I'm glad to see someone thinks it isn't so stupid :-)
In this case I think new home builders are really conservative with trying new things due to the high price of houses and strict building codes.
And even though it’s a simple idea it’s the kind of thing HVAC companies would be happy to Charge you 20K for. Just like geothermal.
And I suppose it's really not so different from simply having a hot water heater like so many homes do? That you could program to only add more water to when electricity is cheapest? (And in-floor heating uses hot water pipes.)
But hot water tanks are very safe, they're only 60°C. I would think that 600°C sand (or rocks) is the kind of thing that's not particularly safe to have inside your home. That's really, really hot.
Have you done the math and figured out how many rocks a home would need, how much insulation, and so whether it's even viable in theory, setting aside practical engineering/safety concerns?
> Have you done the math and figured out how many rocks a home would need, how much insulation, and so whether it's even viable in theory, setting aside practical engineering/safety concerns?
No. But why wouldn't it be viable? And what could be cheaper than a box of rocks? No moving parts, other than a fan your HVAC system has anyway.
> But why wouldn't it be viable?
Because it would take up too much space at non-dangerous temperatures? Or would set your house on fire if compactly sized?
With a 30 degree delta in a system that uses 1MWh/month you could store 2 months of heat/cold in a 5mx5mx2m tank.
https://en.wikipedia.org/wiki/Trombe_wall
Coupled with a well designed ventilation system, a Trombé wall can also be used for cooling.
Basically commercial version of a box of rocks.