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Plug-and-play sunspace house and water heating

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Posted by nicksanspam on September 16, 2008, 4:52 pm
M writes (re inexpensive 100% solar house heating):

Plug-and-play sounds good, with the same radiator and controls, but
different amounts of sunspace glazing and heat storage, depending on
the house and the climate.

When last She spake to NREL, 750 Btu/ft^2 fell on the ground and 1030 fell
on a south wall on an average 29.7 F January day with a 43.2 F high in
Boulder. So a well-insulated house with a 200 Btu/h-F thermal conductance
and no window or internal heat gains would need about 24h(65-29.7)200
= 169K Btu/day of heat, or 847K for 5 cloudy days in a row.

A 1000 Btu/h-F radiator with water temp Tmin (F) could keep the house 70 F
if (Tmin-70)1000 = (70-29.7)200, which makes Tmin = 78 F. If the heat
storage tank contains P pounds of water at 140 F on an average day and
(140-78)P = 847K Btu, P = 13661, ie P/62.33 = 219 ft^3 of water, eg
a 3'-tall x 219/3 = 73 ft^2 tank, eg a 3'-tall x 9.6'-diameter folded
cylindrical polyethylene film liner inside insulation inside a $00
3'-tall x 15'-diameter inflatable EZ-set swimming pool.

With a dark mesh curtain to keep a sunspace more efficient and comfy and
an average 36 F daytime temp, a $ ft^2 of R2 south sunspace glazing could
gain 0.8x1030 = 824 Btu and lose 6h(70-36)1ft^2/R2 = 102, for a net gain
of 722 Btu/ft^2-day, so we could collect 169K Btu with 169K/722 = 234 ft^2
of sunspace glazing, eg an 8'x32' or 16'x16' transparent wall.

A 200 Btu/ft^2 house in Rochester NY (560 Btu/ft^2 on a south wall on
an average 29.1 F December day) would need 172K Btu/day, so the same pool
could store heat, but if 1 ft^2 of sunspace glazing only gains 335 Btu,
we might need 172K/335 = 513 ft^2 of glazing, eg a south house wall with
16'x32' of R2 solar siding (we could refine this with a simple TMY2

A frugal 600 kWh/mo (68K Btu/day) of internal electrical use would reduce
the glazing requirement to 104K/335 = 310 ft^2 and shrink the tank to
a 4'x8'x4'-tall plywood box or a 3'-tall x 7.6' diameter pool or a few
vertical 55 gallon drums in a ring with a liner inside and insulation
outside the drums. With more care, we might stack drums to make a 6'-tall
x 5.3'-OD ring.

From a junkyard, with a short guarantee and no installation labor, if
you can use any of several years and makes, eg Japanese radiators with
4-peg mounts. I've bought 1984 Dodge Omni and 1997 Mitsubishi radiators
with their 12 volt electric fans (20 watts in series) for $5.


Posted by nicksanspam on September 28, 2008, 10:02 pm

We could also make a tank with a folded EPDM liner inside a rectangle made
with vertical 55 gallon water drums, with 52.8 ft^3 of heat storage volume
for 2 4-drum endwalls + 37.2 ft^3 per pair of sidewall drums. If 219 = 52.8
+ 37.2N, N = 4.46, so 5 pairs of side drums would do, with 52.8+37.2x5
= 239 ft^3 in 18 drums with a 10'x16' folded EPDM liner.


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