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re: something i've been thinking about since 1968...
3 aug 1996
edwin sayre wrote:
>just do the calculations. for example, 2 ft. by 20 ft. is 40 sq ft...
i missed the beginning of this, but here in not-too-sunny philadelphia, we get
a yearly average of 1400 btu/ft^2/day of sun on a 40 degree tilted surface,
ie about 58k btu/day on 40 ft^2. a bare collector (eg "big fins" or an
amorphous silicon pv panel in an 80 f single-glazed sunspace, with insulation
on the back, with a front surface at 130 f, and a surface still air film
u-value of 1.5 btu/hr-ft^2-f, will lose about 8hr(130-80)40ft^2x1.5 = 24k
btu/day, and gain about 52k btu/day, for a net gain of 28k/day. if the
incoming water is 55 f, heating each pound of water to 130 f takes 75 btu,
so a system like this might heat 28k/75/8 = 47 gallons of water a day up to
130 f, and most of the waste heat might be used to heat an attached house
in the winter, in the form of warm air from the sunspace...
nick
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