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re: mobile homes inside commercial plastic film greenhouses
25 jun 1996
gunslinger  wrote:

>nick@vu-vlsi.ee.vill.edu (nick pine) wrote:
 
>yo, nick! 

greetings, gunslinger...

>10 x 30 x 7 is more like a _camper_ than a mobile home (from one who
>currently lives in a 14 x 70 x about 12 mobile home.)

i used to know a couple who lived in a pickup truck... you have more space
than most sailors... i wonder why yours is 12' tall, 8'+ wheels? and how
do you haul that 14' wide thing on the road? someone was telling me that
there are more mobile homes sold in this country than houses, these days.
i'd like to find a manufacturer who is interested in solar heating them.

>seems to me it would get too hot to do much in the way of work, except
>in the dead of winter.

putting some shadecloth over the south wall, rolling up the plastic film at
the edges, opening endwall doors and having a vent or two at the top might
take care of that, leaving this house in the shade cooler than most houses
sitting in sun. one might also cover the flat roof with a single layer of
epdm rubber, with a 2" board under the edge, to make a shallow pond to keep
the roof at the wet-bulb temp. and divide the solar closet underneath into
two sections, one to stay hot for hot water, and one to stay cool by night
ventilation. the cool part might have another shallow epdm rubber pond
underneath, and one might pump some of the cool water up into the house
through a fan coil unit.

let's see. you have 2(14+70)x8' of r11 walls, and 200 ft^2 of r2 windows?
for an overall thermal conductance of 220 btu/hr-f, which might gain
8 hr(95.5-75)222 = 36k btu/day at 75 f inside in august in austin tx, where
the average daytime high is 95.5 f and the average wet bulb temp is 69 f.
this might raise the temp of 60 drums full of water from 69 f to 69 f +
36k/30k btu/f = 70.2 f every day, before the water cools down again at night.

the $139 all-copper 2' x 2' shw 2347 duct heat exchanger made by magicaire
might make a nice fan coil unit, if attached to the suction side of a $20
box fan. it moves 45k btu/hour between 125 f water and 68 f air at 1400 cfm,
with a 0.1" h20 air pressure drop, so it might move 4k btu/hr with a 5 f
delta t, ie 70 f water and 75 f air. you'd want a tiny submersible pump to
move about 4000/5/8/60 = 1.6 gpm through a head of about 4'. hmmm. that's 
about 1 ft lb/sec, and 1 hp is 550 ft-lb/sec, or 746 watts, so a perfect
pump might use 1.2 watts for that job. putting the duct heat exchanger up
near the ceiling would be a good idea, with a thermostat to turn on the fan,
and a gutter and drain under the heat exchanger. 

you might control humidity with a solar-dried dessicant system, eg a nice
triethylene glycol (which absorbs 11x its weight in water) or lithium chloride
pond on the roof, or a thin reinforced concrete floor with some insulation
underneath in the greenhouse, or some sort of vermiculite, charcoal, zeolite,
clay or calcium chloride sandbox, or even a pile of sheepskins somewhere
inside the greenhouse (a wool rug will absorb 23% of its weight in water from
moist air, according to the ashrae hof), all exposed to the sun and vented
outside during the day, and washed with house air at night.  

>=>putting the solar closet under the mobile home means we get some
>=>heat through the floor, which would otherwise be wasted if the closet were
>=>adjacent, and if we open a motorized damper under a floor return, we might
>=>easily get warm air to flow up into the mobile home by natural convection. 
 
>and you would lose the valuable storage space underneath the home,
>thus requiring the construction of some sort of outbuilding.

like a 30' wide x 100' long x 15' tall commercial plastic film greenhouse
to enclose your mobile home, costing $2k, requiring 1 day for 3 people to
set up, from scratch? :-)

>idea:
>what about setting the mobile home against a hillside, framing awnings
>over the outward facing windows and door(s), blowing shot-crete over
>the whole thing (for strength), and then covering it all with dirt,
>blending it in with the contour of the hillside. might be the world's
>first earth-sheltered mobile home.

i wouldn't call that very "mobile" :-) you might hump up the flat roof with
some soil first, to make it stronger. and put some sort of insulation over
the shotcrete, perhaps, and a layer of epdm rubber over that. putting some
large rocks on top of the soil might make for an interesting vaulted stone
ceiling inside your underground mobile home, if you removed the roof and soil
after the concrete set. you might want to consult an architect re aesthetics.

i like monolithic domes (800) 608-0001, which are made by inflating an
airform (like a tennis court cover), spraying the inside with 3" of urethane
foam, wiring up some rebar, and spraying the inside with 2" of shotcrete...
these can be wonderful passive solar structures, as well as fireproof,
tornadoproof, fast and cheap. they have been building these things up to 
260' hemispheres so far, for 20 years now, and they are working on plans for
1200' hemispheres. at last year's convention, someone asked whether he
could bury one under 60' of dirt. the answer was yes. oddly enough,
nobody asked why.

nick

it's a snap to save energy in this country. as soon as more people become
involved in the basic math of heat transfer and get a gut-level, as well as
intellectual, grasp on how a house works, solution after solution will appear.

					  tom smith 



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