[Greenbuilding] Solar Water Heater architecture

[Lawrence Lile]

Corwyn, 

You are settling on almost the same architecture!

Here is the best way to get a tank of such a size:  A used Tote.  Totes
are polyethylene tanks in a metal cage, 250 gallon.  My local boneyard
sells them for $89.  They probably had some chemical or food in them,
most of what my local boneyard carries are food grade containers labeled
"Apple juice concentrate" or "Ginger oil" anyway they smell great.   The
tank is about 48"X48" X 36", and sits on a standad wooden pallet.  

>Here is my current plan (not done yet so take with a grain of salt).  
Water panels on the standing seam roof, mounted with S-5 connectors.  
Propylene glycol (with water, and neon colorant (to detect leaks)) in a
loop to the tank.  Probably an El-Sid or similar PV pump.  

Watch the head on your El-Sid pump.  They are low head pumps.  In my
system, the tank is near the roof, and I've got about 24 feet of pipe
round trip, add in some heat exchangers and elbows and I am just within
the El-Sid 10Watt capacity for pumping at 3 GPM.  They are also low
volume, you are considering a large system and the pump may need to be
larger.  

>Large site built 500 gallon non-pressurized tank 

That's a whole lot of storage.  Most domestic systems start at 50 gals
for two people, 80 gals for four.  But hey, if you are running, say,
radiant floor heat you might want 500 gals.  

>in the basement (possibly wood lined with glass).  Tank holds plain
water (with a different highly visible colorant).  I am hoping that I
will be able to detect a leak from solar loop to tank, or tank to water
supply. 

Here is how you detect a leak in your domestic heat exchanger.  Domestic
water is pressurized, tank is at atmospheric pressure with an overflow
pipe to a drain.  If you have a pinhole in your domesticv water, you
will start adding water to the tank and it will come dribbling out the
overflow pipe.  Arrange the pipe so you can observe it.  Viola'! 


 >More coils of copper tube to pre-heat DHW, and heat the thermal mass
(possibly also a hot tub to deal with summer excess).  The solar loop
should only have a few gallons, so that much glycol shouldn't break the
bank.  Wouldn't catch me with ethylene glycol anywhere near my drinking
water.

Agreed. 


>Open questions for me remain:
Can I get dyes that can be detected for both kinds of leaks?

Good ol'e food coloring.  Cheap, food safe (well, I don't eat it if I
can avoid it) You can think of two colors like yellow and blue that make
green if they mix.  If you get green water, throw the whole syustem away
it's fulla leaks.  

>Best method of building the tank (and ensuring that failures don't
result in a flooded basement?

Buy a tank. Plastic Tote.  Or buy ten 55 gallon plastic drums and build
a foam box around them. Avoid steel, and avoid homemade tanks. 

>Control systems? 

Mostly the El-Sid, with the photoelectric panel, is the control system.
If there is sunlight available, it tries tro harvest it.  Sometimes in
the morning it will actually cool down your tank.  But it either works,
or it doesn't.  If you have  a lot of sensors and brains then you have a
lot of things that will fail. 



 >I would like to be able to control movement of heat based on tank
temperature, house temperature, time of day, outdoor temperature,
season, occupancy level (and probably some others I can't think of right
now).

Don't bother.  Put a PV panel on your pump, and you are done. 

>Cost?

I'm going to have around $1000 in my system, with 50 gals storage, two
used collectors approx. 3' X 5' collectors, mostly built out of
scrounged parts. 
-Lawrence