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re: "money" portion of the parabola
25 nov 2003
wrote:
>how do you decide what part of the parabola to build? i'm thinking in
>particular of nick's 16' high south wall shed with the kerfed 2x4
>parabolic roof and 4 foot trough.
duffie and beckman's 1991 solar engineering of thermal processes has some
discussion about truncating parabolic reflectors...
>i wondering if it is possible to reduce the cost by a third and still
>collect 90% of the heat of the original. it seems a lot of the sunlight
>in the original plan is hitting the ground in front of the trough and
>mostly being lost to the cold ground.
an attic version might collect hot air and daylight through simple
non-weatherproof skylights in the insulated attic floor...
>this might be done by tilting the y axis 15 degrees and/or just
>building the portion of the parabola that collects the most sun...
directing the parabola above vs at the southern horizon seems like
a good idea, as does tilting the south wall back from vertical, esp if
the trough contains grid-tied pvs so we want to avoid shading noontime
summer sun and maximize the yearly pv output.
>what y-axis do you use for your focal point anyway? i had been
>thinking the horizon, but it seems halfway between that and the noon
>height (for the middle of the heating season i guess, january?)
i've been doing calcs based on aiming the parabola at the horizon...
>also, why not just glaze directly over water and a pane at 45 degrees
>maybe from front edge of shallow trough?
sounds like that would eliminate the 2-3x solar concentration.
>i don't see how you gain anything by closing the end walls...
enclosing the space makes heat collecting more efficient.
nick
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