[Greenbuilding] Solar Water Heater architecture

[Corwyn]

On Aug 14, 2006, at 09:41, Lawrence Lile wrote:
> 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.

Lawrence,

The Tote sounds good; where might I find them (what is a boneyard?) It 
might even fit in the
place I have available for the tank.

> 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.

Right, I have about 25 of head.

> 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.

Most domestic tanks have lots of heating all day long.   My heat 
requirements, on a cold day, run about 15000 BTU/hour, at 100º 
temperature differential, that is 450 gallons.

> 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'!

That sounds interesting, but given that it is an open tank, it would 
seem that thermal expansion and evaporation would make it less 
sensitive than I would like.  Plus, I most want to detect a leak in the 
glycol system.

>> 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.

Food coloring is hard to detect in small concentrations.  Someone on 
this list mentioned a dye noticeable in parts per million (billion?).

>> 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.

I was thinking more of a catchment system under the tank.  I don't 
trust any tank, home built or purchased.

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

I would like the following:
1)  Pump running the solar loop whenever there is heat to be extracted 
(this may be possible with just the PV panel.
2) Pump running the floor heat whenever it is cold in the house, there 
is heat in the tank, and it is daytime (so there will still be heat in 
the tank for DHW).  This can perhaps be done by a programmable 
thermostat in series with a thermostat in the tank.
3) Pump or release valve to keep the tank from getting too hot.

Thank you Kindly,

Corwyn

-- 
Corwyn
Kermit didn't know the half of it...
http://www.greenfret.com/
corwyn at greenfret.com