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re: newbie in need of help
3 oct 2000
ray smith wrote:
>the system is for heat and not hot water
why not make hot water too?
>the system will be located south of dallas tx.
near italy, tx (monolithic domeland) where seldom is heard a discouraging
word, and 1260 btu/ft^2 of sun falls on a south wall on an average january
day, with a 43.4 f 24-hour average temp and an average daily max of 54.1,
ie an average daytime temp of 49 f? nrel also says 910 btu/ft^2 of sun
falls on a horizontal surface.
>required btu storage 384,000 (5 days of clouds)
that's 76,800 btu/day. so... your house has a thermal conductance of
76,800/(24h(70f-43.4f) = 120 btu/h-f? sounds like a tiny house, or a
superinsulated airtight house with very few windows. you might heat it
with 675 kwh/month of electrical energy consumption.
>required glazing area 64 sq. ft.
that might collect 40k btu/day of heat at 50% efficiency. maybe the rest
shines in the house windows on an average january day.
>...can i excavate a hole and build a solar closet underground?...
no. solar closets (tm) live above the ground in a sunspace, and they have
an air heater on the south side that collects solar heat. you could build
an underground solar thermal store, but digging is work, and it's harder
to insulate underground, and the sun doesn't shine underground, and warm
air rises, so a thermal store above the heat source makes more sense for
collecting heat. putting the store below the living space makes more sense
for distributing heat. an ideal passive solar house might have a sunspace
on the ground with a thermal store above that and the living space above
that, on the 3rd floor...
>since the system will be located about 20 ft. from the house i will have
>to run pipes to the home... the length of the run from the system to the
>air ducts is about 50 feet. is this too long? too much loss?
sounds like your solar furnace will be out in the yard, 20' away from the
house, and the pipes have to travel another 30' inside the house to reach
the air ducts (?) moving warm water through a pipe over this distance seems
reasonable, especially since the loss from the part inside the house will
also heat the house. that part might be uninsulated.
this kind of backyard solar furnace seems uneconomical, if it only provides
heat for the house. you might also provide hot water, or use it for storage
or parking space, or a heated swimming pool, or a concentrating cabana with
no glazing and a parabolic north wall, reflective underneath, with a $10
polyethylene duct along the ground inside the north wall that's filled with
water during the day, and a $400 insulated 1500 gallon poly ag storage tank
vs all those drums.
>can i simply run a copper pipe through each drum as part of the heat
>exchange system?
storing 384k btu in water cooling from say, 130 f to 90 f requires
384k/(130-90) = 9600 pounds or 1200 gallons or 22 55 gallon drums.
running a copper pipe through each one seems like a lot of work, and
why use a heat exchanger at all, unless you plan to drink or pressurize
the water for showers? why not just circulate drum water, and protect
the pipes from freezing?
nick
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