Plug-and-play sunspace house and water heating
nicks...@ece.villanova.edu
>Is the plan to have this eventually be a manufactured, packaged,
>plug-and-play sort of system (definitely the way the market is going)
>or does it always need to be custom designed?
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.
>Boulder is doing a big retrofit push to meet the goals of the local
>Climate Action Plan. This might be one way to go if it's simple to
>understand, engineer, and install. God knows we have lots of sun.
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 =3D (70-29.7)200, which makes Tmin =3D 78 F. If the heat
storage tank contains P pounds of water at 140 F on an average day and
(140-78)P =3D 847K Btu, P =3D 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 $200
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 $2 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
simulation.)
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.
>And BTW, I have a cracked radiator in my Honda CRV, which will cost far
>more than $35 to replace. Where do you get a radiator for $35?
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 $35.
Nick
nicks...@ece.villanova.edu
>insulated house with a 200 Btu/h-F thermal conductance and no window or
>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
>tank contains P pounds of water at 140 F on an average day and (140-78)P
>x 219/3 = 73 ft^2 tank, eg a 3'-tall x 9.6'-diameter folded cylindrical
>polyethylene film liner inside insulation inside a $200 3'-tall x 15'-
>diameter inflatable EZ-set swimming pool.
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.
Nick