|
Sneak
Peak Video of the |
 |
Download
Over 100Meg of |
|
Sneak
Peak Video of the |
|
Download
Over 100Meg of |
a solar cave
sun, 30 oct 1994
rex roberts talked about caves dug into south-facing hills...
suppose cavepersons had had glass:
. ^
. | up
.
r10 earth at . south ==>
55 degrees f .
.
/ g if the enterprising caveperson had insulated
rc / g the inside of the cavern with leaves and
------------------g w g mud, until, say, rc = 10, and the daytime
| .----- . temp of the cavern had been 65 degrees f
| 20 x 20' cavern | . and the nighttime temp had been 55, and
| 10' tall | . he or she had desired to warm the cave
| | . for, say, 5 days without sun, with an
--------rf-------- . average sunnytime steady-state floor
|vaulted -- stone | . temp of, say 90 f, and mammoth skins
| ----- ----- | t . piled on top of the floor to make
|--- floor ---| . a sunny day r-value of rf (which
. . . skins could be moved aside to
. rc . . . decrease the r-value of the floor
. g during sunless times), how much
note that since .rc g glass area, ag, would have been
the upper edge of the . g ag needed, and what would rf and
glass is lower than the . g the average floor thickness t
bottom of the floor, the floor .aa g have had to have been,
stays warm during sunless times, . g ignoring the clerestory
because of this igloo-like heat trap. . g cave window, w?
(how did the caveperson insulate around . g
the edge of the floor?) g south ==>
.
the daily heatloss of the cavern would have been .
.
lday = (8 hours)(1200 ft^2/r20)(65-55) ~ 5k btu. 32 f outside temp
.
during sunny times, the sun would shine onto the .
absorbing surface aa, assumed equal to ag, and some .
heat would be lost thru rc to the earth underneath... .
.
the daily net heat resulting from each square foot of .
glass might have been on the order of .
.
eg = 1000 - 8(90-32)/r1 - 8(90-55)/r20 .
sun glass loss absorber back loss .
= 500 btu/ft^2/day .
.
so keeping the cavern warm might have required only about .
10 ft^2 of glass... a 3.16 x 3.16' single-glazed window, or .
an early sliding-glass door... .
.
the mammoth-skin floor resistance would want to have been about .
.
rf = (90-65)(400 ft^2)/(5000/8) = r-16. .
.
during sunless days, the skins would be moved around or a trapdoor .
in the floor would have been opened to reduce this, to get more heat .
out of the floor... .
.
assuming the floor would have had a minimum r-value of 1, per square foot .
(both sides), the required heat transfer rate would have been about 5000/8 .
btu/hour, from 800 ft^2 of floor, which leads to a minimum temperature .
differential, after 5 days, of about 1 degree f.
so if the masonry had held about 22 btu/ft^3/degree f, the floor thickness
might have wanted to be about
t = (5 days)(5000 btu/day)/((90-66)(22)(400 ft^2)) = .12'
hmmm. ferro-cement...
other improvements might include making the whole thing above ground, including
some throwaway diet-pepsi bottles filled with water in the floor, making the
absorbing surface a parabolic reflector, and making the floor a wall.
nick pine (nick@ece.vill.edu)
|
 |
|
|
