Posted by Zombie Wolf on July 2, 2006, 4:20 pm
You are right about the energy iefficiency of this setup, and here is why.
The collector plates need to be flat BLACK in order to do a proper energy
conversion of the light energy coming in. the light energy coming in is a
short wavelength, and when it hits the black surface of the collector plate,
it is converted into long wave energy , which then cannot escape back out
thru the glass. The plates absorb the energy as heat. Now, if you use
something that is thermally favorable to heat conduction, like aluminum
flashing metal, and you have grooves in this aluminum plate that the pipes
sit into, It is relatively easy to form a good thermal bond with this, with
a little roofing tar in the grooves. And copper is a very good conductor of
heat. Testing was done on these collectors, and a simple test was to see how
long it would take the metal in between to cool off when water was run
through the pipes. The plates will go cold almost instantly, which would
indicate a very fast thermal transfer. the water coming out of the other end
of the tubing is quite warm, indicating quite a bit of heat transfer. The
grooves are 6 inches apart in this setup. 60 feet of 3/8 copper tubing is
used in the serpentine piping. You can make these collectors smaller, by
putting the turns closer together, but you will lose collector plate area ,
and that is really what gets the job done. That is what collects the heat
for us. Also, glass is not the most efficient medium for this, there are
many forms of glazing that are more efficient. Most glass has too high of a
lead content, and it will block significant light. look up Kalwall glazing
on google. The collector plates have 1 1/2 inches of double foil
polycyuranite foam insulation behind them in the box, to prevent heat loss
through the back of the box, which is the largest heat - losing surface of
The tubes themselves collect very little sun energy, since their surface
area is quite small. This is why the collector plates are necessary..
Posted by Jeff on July 2, 2006, 7:35 pm
Zombie Wolf wrote:
Interesting idea. What kind of roofing compound are you using and how
are you applying this?
And copper is a very good conductor of
Depending on the thickness of the plate, 6" is starting to go a bit far.
<URL: sel.me.wisc.edu/codepro/new_codepro.html />
Run your own simulation, if you like.
60 feet of 3/8 copper tubing is
Is that soft tubing?
<URL: http://www.kalwall.com/spec.htm />
Light Transmission: 0 to 65%. U values are rather remarkable though,
perhaps you mean a different product?
The collector plates have 1 1/2 inches of double foil
Posted by Zombie Wolf on July 2, 2006, 10:23 pm
I apply some roofing tar (the rubberized black kind) in the grooves, then
install the pipes in the grooves. I then cover the tubing with a thin layer
of the roofing compound, this makes a good thermal bond between the pipes
and the aluminum collector plate. The tubing is surrounded by the roofing
compound , and firmly bonded to the plates, since the grooves closely fit
the pipes.The collector plates are then painted flat black. It's that
simple. Nothing esoteric here.
Posted by Zombie Wolf on July 2, 2006, 10:29 pm
"soft" tubing ? No, it is regular thickness 3/8 copper tubing , which I
built a bending jig for. This is also nothing fancy. It took me about an
hour and a half to bend a serpentine tube for each of the collectors. The
jig ensures that the tube and groove spacing correspond exactly when
assembling. It is sort of a "reverse" image of the groove structure.
Posted by Mary Fisher on July 3, 2006, 9:01 am
<snip perceived flaws>
But why should that *amuse* you?