alt.energy.renewable

Calab wrote:
>"Davej" wrote in message
>>>
>>> > Has anyone ever figured out how these dome doghouses leak? Maybe
>>> > condensation? They are worthless.
>>>
>>> Condensation is not a leak.
>>
>> Well, all I know is I'm tired of finding damp, moldy straw inside.
>
>Put a wooden skid, or something else that will let moisture drain
>underneath, yet keep the bedding, etc up off the ground.

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,
eg 2.6"x2.6".

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.

Nick