Sounds like it needs a vapor barrier on the ground, eg plastic film under
Astroturf, and enough ventilation to keep the indoor air dew point below
the temperature of the indoor surfaces...
An ASHRAE-standard 50-pound dog makes 124.1 Btu/h of basal heat (vs 354.9
when normally active.) If 35% is latent, that's 0.043 pounds of water vapor
per hour, with 1 pint of condensation every 3 nights. In a 2'x4'x4' tall R8
doghouse with a 56ft^2/R8 = 7 Btu/h-F conductance and 5 cfm of fresh air,
he'd raise the indoor temp 124.1/(7+5) = 10.3 F, eg from 30 to 40.3 (brrr)
on a 30 F day. We could make 5 cfm flow through the 4'-tall 40.3 F doghouse
with a 5/(16.6sqrt(4'x(40.3-30)) = 0.047 ft^2 hole at the top, ie 6.75 in^2,
An outdoor humidity ratio wo = 0.0025 pounds of water per pound of dry air
(Phila in January), and 0.043 = 60m/hx5cfmx0.075lb/ft^3(wi-wo) make wi
= 0.0044 indoors, with vapor pressure Pi = 29.921/(1+0.62198/wi) = 0.211 "Hg
and dew point Td = 9621/(17.863-ln(Pa))-460 = 35.4 (a Clausius-Clapeyron
approximation.). With (40.3-30)/1ft^2/R8 = 1.3 Btu/h-ft^2 of heatflow and
an R2/3 indoor airfilm resistance, the wall temp would be 40.3-2/3x1.3
= 39.4 F indoors, with no condensation.
A fancier doghouse might have more insulation and passive solar heat and
a condensing double-wall thermal chimney (a passive thermosyphoning ERV)
and 2 strawbales to make a sleeping platform above the top of the entrance
door, so warm air is trapped upstairs.
On Feb 16, 3:31 am, email@example.com wrote:
Helpful calcs on the dog house -- thanks.
Where does the ASHRAE dog data come from? The fundamentals volume? or?
I've been working on a solar dog house -- some results to date:
Control Igloo House:
My control for the new doghouse is an igloo style, uninsulated dog
house with an improvised heavy cloth door. It has a 40 watt bulb
inside to simulate dog heat. It is worthless. The only time the
temperature in the igloo goes above ambient is for an hour or two a
day when the sun is shining directly on the door, otherwise it tracks
with a couple degrees of ambient even when the 40 watt dog is on. I
suppose it provides some wind protection, but thats about it.
New Solar Dog House Prototype Description:
The prototype solar dog house is wood construction.
Insulated to an average of about R12 on all sides, ceiling and floor
-- mostly 2 inch polyiso.
Floor is single layer brick for thermal mass (insulation below this).
Entrance is a tunnel arrangement with commercial heavy poly dog
flapper doors that seal fairly well -- one on each end of the tunnel.
First entrance is part way below 2nd for some, but not enough for full
Inside space is just large enough for dog to stand in, turn around,
and lay down to minimize heat loss. Roof is flat to minimize volume
and provide a place to dog to lay around on roof.
"South" wall is about 80% glazed (a high fraction of floor area). The
glazing is homemade double Acrylic that seals well. The house is on
ball casters so that the "south" window can be turned to the north in
the summer to prevent overheating.
I'm planning on adding solar chimney in summer.
As mentioned, the Igloo is near to worthless, and just tracks ambient.
The protoype solar behaves better, but well short of perfect.
On a sunny day, temp inside the dog house can go up to as high as 110F
even when ambient is 20F. Too much glazing for the mass. This day
overtemp may not be a serious problem in that dogs spend day mostly
At night, the prototype maintains about 15 to 20F over ambient. The
effect of the dog simulating 40 watt bulb can clearly be seen on the
temperature plots -- there is a distinct reduction in temperature drop
rate when the light goes on -- so insulation and sealing are good
enough to make a small heat source useful in heating the space.
I would call the current night performance marginal in a cold climate,
but much better than the Igloo.
Yesterday, I tried adding 10 gallons of water in black painted pails
to the house. Positioned so they got sun through the window. This
resulted in a big change for the good. Peak day temp was down to 90F
where it would have been easily been over 110F. Night time
temperature drop rate was less than half the previous rate. Morning
temp was nearly 30F over ambient and a comfortable 55F. I guess (not
surprisingly) that mass helps.
Brick floor is undesirable, but putting a pad over the brick means the
brick mass does not get direct sun. How to get good solar transfer to
the mass and still have a good sleeping surface?
How to add more thermal mass without taking up too much space?
Would I be better off with less (maybe much less) glazing, and just
rely on dog heat + good insulation + thermal mass to even out the
temperature and keep it enough above ambient for dog comfort? This
seems like it might have some benefit on strings of cold, cloudy days
I'd like to hear more about the "condensing double wall thermal
Not sure if when I add dog produced moisture if I can stand the
ventilation rate that will be required to control condensation?
