Sand Bed Heat Storage for Solar Home Heating Systems

Heat storage for solar home space heating systems is normally done with a large water tank.  The water in the tank is heated by the solar collectors, and the heat is then drawn out from the tank when needed to heat the house.

Schematic of a sand bed heat storage system.

 Another alternative that is gaining some followers is to store the heat in a sand bed located directly under the house.  Most commonly the sand bed extends under a large part of the house and is typically a couple feet thick.  The bottom and edges of the sand bed are insulated from the surrounding dirt using rigid foam board insulation.  The house floor slab is often poured directly over the top of the sand.  PEX pipes are run through the sand and water heated by solar collectors is circulated through the coils in the sand bed to heat the sand.
Pretty simple.

The potential advantages of this approach are that its very simple in that there is really no heat distribution system required -- the sand bed directly heats the floor slab.  It also allows quite a bit of storage at a relatively low price.  It allows enough storage that for a very well insulated home, its possible to store up a bit of the winter heat needs in the sand bed in the fall. 

One unique feature of the sand bed storage scheme is that the living space is directly coupled to the heat storage.  This makes the system simple and basically eliminates the need for a heat distribution system, but it also means that there is less control of heat transfer from the heat storage to the living space.

There is not a lot out there on sand bed storage, but I've collected what I could find on this page....

The recent article in Solar Today on sand bed storage got me to thinking and running a few numeric checks, and I have to say I'm a bit skeptical of some of the claims made for sand bed storage in the article.  I've included these thoughts at the link above, and would appreciate your thoughts on them.  If you have experience with a sand bed storage home, I'd love to hear about it.


Gary