Posted by Redigoogle on May 17, 2006, 3:05 pm
Very interesting thread as I'm imagining a collector.
Can you provide or direct one to drawings?
Also, any comments on the use of black poly pipe
instead of copper. Copper $ is going through the roof right now.
And, someone recently cautioned me about the problem
of water boiling in the collector is using too small a pipe.
Posted by Jeff on May 18, 2006, 11:57 am
You don't want to use any plastics as they just aren't good conductors.
I had thought about making the manifolds out of CPVC to keep from having
to braze, but tossed that idea out as it would make repairs very difficult.
I think if you reread Mike's description through, he was pretty thorough.
How you hook up the sytem is up to you, but it looks like drainback
is the way to go these days. Least complicated and most reliable.
Posted by Mike on May 18, 2006, 11:39 pm
Sorry no drawings, but as the twinwall is 2440 by 1220 mm in size its easier
to make the panels sized to fit those measurements, allowing for a clearance
for expansion of the polycarbonate. I made my panels 2400mm height by 620mm
width by 130mm thick from 20mm treated timber then sealed with 2 pot epoxy
resin, finally painted externally to match the roof colour. Thus only a
minimal wastage from the twinwall and long narrow panels are much easier to
manhandle when walking around on the roof. I will make a hand drawing in
next couple of days and post it here.
I tried hi-density black plastic pipes as a experiment instead of copper on
one panel. It worked, but was only 50% as efficient as the copper one. Not
suitable for DHW heating, thought it may be ok for a swimming pool use
where the water is continually circulating by a magnetic drive pump.
Decided for pool heating it is easier to make a large frame to contain
several full size sheets of the aluminium corrugate mounted horizontally
with the plastic snaked from a top 1" header to bottom in several parallel
runs, to maximise water flow. Rather than cut backing strips its easier to
place another sheet of corrugate on the back and hold the springy plastic
pipe in place with some PK screws before setting the pop rivets. Allow
approx 8" at the sides to accommodate the bent pipes, no insulation or even
glazing is required if the water flow is high enough..
I don't use drainback or heat exchangers, our water is pretty good. In frost
situations the microprocessor senses the panel water temp and opens a dump
solenoid valve at the top of the panel, this clears out the near freezing
water and fills the panel with mains temperature water approx 15C. Same
thing happens if the panel exceeds 90C, the hot water is expelled. Whole
system runs off 12V dc/battery so continues to work if AC power fails. We
only get on average 10 frosts a year so not much water is wasted.
Question: Where can you purchase a magnetic drive DC pump that can pump to a
head of 4 metres as would be required in a roof mounted drainback set-up.
Only one I can locate is the Davies Craig generic automobile waterpump, it
would do the job but draws 8 amps @ 12 volts and only has a life of 2000
Posted by Gary on May 19, 2006, 1:01 am
These guys appear to have one:
"Build It Yourself" Solar Projects
Posted by samc on May 19, 2006, 9:08 am
12vdc magnetic drv pumps seem to ether be very expenceive or low head
like this one:
at the mo I plan to use a 110v brushed bear pump . it draws 1A at 12vdc
when running but will draw up to 10A when starting .