
re: deployable doubt dispellers
26 feb 2006
m ransley wrote:
>... you say "with enough insulation you dont even need the sun"
you might understand that if you learned "ohm's law for heatflow."
>ok so what heats the house.
you and your internal electrical usage.
>and what is "enough insulation"
e = ir, in electrical terms. enough to increase the product of
the internal gain and the house thermal resistance to 30 f or so.
>i have higher than optimal insulation. r 100 attic, r 30 walls, r 7
>under basement concrete, and r 45.5 loweargon glass. cooking and people
>dont make enough to keep 1800 sq warm.
that's 1800ft^2/r100 = 1.8 btu/hf for the ceiling plus about 144ft^2/r4
= 36 for windows plus 2736ft^2/r30 = 91.2 for walls plus about 30 for 30
cfm of air leakage (if you caulk the house tight), ie a total of 159, so
you can keep it 70 f on a 30 f day if 70 = 30+q/159, where q = 6360 btu/h,
eg 1.86 kw, ie 45 kwh/day or 1342 kwh/mo. kinda high. upping the walls to
r60 would reduce g to 113 and the electrical usage to 957 kwh/mo. a new
house with more zoning or less heated space (eg closets on exterior walls)
might have g = 90, with 760 kwh/mo. replacing the windows with r60 walls
would make g = 56, with 473 kwh/mo. an airair heat exchanger could help.
nick

