[Greenbuilding] [BULK] Solar thermal with sand storage

[Speireag Alden]

On 2008, Jan 08, at 12:37, Lawrence Lile wrote:

> Well, I can speak to the theory - sand is a terrible heat storage  
> medium
> compared to water - low conductivity, low specific heat, doesn't
> circulate due to temperature differences so no convective heat  
> transfer.
>
> On the other hand, it is a lot easier to build a sand tank that  
> doesn't
> leak, vs. a water tank. All you need is a plywood box.  You'd worry  
> less
> about contamination of DHW with glycol vs. a water tank.  I'd say  
> you'd
> need a lot more sand (by weight), and a lot more tubes closely spaced,
> to make a go of a sand tank.  I'm not saying sand would not work, just
> that it would not be as effective.

     What about trying to have the best of both worlds?  Embed 2- 
liter bottles mostly full of water in a quantity of sand, all inside  
a box.  Leaks would be no problem, since the moisture would  
distribute through the sand and vaporize until the bottle was empty.   
After a bunch of years you might want to take the sand out and check  
the bottles, but as long as you didn't heat them above the boiling  
point or the tolerance of the PET plastic, you shouldn't have a problem.

     The advantage is that you could introduce pipe into the bottom  
of the "tank" without having to worry about leakage at the connection.

     What do people think?  Laren?  You're the 2-liter bottle  
expert.  :)

-Speireag.