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re: question about building your own solar water heater.
31 dec 2000
wrote:
>just curious, has this design been built before?
>> you might start with a 12x12x4' deep plywood box...
probably not exactly this way. one of dr. william shurcliff's books,
"new inventions in low-cost solar heating: 100 daring schemes tried
and untried" (brick house, 1979) has a similar scheme s-96 on page 59:
"system employing water-filled bags on two-level roof equipped with
hinged plates that reflect, insulate, and also shed snow." he says:
h. r. hay's skytherm house at atascadero, california... was economical
to build and has performed excellently, according to the evaluation
reports by k. haggard et. al. of california polytechnic state university
at san luis obispo. it achieves 100% solar heating, and in summer,
near-100% solar cooling... it employs water-filled plastic bags on
the ceiling, and the bags are covered at night by insulating panels
that run on horizontal rails...
i propose a variation that is suited for use in new england...
employing several large crude mirrors, it intercepts 2 1/2 times
as much direct solar radiation (in new england in january) as the
atascadero house intercepts, that is, it has 2 1/2 times the gross
aperture. the "hot aperture," however, is much smaller; thus the
steady-state energy loss (whenever the panels are open) is smaller.
the panels are swung on horizontal hinges; tilting them upward tends
to dump off snow; their undersides are crude mirrors... i guess that
this system would provide near-100% solar heating...
each collection area employs water-filled plastic bags each of which
covers an area 36 ft. x 8 ft.; the thickness of water layer is 16" in.
above the water bags are two transparent sheets (held apart by air
pressure) that provide top insulation... the undersides of the panels
are crude mirrors and reflect much solar radiation toward the water-bags.
the panels include 3 inches of polyurethane-foam insulation... when open,
the panels are held rigidly at the prescribed angle by ropes... against
sturdy beams or posts. the panels are counterweighted for easy opening
and closing... when the panels are down, they comprise an almost-air-
tight enclosure, thanks to the inclusion of edge seals...
in about 1975 jonathan hammond built a house employing a solar heating
system somewhat similar... the reflector is opened and closed by means of
a hydraulic actuator. see passive solar heating and cooling, conference
and workshop proceedings, may 18-19, 1976, albuquerque, nm, report
la-6637-c by los alamos scientific laboratory; p. 153.
in about 1977 the farallones institute built a small house called
cabin b, with a somewhat similar solar heating system. see proceedings
of the 2nd national passive conference, vol. 1, p. 298. also solar age,
july 1978, p. 20...
there's nothing wrong with the technology, but practical solutions
require careful attention to economics as well as physics. for instance,
these days, hammond's house would probably be less expensive if it used
a small motor or a garage door opener or a satellite dish positioner
instead of the hydraulic actuator.
nick
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