Using Sand to Store Solar Energy

I've been a high thermal mass fan for a while. But I have to admit this article has me wondering a bit http://www.greenbuildingadvisor.com/blogs/dept/green-building-blog/using-sand-store-solar-energy
Both Martin Holliday and Mark Sevier make some interesting points. Anyone have a counter example with numbers?

Jim Argeropoulos wrote:
I've been a high thermal mass fan for a while. But I have to admit this article has me wondering a bit http://www.greenbuildingadvisor.com/blogs/dept/green-building-blog/using-sand-store-solar-energy
Both Martin Holliday and Mark Sevier make some interesting points. Anyone have a counter example with numbers?

This is very similar to a project that was on This Old House years ago (Bob Villa era). There was a group in Maryland that was building well insulated modular homes. To help with efficiency they buried a large water tank under the basement slab. They insulated the tank from the basement floor. They would run the water through a water to air heat exchanger. They could heat their house as well as cool the house utilizing this method. I'm not sure that sand is a real good source for storing heat. I believe that water is much better.

You may want to look up that old episode of TOH.

  The specific heat of sand is .2  which is 1/5 that of water. If you can get a good recycled tank at reasonable cost the heat storage and mobility using a water system would be far more efficient and reactive to management since convective flow and conduction constantly brings heat to areas of loss.