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re: a strawbale doghouse
3 mar 1999
 wrote:
 
>don't mind nick, folks.  he played the scarecrow in his high school
>production of "wizard of oz" and hasn't been the same since.  

never actually done that, altho i did sing a larry-hooper type bass solo
("bells of the sea") in front of 2,400 people at our high school music
festival. the terrifying part was anna moffo sitting in the front row of
the audience, just visiting from la scala. she managed to contain herself.
 
strawbales are very good insulators, compared to doghouse materials,
and one of the advantages of a modest-sized strawbale doghouse is that
it could be mostly heated by the dogs themselves. ashrae-standard 50
pound dogs make 354.9 btu/h of heat, like 100 watt light bulbs. some
superinsulated scandinavian houses are reputed to be mostly heated by
their electrical consumption and people and animals inside.

it's important to have a door that seals well. i see some pretty good
dog doors at pet stores. heavy plastic flaps that are hinged at the top
and swing both ways, with a magnet at the bottom that helps them stay
in the closed position. i think some have furry weatherstripping all
around the perimeter.

we might make a simpler superinsulated doghouse with one of those
doors and some strawbale walls and a wooden platform on top with
more strawbales on top for ceiling insulation and a piece of heavy
black epdm rubber roofing material over that. the shallow roofpond
might be fun, with a ramp that goes up to the roof for the dog so
he can take a drink, or a tube that goes down into the doghouse
with a float valve and a bowl, maybe a toilet :-) and poly film
sides over the outside of the bales with the roof rubber overlapping
the film so it sheds water. and for the floor, some black plastic
on the ground with some wood or old carpeting over that...

how big could one of these doghouses be and still be dog-heated?
a 1'x2' door has a thermal conductance of about 2 btu/h-f, and r50 
strawbales have 0.02 btu/h-f per square foot. if we want to keep
the inside 70 f on a 30 f day (the average in january where i live)
we need a maximum thermal conductance u, where 70-30 = 354.9/u, so
u = 8.75 btu/h-f. so... the door has 2, which leaves 6.75 for the
walls. with s ft^2 of exterior surface, at most, 0.02s = 6.75, so
s = 338 ft^2. this might be an l foot cube with a total surface
5l^2 = 338 ft^2, not counting the floor. then l = 8.2 feet, which
makes this one of my favorite thermal structures, an 8' cube.

if it were less than 8' tall, it would be warmer, with the same dog
inside. this doesn't count air leakage, which makes it cooler in
winter (altho we really should be using the log mean of the inside
and outside areas with such thick walls, which would make it warmer),
and it needs some venting in summertime...

around here, i'd use plastic bags of leaves for insulation instead
of bales, if building the solar heated version. bales sell for about
$2 each, but pa has lots of trees and leaves, and pa law bans leaves
from landfills and discourages burning. the state works hard to
encourage composting, but lots of people rake up leaves in the fall
and put them out for a special trash collection, paying 75 cents
a bag to have them removed. in this case, the enclosing structure
might be a quonset-hut-shaped plastic film greenhouse, and the "room"
might be another quarter-cylindrical structure that fits inside the
north half of the greenhouse, with a 2' gap between the inner and
outer films that's filled with bags of leaves.

nick




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