[Strawbale] Hot water storage concept - insulation

[Sherwood Botsford]

Tom Oswald wrote:
> Hi,
> We are working out ways to store heat in water-mass for home hot water and limited/back-up space heating.  We plan to heat the mass by passive solar, fire-box, and possibly surplus PV.  We are considering using a concrete septic tank to hold the water in, even though it may not be the most green material to use.  We are considering placing the tank outside the foundation, under a deck, on the earth.  We want to avoid using foam insulation around and under the tank as it is not a green material.  We are thinking about using saw dust but are concerned about it getting wet.  We are seeking suggestions on how to do this most efficiently and most ecologically.  
> Thanks,
> Tom 
> North Stonington, CT
> 
> 


Tanks:

Check into getting used gas station storage tanks.  They are 
large.  20,000 liters or gallons comes to mind.  They
will probably have remnants of gas in them so will need some 
cleaning.

When you fill them, add an anti-oxidant to them to keep them from 
rusting out.

Used shipping containers ( 8' x 9' x 40' can be had for about 
$2500.  They are heavy guage steel -- about 4 tons of it.  Don't
know how much work it would be to make them water tight.

Don't circulate the water itself.  Put a few hundred feet of
tubing in the tank to act as a heat exchanger.

Consider vermiculite or perlite as insulation.

Don't heat the tank with PV.  Use PV to circulate water from an
active solar panel.  See builditsolar.com for a bunch of designs.

Depending on your climate, you may want to set up an option
to heat the tank with a external wood fired heater.  (We get the 
odd November when it's -20 C, and foggy most of the month.
Solar heating is like sucking golf balls through a garden hose
in those times.)

(It's ironic that north america is buying so much bulk stuff from
abroad that shipping containers are selling for less than their 
price as scrap steel.  Not sure why.  I'm guessing they sell for
the price of scrap minus the cost of shipping them to a place 
that can take them apart.  They are strong enough that it's not
trivial to crush them.  They don't nest becuase they are standard 
size. All the features that make them good shipping containers 
makes them too expensive to ship.  Go figure...)