Posted by Mandy on April 4, 2004, 4:08 pm
Having read many of the posts in this forum, I can predict a great number of
rolling eyes and long sighs while reading this question... your knowledge is
vast and technical, and I stand before you humble, and curious. Please
complete the following statement:
A simple collector is best made of ______, and size (thickness) ______
I plan to build a small solar water heater, using copper tubing mounted to a
collector plate, and need to know how effeciency is affected by the
thickness of the tubing walls and collector plate, and material of the
Thanks in advance.
Posted by Cosmopolite on April 5, 2004, 12:15 am
The thinner the copper is, the faster the heat tranfer to your fluid.
When calculating for the collector plate, the thickness is the distance
from the tube to the edge. If the plate joins two tubes, it would be
the middle distance to the tube
Posted by Gary on April 22, 2004, 8:03 pm
Not sure if your still watching, but I ran across the following material
that might help with your question:
The numbers in the table below indicate the efficiency of the collector
plate in transfering heat to the collector tubes -- 1.0 is perfect:
Tube spacing in inches
3 inch 7 inch
0.04 thick Copper 1.0 0.93
0.02 thick copper 0.98 0.89
0.04 thick alum 0.99 0.92
0.02 thick alum 0.97 0.85
This assumes good thermal contact between the tubes and the collector plate.
I think copper is a good material for long life, low corrosion etc.
It looks like you don't pay much of a penelty in efficiency for tube
spacings up to 6 or 7 inches, and collector plate thickness down to 0.02.
Posted by Sonideft on April 26, 2004, 11:47 pm
Hi Mandy and group:
Our company is a distributor for Solar Thermal panels from Thermo Dynamics.
They have some of the most advanced panels in the world and have over 20
years of research and experience. Their panels use an aluminum fin about
5.5" wide and 0.02" thick. There is also a copper tube that is
metallurgically bonded to the aluminum fin so that there is high heat
conductivity and no chance of corrosion between the two metals. You can see
more details of this in the following document:
www.heatwithsolar.com/products/G_Series_tech.pdf The end result is a
collector with an efficiency FR value of 74%, which is pretty good for a
I mention these things so that you can get an idea what the big
manufacturers are doing. Hopefully it will be helpful in your project. In
our support for the hobbyist, we can sell you the fins we use separately and
you can construct them into collectors and arrays. In Canadian $$, the solar
fins sell for $6 per square meter and solar fins assembled with 3/4"
headers (4 ft x 8ft) sell for $57 each. Hope this information is helpful
without sounding too much like a sales pitch.
Stephen Cumminger, P.Eng, MBA, MCPM
Posted by Duane C. Johnson on April 27, 2004, 12:45 am
That's a bit misleading.
Your 74% efficiency number, while technically true, is not
very useful as the temperature rise is zero degrees C.
What is the efficiency of your collector
at a more useful temperature rise?
Let's say the temperature rise is 60C (108F):
50C (122F) average water temperature.
-10C ( 14F) ambient temperature.
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