Posted by Abby Normal on November 28, 2006, 1:55 am
Nick Pine wrote:
Lol nick is just saying that he is allowing for 600 kwh per month of
internal gain from electricial power or 'solar gain through windows'
He never allows for how the sun beats on the walls or the roof as usual
and treats any conduction through the walls/roof as if it was a simple
heat loss calculation, like always
Posted by nicksanspam on November 28, 2006, 4:59 pm
Sure. One hopes the 800 ft^2 roof of this 2-story addition will be
a light color. If so, it might reflect 80% of full sun and absorb
50 Btu/h-ft^2. With Rochester's average V = 8.2 mph July wind, we'd
have an airfilm conductance of about 2+V/2 = 6.1 Btu/h-F-ft^2, ie
something like this, viewed in a fixed font:
--- | R48
|----|-->|----*----www--- 70 F
For an extra 800x8.2/R48 = 137 Btu/h, or less, counting the R8 foil layer
under the ceiling.
Then again, as daestrom says, if the internal heat gains all come in
a short time, say 4 hours, it would help to include the thermal mass of
the attached house, with some open doors to make a thermosyphoning airpath
from the cathedral ceiling of the addition through the 2nd floor of the house
and back down to the first floor and back into the addition, in July.
Posted by Abby Normal on November 28, 2006, 7:06 pm
Well Nick, I have actually built something with thermal mass, a
reflective roof, and insulation exterior to the attic. To eliminate the
solar collection scheme, but I do not have to be concerned with ice
So you are insulating on the roof pitch or the ceiling plane. Majority
of heat transfer in an attic is radiant. Have you been in an attic with
R40 at the ceiling plane and superheated air above it?
The sun also elevates the temperatures of walls well above the ambinet
air temperature. Maybe search CLTDs on the HOF