Reading through Bob Ramlow's book, and came across a reference to high mass systems, where you heat sand rather than water or other fluid as the storage medium.

Has anyone had any experience with this?  The downside seems to be less control over how heat re-enters the house.

The only system that isn't flintstone technology that I've seen is what Radiantec did up in Vermont. They actually had the system documented by the DOE back in the early 80's and it supplied upwards of 90% of the energy required for that house over a year. Be extremely beware of claims by the renewables industry, most are not even close. Read Tom Lanes book, it's the real deal. Fluid is the best for storing energy when avail.

For an interesting low cost thermal storage system, consider the "Air Core" concrete masonry approach. There are two versions. One was developed and promoted since 1981 by the National Concrete Masonry Association (www.ncma.org) and only operates under positive pressure from a small blower, reducing potential moisture, mold and radon problems. The other approach patented by James Kachadorian but operates as an under-slab HVAC return air system which could pull in soil moisture and radon gas. More information is available in an ASME paper you can download from B.E.S.T. (http://www.energybuilder.com/ftp-resource.htm) -- scroll down page. Basic principle: extract stratified solar heated air high in the home, and route it into CMU cores. Heat is stored for later re-radiation up through the slab. Unlike a rock bed it does not consume extra electric power to discharge heat to the conditioned spaces. ~ Bion Howard

Recently came across this link: http://www.earthshelters.com/  which seems to provide a bit of a missing item vs. what I had previously thought about the idea of simply releasing heat under the house.  The concern I'd had was that the heat released under the house would move out and into the environment.  The insulating umbrella concept outlined at earthshelters seems to deal with this issue, and make it more viable to use the earth as the seasonal heat storage medium.

Anyone come across this before?  I got the link via here: http://www.gouingreen.com/