re: help!!! with solar energy
15 nov 1998
> for the structure, i recommend looking at the igloo ii dog shelter...
>$69.99 for the x-large unit for dogs up to 175lbs... heavily insulated....
an r10 cubical dogloo with a $12 thermostatically-controlled automatic
foundation vent in the floor might sit on top of a 4x8x4' tall platform
with 128 4-gallon square plastic tubs full of water inside, with 2 1.5"
layers (r15) of styrofoam all round and a 4x8' air heater with 2 layers
of r1 polycarbonate glazing with 90% solar transmission over the insulated
south side, and a shallow pond to the south, and a pv-powered 500 cfm fan
to heat the water tubs during the day. on an average december day in phila
it might collect about 4'x8'x0.9x0.9x1300 btu/ft^2 = 34k btu of solar heat.
with a water temperature of t (f) degrees, the platform might lose
6h(t-30)32ft^2/r2 for the south side over a 6 hour solar collection day,
18h(t-30)32ft^2/r16 at night, and 24h(t-30)112ft^2/r15 for the sides and
top, and supply 24h(70-30)80ft^2/r10 - 1k = 6.7k btu for the dogloo, if
the dog supplies 1k btu/day of heat. this makes t 91 f, after a long
string of average days.
with a platform time constant rc = r15/144ft^2x4096 btu/f = 427 hours,
it would cool to 70 f = 30 +(91-30)exp(-t/427) after t = -427 ln(40/61)
= 180 hours or 7.5 cloudy 30 f days in a row.