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re: wire gage needed for 68.5 amp 240vac?
27 may 2005
bill c wrote:
>propane here in the florida keys is $2.88/gallon. one dealer came out,
>looked at our setup and said, "save yourself the trouble and go to home
>depot and grab and electric tank heater."
solar water heating is extremely easy in the florida keys. nrel says
1090 btu/ft^2 falls on the ground on an average 71.5 f december day.
you might enjoy a solar pond with a transparent cover and pressurized
plastic pipe for a heat exchanger, similar to the one described at
http://builditsolar.com
...2 layers of floating bubble pack and 2 layers of greenhouse poly film
might make 50k btu of 110 f water with a 130 f pond on an average day
with 0.8a1090 = 50k + 24h(130-71.5)a/r2, ie a = 294 ft^2. if it cools to
110 f over 5 cloudy days, rc = -5x24/(ln(110-71.5)/(120-71.5)) = 287 hours
= r2x62.33d, so it needs to be d = 2.3' deep.
an r10 floating foamboard version with a pump would be smaller. 0.8a1090
= 50k + 8h(130-71.5)a/r2 makes a = 78 ft^2. say 96 ft^2. if it's about
120 f for 5 days, 5x24h(120-71.5)96/r10+5x50k = (130-110)96d62.33 makes
d = 2.6'. a low reflective wall to the north could make it smaller.
nick
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