" x 62.5'
pieces and fold it over the pipe lengthwise and tape the longitudinal seam.
I wonder how long the foil facing lasts in the presence of dampness. Is
Reflectrix foil protected from dampness?


...in full sun.


Still thinking about the geometry. The max sun elevation where I live
at 40 lat is 90-40+23.5 = 73.5 degrees in June. You would think a 90-
degree wall wouldn't shade panels under and to the south at all, but it
does, because the sun is behind the wall in the morning and afternoon.
        
Nick


Posted by nicksanspam on May 23, 2004, 1:36 pm
 
An uninsulated pipe with a 130 F (54 C) surface temp and radius
r = 0.9 cm is buried D = 91 cm (3 feet) deep in earth that has
conductivity k = 1.7 W/mK. If the surface temp of the earth is
20 F (7 C), what is the heat loss for a pipe with length L = 10 m?

Using a shape factor S = 2PiL/ln(2D/r) = 2Pi10/ln(91/0.9) = 13.6 m
when L >> r and D > 3R makes kSdT = 1.7x13.6(54-7) = 1088 W.

...24 mm of 0.033 W/mK pipe insulation would increase r to 3.3 cm
and make S = 2Pi10/ln(91/3.3) = 18.9 and kS = 32.1 W/C in series
with G = 2PikL/ln(r2/r1) = 2Pi0.033x10/ln(3.3/0.9) = 1.6 W/C for
the insulated pipe, so it looks like the heat loss would be
(1/(kS)+1/G)(54-7) = 30.8 W, ignoring heat storage in soil.

Nick


Posted by LarenCorie on May 18, 2004, 6:43 pm
 Hello Simon;

Use your west facing roof (higher ambient temperatures,
and closer to your usage times).   Flush mount the panels,
so that they resemble big skylights, that will improve the
look, and value of your home, not detract from it.   Do not
mount the collectors on roof racks at weird angles. Instead,
just increase your recommended (for south facing) collector
area by 50-100%, depending on what panel module fits within
that square footage range.  The panels are just one component
of the whole system, so you will not be increasing the system
cost by nearly that proportion.

-Laren Corie-




Posted by mark schofield on May 19, 2004, 10:09 am
 I put two Grumman panels on my roof in 1980. facing south, roof is 45 deg
pitch.mounted them on 2x4 pressure treated sleepers to keep them up off the
roof, insulated the pipes and ran them to the basement. works like a champ.
an occasional leak in the parker-hannefin fittings to pvc piping, but no big
deal. But now, 25 years later, with the system going strong, its time for me
to re-roof. I'm 62 now, not 37. I'll have to lift or remove the panels
somehow to re-shingle. So now I wish I had them on the ground. I'd put them
in the garden and insulate the pipes well if you have the room and it won't
look bad.  Mark S



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