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re: solar attic
10 nov 2001
 wants to:

>...replace the south facing roofing with something kalwall.

kalwall seems to be obsolete for greenhouses. i made a kalwall trombe wall
in 1980, but replaced my 640 ft^2 south roof with "dynaglas" about 5 years
ago (with a $10 reroofing permit from our boca township.) dynaglas is
a single 0.020" layer of clear corrugated polycarbonate greenhouse roofing
material that costs about $1.50/ft^2, with a 10-year light transmission
guarantee and a 20-year expected mechanical lifetime. it comes in long
sheets that can be overlapped on 4' centers like corrugated metal roofing.
there are several manufacturers. rimol greenhouse systems in hooksett, nh
(, 1 877-rimol gh) sells a version made by co-ex corp.

my south roof has been through lots of snow and wind and rain and heat
(143 f in the attic) and golf-ball sized hail with no problems, but
i lost my state farm homeowner's insurance ("it looks different!")
nationwide seems happy. most people mistake it for corrugated metal
roofing during the day, but they notice lights (if any) inside the
attic at night.

the corrugated surface distorts light. i can barely tell the difference
between my neighbor's cows and sheep, 500' away. if your south roof is
steep enough (say 45 degrees) you might use a single layer of flat
polycarbonate instead, but that isn't as strong or leakproof, since
it has no overlapping corrugations. rimol sells replex flat polycarbonate
in 49"x50' rolls for about $300 plus $10 ups. dynaglas requires a truck. 

>insulate the southside floor and put up an insulated wall
>running along the ridge.  

no attic floor insulation now? you might add 2 simple skylights in the
floor near the ridge wall, and make the new wall reflective, with
a solar water heater below it. the wall might be a parabola, with an
insulated shoebox below, with a shallow pond with an epdm liner on top
of the shoebox and a flat polycarbonate cover over that. you could move
water up into the pond with a tiny pump during the day and let it drain
down at night. keep the shoebox full with a float valve (or 2 in series) 
and a gravity-pressurized hot water supply. this won't pin you to the
back wall of the shower, but it will encourage hot water conservation. 

>i want to add thermostatically controlled vents that will duct this heat
>down to the first floor.  

the skylights might be very lightweight panels, eg a 2'x4' layer of
polyethylene film stretched over a light wood frame, with well-oiled
hinges along the north side and counterweights. you might put a 4'
"industrial" (efficient) ceiling fan ($49 from home depot) under a
4'x4' duct that goes up to the attic peak to suck warm attic air
downstairs during the day while creating an attic vacuum that raises
the skylights. (this requires a reasonably airtight attic.)

the top of the duct might have a hole (or 3 holes) in the side with
a one-way damper, a piece of poly film hinged at the top that only
allows air to flow into the hole from the attic, with some chicken wire
over the hole to keep the film from flopping out of the hole in the
wrong direction. you don't want warm moist house to flow up into
the attic on winter nights. 

the attic space might be cooler and dimmer and more usable if you hang
80% black shadecloth under the glazing to make a mesh-type collector.
instead of flooding the whole space with 8,000 footcandles at 130 f, let
house air flow up from the skylights into the attic volume and up between
the mesh and the glazing (if possible), then out of the mesh-glazing
cavity and up to the attic peak where it returns to the house, warmer. 

good luck!


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