Any ideas anyone has on making the design better?
On Feb 16, 1:44�pm, firstname.lastname@example.org wrote:
dogs should live indoors with their family. not outdoors espically in
too hot cold wet or snowey weather. we have 3 furry friends they have
dog doors, and a fenced in yard for their protection.
dogs forced to live outdoors, thats just plain cruel!!!!!!!!!
Chapter 9 (Environmental Control for Animals and Plants) of the ASHRAE
Handbook of Fundamentals says the basal heat of a W pound animal is
6.6W^0.75 Btu/h... 35% is latent, for a normally active dog.
Nice... Maybe R14, with foil.
Ohoh. Direct gain, aka "direct loss" :-)
You might make a U-shaped strawbale platform with the entrance door into
the opening of the U, inside an icosahedron made with 15 5.5' equilateral
triangles cut from 5 4'x8' sheets of foil foamboard with some foam in a can
for glue at the seams and white paint over it all. That would have
a 5.5/tan(36) = 7.6' inner diameter and a 4' stemwall height and a peak
0.526x5.5 = 2.9' above that. Pretty big.
You could make a smaller version with more cutting and piecing. Maybe
divide each large triangle into 4 smaller triangles, conceptually, and
divide the foamboard into thirds lengthwise to make 5 big triangles
and 1 3/4 triangle and 4 small triangles and 6 half-small triangles,
like this, cut from 2 4x8 sheets, viewed in a fixed font:
----------------------------- The big triangles would have 3.7'
|1/ \\ / \\ / \\2| edges, and the dome would have
|/ 1 \\ / \\ / 2 \\| a 5.05' ID and a 2.7' stemwall
|-----\\ 1 / 2 \\ 3 /-----| height and a peak 1.9' above.
|\\ 3 / \\ / \\ / \\ 4 /|
|3\\ / \\ / \\ / \\ /4|
|--/ \\-----------/ \\--|
|5/ 4 \\ 1 / 5 \\6|
|/ \\ / \\|
Sounds nice, on a sunny day.
An overhang might be more practical.
How about some mostly-shiny mass under the ceiling, with a insulated wall
between the glazing and the living space to make a sunspace and a vertical
duct on the living space side of the wall to allow hot ceiling air to return
to the sunspace without overheating the room? Maybe the dog can learn to
move around in the living space to stir up the air and bring down warm air
from the hot mass as needed. Alternatively, he might partially crawl under
a radiation shield to avoid overheating from the mass.
The dog could have a small well-insulated sleeping enclosure inside
the living space, a bedchamber, as in Jefferson's Monticello.
The dog might need 5 cfm of fresh air for breathing, which is enough to
avoid condensation on indoor wall surfaces, but the living space will be
warmer if outgoing indoor air heats incoming outdoor air on the way out.
More insulation will raise the indoor surface temp and allow higher
indoor humidity with less ventilation... 5 cfm adds about 5 Btu/h-F
to the doghouse conductance to outdoor air, or less, with the condensing
chimney, which acts like a normal air-air heat exchanger until outgoing
air begins to condense as it travels upwards. Above that point, the heat
transfer rate roughly doubles, with condensation happening on one side
of the common wall, and the outgoing air temp drops less than it would
without condensation, for the same heat energy removal.
Oops. The big triangles would be 3/cos(30) = 3.46' on a side, and the dome
would have a 4.77' ID and a 3' stemwall and a peak 1.82' above that, with
64 ft^2 of surface, vs 80 ft^2 for a 4' cube, not counting the floor.
A 4' R12 cube with G = 6x4'x4'/R12 = 8 Btu/h-F and a 40 watt bulb and
no air leaks might be 40x3.412/8 = 17.1 F warmer than the outdoors...
5 cfm of fresh air would make it roughly 40x3.412/13 = 10.5 F warmer.
With indirect gain, if 1020 Btu/ft^2 falls on a south wall on an average
22.8 January day with a 31.8 max in Billings, a 4' R12 cube with 16 ft^2
of R2 sunspace glazing with 80% solar transmission over an air gap over
an R12 insulated south wall with lots of shiny ceiling mass and surface
and a 65 F average living space temp would have 0.8x16x1020+40x3.412x24h
= 16332 Btu = 6h(T-27.3)16/2 [for the south wall during the day]
+18h(65-22.8)16/18 [for the south wall at night] +24h(T-22.8)16/12 [for
the ceiling] +24h(65-22.8)4x16/12 [for the other 3 walls and the floor]
Btu/day, with ceiling mass temp T = 154 F, if I did that right.
If the average ceiling mass temp is (154+65)/2 = 109.5 over 5 cloudy days
while the cube loses 5x24((65-22.8)5x16/12+(109.5-22.8)16/12-40x3.412)
= 31254 Btu = (154-65)C, ceiling mass C = 351 Btu/F, eg a 4.2" x 16 ft^2
layer of water. Another layer of R12 ceiling insulation would help.
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