|
|
re: passive solar; reduce the consumption of non-renewable resources
21 nov 1996
snark@swcp.com wrote:
>>...a house can be up to 30 degrees off truth south...
>assuming rectangular [in horizontal cross-section] houses, the ones
>that are between 30 and 45 degrees off true south could not be so oriented.
that's ok. the amount of sun decreases as a cosine function with azimuth,
so that makes 70% of the sun at 45 degrees, and lower sun elevation helps
se and sw walls get almost as much sun as south walls in the winter.
>...many streets (and the attendant houses) are oriented n-s/e-w.
another option is to add-on a greenhouse-type sunspace to the east or west,
or on a flat roof, in a city. people build plastic film greenhouses all the
time, 15,000 acres of them in the us, the largest ones covering more than
5 acres. the plastic needs to be tensioned somehow, to keep it from flapping
in the wind. the usual us solution is to use 2 layers and inflate them with
a small blower. mediterranean arched poly film greenhouses have straps on
the outside of 1 layer of film, between the curved bows, to keep it taut.
a standard commercial plastic film greenhouse built with curved galvanized
pipes allows growing food, etc. one might put a solar heat store for the house
in it, as well as some chairs, picnic tables, bare solar water heating panels
or pvs. these materials for these greenhouses cost about 50 cents per square
foot of floor area. the labor standard for putting up a 30' wide x 100' long
greenhouse in a field, from scratch, is 3 people, 1 day. expanded shale or
lava over poly film makes an interesting low-thermal-conductance floor with
a vapor barrier. a few plants might be ok as well.
if one has more time than money, the curved bows (~5 m tall in the middle x
~16 m long), can be made of 2 pieces of bent wood, 1x3s, each about 2 cm thick
by 6 cm wide, with spacers between, and some galvanized screws, reducing the
price of a 32' wide x 16' tall x 64' long (~10 x 5 x 20m) greenhouse to
foundation: 192' of pressure-treated 2x4s $100 (on edge, with 5/8" holes)
50 3' pieces of 1/2" iron rod 50 (ground spikes for 2x4s)
curved beams: 17 beams, each 50' long 1x3s 170 (32' horizontal span)
414 3" 1x3 spacers 10 (every 2')
828 galvanized screws 5
1x3 horizontal purlins and ridgepole, 192' 20 (3 of them)
1x3 cedar cap strips for film perimeter, 342' 100 (ripped 1x6s)
uv greenhouse polyethylene film: 64' x 50' 160 (this recyclable film
endwall film: 16'x 32' x 2 50 has a 3 year guarantee,
1/8" nylon twine for tensioning film, 800' 10 and lasts much longer
miscellaneous 50 with shadecloth over it
----- in the summer.)
total $725.
estimated labor 80 hours
cost/ft^2: 725/2048 $0.35
cost/m^2: $3.81
this sunspace would collect about 64x16x1000 = 1 million btu of heat on an
average january day in philadelphia, the heat equivalent of about 8 gallons
of oil. with an r0.8 single layer of poly film, and some sort of lengthwise
divider down the middle, it would lose about 6hr(68f-30f)1024/r0.8 = 300k
btu/day, for a net gain of about 5 gallons of oil per day. adding a shallow
skating rink to the south would increase the solar input by 30%, keep weeds
and lawnmowers away from the glazing and bring the net gain back to 8 gallons
of oil per day.
a 24' long x 16' wide x 12' tall (8x3x4m) strawbale box inside the sunspace,
containing 384 55 gallon sealed drums full of water, each drum storing about
25 k btu of useful heat as it cools from 130 f to 80 f, would store a total
of 9.6 million btu or 2800 kwh. an old house with a thermal conductivity of
600 btu/hr-f needs about 24hr(68f-30f)600 = 550k btu of heat on an average
jan day in phila, the heat equivalent of about 4 gallons of oil. this box
could store solar heat for about 9.6m/550k = 17 cold days with no sun at all.
if twice as long (48'), it could store heat for 35 days with no sun at all.
or, we could just keep bombing iraq to lower our heating oil bills.
until the oil runs out.
nick
spotted hyenas are the sharks of the savanna, superpreditors and astounding
recyclers of garbage. they hunt in large giggling groups, running alongside
their prey and eating chunks of its flesh until it slows down through loss
of blood, or shock, or sheer hopelessness, and then the hyenas grab for the
stomach and pull the animal to a halt with its own entrails or let it stumble
into the loops and whorls of its own body. they eat the prey whole and cough
back, like owls, the indigestible parts, such as hair and hooves...
from personal history: hyena
by joanna greenfield,
in the new yorker, nov. 11, 1996
|
|
