|
|
re: parafin and solar thermal storage-non building
31 may 1997
dsg wrote:
>cost vs storage: do esoteric compounds,
>compare favorably/obtainable to parafin?
water compares favorably.
>this is not for high temps such as "molten salts."
>storage method for 240 therms over 16 hours
>suggestions appreciated.
let's see. storing 240x10^5 btu with a 50 f temperature swing requires about
a half million pounds of water, about 7,500 ft^3, eg a 20' cube, eg a small
version of the 40' deep x 82' wide x 700' long epdm-rubber-lined methane
digesters costing 0.02 cents/gallon (including excavation, at 1976 prices),
described in us patent no. 3,933,628. a 20' cube of 200 f water surrounded by
r20 insulation in 70 f air would lose about 16(200-70)6x20x20ft^2/r20 = 250k
btu in 16 hours, cooling by about 250k/(20^3x64) = 0.5 f.
>is the ground an insulator or a heat sink???
it's not a great insulator, with us r-values ranging from 0.06 to 0.24 per
inch, according to fig. 6 and table 7 on page 22.13 of the 1993 ashrae hof.
it's better when dry, and better for downward than upward heatflow, since the
main mechanism for upward heatflow is evaporation in lower soil layers and
condensation in layers above, which is one reason it's hard to keep soil dry.
nick
|
|
