3 ms·
Dirt has an r-value of between 0.25 and 1 per inch according to some quick googling, so 10ft would be maybe R-60. Surprisingly, that's only equivalent to about
by dgacmu 1y ago
Dirt has an r-value of between 0.25 and 1 per inch according to some quick googling, so 10ft would be maybe R-60.
Surprisingly, that's only equivalent to about 10" of polyiso rigid foam.
What this project is really taking advantage of is the super cheap thermal mass. Dirt has about a quarter of the specific heat of water, but it is, literally, dirt cheap, and much easier to keep in place than a liquid.
- ted_dunning 1y agoYou can also have a temperature cycle of 600C with dirt. Water is limited to 50-70C so the dirt loses a factor of 4 in specific heat, but wins back a factor of 10 due to delta T. The net is dirt wins by a factor of 2.5.
- pfdietz 1y agoThe thermal conductivity of rocks (and, I presume, soils) also typically declines as temperature increases, falling by a factor of 2 or 3 at 600 C.