another strawbale doghouse SOLAR.KnowledgePublications.com

another strawbale doghouse
21 mar 1999
my neighbor ray sells oldish 4x4x8' strawbales for $25 each, delivered and
stacked. we might arrange 8 of them into a 12' id x 20' od flat square, on
top of some black plastic film on the ground, with another 4 on top, and 4
4x8' insulating perimeter panels between them made from 2x4s on 2x8 centers
with r7.5 1.5" styrofoam board on each side of r13 fiberglass insulation,
with latex paint on the outside foamboard. 

two of the panels might be hinged at the bottom to open for ventilation,
using jade mountain's (800) 442-1972 $54 passive #fc115 thermofor vent
openers making a 15" gap at the top when the room temp reaches 70 f. the
other two might be fixed. the dogs might sleep on the 32' long x 3.5' wide
strawbale shelving 4' above the cool air near the ground at night. the
doghouse floor might be playground mulch over some old carpeting over
black plastic film on the ground. 

we might have a standard $200 20x20' commercial semicylindrical plastic
film greenhouse as the roof 8' above the floor, with a 2x4 on each side
of the 6 curved galvanized pipe bows and a 2x6 or a 6" strip of plywood
under that to sandwich up a floor made with 4' welded wire fencing with
a 2"x4" mesh ($40 for a 4' x 100' roll), with a 6" sag down the middle
of each 4' x 20' length to make it stronger. that might hold up a person
inside the greenhouse, with careful walking. the greenhouse peak would
be about 10' above its floor and 18' above the ground.

the ceiling insulation might be bags of leaves over a flat layer of clear
poly film to reduce condensation inside the greenhouse film, with a few
areas with no leaf bags to make skylights near the north wall. the curved
north wall of the greenhouse poly might be painted white to reflect more
sun down into the skylights. 

more interestingly, the ceiling might have a 16x16' poly film bladder
lying on the floor, two layers of film, sealed in a 1x3 sandwich around
the edges. this might be filled to a 2' depth (~r48) with tiny bubbles
at night in the winter (and during the day in the summer) with a shop vac
pushing air through a 2" pvc pipe that lies in a soapy solution along
the south wall. the bladder might be tilted 6" up to the north, so the
soapy solution collects on the south, and it might have a photocontrol
to sense when the foam has reached the north edge and shut off the vac,
which might draw air from a hose attached to the north edge, with an
adjustable hole in the vacuum hose to slightly pressurize the bladder. 

we might have some 110 pound dogs inside with an average heat gain of
2.5x6.6x110^0.75 = 560 btu/h per dog, according to wood et al on page
9.12 of the 1993 ashrae hof.

how many ashrae-standard dogs do we need to heat this house? 

say it's 15 f outdoors and we want 60 indoors, worst-case.

a 1'x2' dog door has a thermal conductance of about 2 btu/h-f, and
the strawbales have a thermal resistance of about 3 per inch, ie r144
for a 48" wall thickness :-) they have 512 ft^2 of outside surface and
256 ft^2 of inside surface for a log mean surface of 362 ft^2, so they
add 362/144 = 2.5 btu/h-f to the structure's thermal conductance. the
4 foamboard panels add about 128 ft^2/r28 = 4.6. the ceiling adds about
144ft^2/r48 = 3. we might have a couple of 2x4' r2 windows for another
8 btu/h-f. let's say there's no air infiltration. then the total indoor-
outdoor doghouse conductance is 20.1 btu/h-f, so we need 60 = 15+p/20.1
on a 15 f day, ie dogpower p = 900 btu/h, so a couple of 110 pound dogs
should do it... 

nick