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re: sizing a heating system
10 jun 2000
news  wrote:

>how is a heating system size[d?] for a passive solar house?

some people define a "solar house" as "one with no other form of heat."

conservation of energy is a basic requirement. the amount of internal
heat gain (from people and their electrical usage) plus the amount of
solar energy that enters the house needs to meet or exceed the heat loss
from the house, measured over some definite time. energy in = energy out.

>how is the i[n?]solation calculated against the u value loss of sizing
>a conventional heating system. 

the average amount of solar energy that enters the house plus the average
internal heat gain needs to meet or exceed the average heat loss from the
house, ie the indoor-outdoor temperature difference (c) times the overall
metric u-value (ie the total thermal conductance of the house) in w/c. 

for instance, an airtight 2 meter cube with metric r4 walls has a total
u-value of 6x2mx2m/r4 = 6 w/c. keeping it 20 c inside on a 5 c day requires
(20c-5c)6w/c = 90 watts, ie 2160 wh/day. this might come from 2 100 watt
people living inside for 10.8 hours per day. 


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