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re: comparing a super-house with super-windows vs. a sunspace house
7 nov 1996
i wrote:
>consider 2 houses on an average day in philadelphia in december, with an
>average outdoor temperature of 36 f and an average 1,000 btu/ft^2/day of sun
>that falls on a south wall: a super-house with 200 ft^2 of r5 super-windows
>in the r20 south wall, with a solar transmission of 60%, and a house with a
>32' wide x 16' tall x 12' deep lean-to r0.8 polyethylene film sunspace on the
>r20 south wall, with a solar transmission of 92%, covered with shadecloth
>in the summer, with just a few windows in the house wall proper, and a 16'
>x 48' x 2' deep shallow frozen pond, made from a single 20 x 50' piece of
>epdm rubber in front of the sunspace that augments the solar input by 30%:
>                        super-house         sunspace house
>solar gain              120k btu/day        612k btu/day
>thermal loss             43k btu/day        123k btu/day
>cloudy day loss          43k btu/day         20k btu/day
>net energy gain          89k btu/day        489k btu/day
>                         (26 kwh/day)       (143 kwh/day)
>cogen possibilities:
>      solar closet      no                  yes
>      water heating     no                  yes
>      pv                no                  yes...

a little more explanation:

the practice of heating a house with a low-thermal-mass isolated sunspace is
not new, altho adding a solar closet inside one may be. these are called
"solaria" in canada, as popularized by the brace research institute in
montreal. i'm building a 2-story version of a polyethylene film "solar room"
as pioneered by s. r. kenin and others in taos, nm, and described in william
shurcliff's book _new inventions in low-cost solar heating--100 daring schemes
tried and untried_. the materials for this will cost about $500, and i expect
it will take me about 2 weeks to build.

some ways to get an idea of what these curved plastic film sunspaces look like
are to visit a local greenhouse grower or greenhouse supplier or to get a
$5 catalog from stuppy at (800) 877-5025 or e. c. geiger at (800) 4geiger,
http:/, or x. s. smith in new jersey. the materials to build
one of these greenhouses can cost less than $1/ft^2.

i'm attaching curved galvanized pipe half-bows ($36 each) from a gothic-arch-
type greenhouse to the south side of my house this week. they come from
geiger's 30' wide "northerner" plastic film greenhouse, which is 13' 3" tall
in the middle, as normally set up. the straight end that is normally at the
peak of this greenhouse will be at the ground, with the curved end that is
normally at the ground at the top, in this case. the pipes are 20' long
corner to corner and about 22' long along the curve, and 1.66" in diameter,
and get attached to the fascia board of the house with 2 small pieces of
angle iron and 3 bolts to make a hinge, in x s smith's lean-to detail. the
overall pipe length can be adjusted by slipping more or less of the straight
end of the pipe into a concentric ground post pipe, 50", 60" or 70" long, with
a 3/8" through bolt to hold it in place. the ground posts serve as foundation,
attached to a pressure-treated 2x10 on edge running along the ground.

these pipes will be set up on 4' centers, using 9 of them to cover the
32' x 16' south wall of my house, and the resulting sunspace will be about
12' wide at ground level, ie it will have about 12'x32' of floorspace,
covered with black plastic and pebbles, or maybe gravel and slate.

greenhouse polyethylene film comes in wide rolls, up to 40'x150' long, and
one standard roll size is 24' x 100' ($122 for 0.004" thick material) so
i'll adjust the pipe length to 24' along the curve, and use a single layer
of 24' wide poly with some nylon twine stretched over the outside between
the bows from top to bottom, following their curve, mediterranean-style,
to tension the film against wind fatigue. the film will have a large piece
of greenhouse shadecloth covering it in the summer, which should make it
last longer than the 3 year guarantee. rutgers prof david meer told me about
his greenhouse in the shade, covered with 6 year old poly film that is still
in good shape. greenhouse film is often recycled, vs discarded.

i'll be using some aluminum extrusion clamps ("uni-lock," geiger catalog
number 33-sl16, or stuppy's 10081/10082, at about $1/linear foot) to make the
film easy to change. a less expensive and more labor intensive alternative
is to make curved 1x3 spaced beams for about $5 each, and use cedar 1x3 cap
strips with deck screws to hold the film at the perimeter. 

the usual commercial practice in the us (which has about 15,000 acres of
poly film greenhouses) is to use 2 layers of film, and statically-inflate
them with a continuously running 50-100 watt blower to tension the film.


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