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re: graphite and heat storage materials useful with an air collector system
26 nov 2000
graham parkinson wrote:
>even though you derived it for rock/air thermal conductivities the criteria
>of storage surface area >10x the collector area sounds like a useful guide.
this has more to do with the airfilm-to-mass thermal conductance than the
type of mass... you might gain 300 btu/h from a square foot of glazing in
full sun. putting that heat power into 1 square foot of mass with a slowly-
moving airfilm thermal conductance of 1.5 btu/h-f requires the air to be
300/1.5 = 200 f warmer than the mass, which makes the air in the collector
very hot, so most of the heat is lost to the outdoors through the glazing.
with 10 ft^2 of mass, the air only needs to be 20 f warmer...
>how about a heat pit in the basement of 3" pvc (or salvaged copper) pipe
>sections on end, filled with water (and antifreeze...
sounds interesting. seems to me you should be able to keep these pipes
in the basement from freezing, or just allow some airspace at the top.
>the capped pipes could be stuck a few inches into in a slab poured over
>insulation on grade and spaced in a honeycomb pattern at say 2-3" spacings.
>the top ends could be in thermal contact (embedded in?) the upper slab
>forming the floor, even with mettalic or graphite rods carrying heat into
>the sunspace floor of the main story.
sounds complicated. you might prefer a reflective concentrating solar attic
with a polyethylene duct collecting trough and a low-power pump and a few
big plastic agricultural tanks in an insulated room and a few fan-coil units
or a hydronic floor for heat distribution. the underside of the north attic
roof could be lined with nielsen's 90% reflective mylar ($0.09/ft^2 in 4'
wide rolls from http://www.snomo.com/mylar.html) on smooth sheathing attached
to parabolically-kerfed rafters. you can efficiently collect high-temp water
that way and pressurize it for showers, etc.
most of the sun's energy arrives in beam form over a few clear hours per
week in cloudy places like seattle, which has an average of 0.8 kwh/m^2-day
(about 0.8 hours per day) of collectable beam sun for a 1-axis ew tracker
(or solar trough) in december, vs 1.4 on a 60 degree south-sloped surface.
what are these numbers for your location?
nick
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