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re: in the attic thermal solar collector
2 apr 1998
dr.jack  wrote:

>i've read several articles on using roof-top solar collectors to
>supplement the hot water heater or for heating a room.  here in
>texas, the summer time temperatures in my attic are extreme...
>has anyone ever attempted to place piping in the attic to utilize
>the excess heat that is trapped in the attic?

solar pioneer norman saunders, pe, suggests using enough 3" copper
(not cpvc, which he feels might burst under 100 psi city water pressure)
pipe to hold about 6 gallons of water. solar attic in minneapolis makes
attic heat exchangers. about $1,000. you might make your own with a $200
duct heat exchanger and high temperature fan or an old $35 auto radiator
and 12v fan near the peak of the attic, with a small pump and check valve
and pipe loop through the water heater downstairs, that turns on with
a heating thermostat in the attic in series with a cooling thermostat
at the water heater, or a differential thermostat. it may need some sort
of freeze protection, eg a small heater and thermostat attached to the
pipe below.

>how effecient would this be. 

that depends on the attic geometry and whether the south roof is
transparent. it's 123 f at the peak of my transparent attic today, with
the windows and turbine vents open, and no insulation in the north roof.
magicaire's (818 767-8333) all-copper 2'x2' 500 psi rated shw 2347
duct heat exchanger transfers 45k btu/hour between 125 f water and
68 f air at 1400 cfm, with a 0.1" h20 pressure drop, so it might heat
60 gallons of water from 60-110 f in about an hour, in a 125 f attic. 

>how cost effective would it be compared to roof-top solar collectors?

very cost-effective, i'd say...

nick




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