re: outdoor showers SOLAR.KnowledgePublications.com

re: outdoor showers
10 sep 2000
snowshoe@xyz.net (jan flora) wrote:

>if you *really* want to have a neat set-up, build a sauna -- a little
>shack with a woodstove. pile rocks on the stove. build benches, on
>several elevations in the shack. put duckboards (slatted boards, like
>pallets, but nicer) on the floor. build a dressing room out front,
>where people can dress/undress...

            4'            4' 
      ----------------------------
     |             |  b e n c h   |
     |             | . . . .      |      maybe like this from above,
     |             |              |      and 8' tall (in courier font.)
     |  dressing/  |       .  b   |
     |  shower     |          e   | 8'
     |  area       |       .  n   |
     |             d          c   |
     |             o       .  h   |
     |             o              |
     |             r              |
      ------d o o r---------------

a well-insulated low-mass version might use an electric hot plate vs
a woodstove. the walls might be an interesting cloth over 1/8" thermo-ply
hardboard or 2" foil-faced polyisocyanurate foamboard (eg atlas roofing's
energy shield or celotex super-tuff-f, which they say can withstand 240 f
indefinitely with no outgassing.)

with hardboard, the banya has about 8x0.125/12x4'x8'x50lb/ft^3x0.3btu/lb-f
= 40 btu/f of surface thermal capacitance plus 4x8x8/55 = 4.65 for the air, 
so heating it from 70 to 200 f requires about 5,800 btu, which might come
from a gallon of water changing to steam in a 2'x2'x4" deep ferrocement
tray sitting on top of the hot plate. the tray needs v ft^3 of 25 btu/f-ft^3
concrete to store heat, cooling from say, 512 f to 212 f, so 25v(512-212)
= 5,800 and v = 0.77 ft^3, about 3" of thickness. a 1500 w hot plate could
heat the tray in about an hour.

foamboard vs hardboard walls make air the main capacitance, so we can
heat the banya from 70 to 200 f with only (200-70)4.65 = 605 btu in about
7 minutes with a pint of water in a heavy pot on the hot plate, using less
than 2 cents at 10 cents/kwh. how can we make low-mass benches? hammocks?

with 2" r14.4 foamboard inside and outside and 6" r19 fiberglass in the
middle, keeping an airtight banya 200 f on an average jan -10 f day in
fairbanks requires (200-(-10))64ft^2/r47.8 = 281 btu/h, about 82 watts.

fresh air might come from a condensing air-air heat exchanger at close
to 100% efficiency, eg a couple of 100 cfm muffin fans at right angles
to a 1' coroplast cube.

nick