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re: heat cost
20 apr 1998
lowells460 wrote:
>does anyone have a simple formula?
sure. add up each exterior surface divided by its r-value, and the
volume divided by 60 (or 30, if it's an old house, or 240, if it's an
airtight house.) multiply this (thermal conductance) sum by 24 (hours)
and the number of heating degree days and the fuel cost.
for instance, a 16' cube with 6" of fiberglass (r20) insulation and
64 ft^2 of r2 double-pane windows has a thermal conductance of about
64 ft^2/r2 = 32 btu/h-f for the windows, 1344ft^2/r20 = 67 for walls,
and 4096 ft^3/60 = 68 (cfm) for air infiltration, a total of 167 btu/h-f,
so it takes 167 btu to keep the cube 1 f warmer inside than outside for
1 hour (or 160k btu for 24 hours, when it's 70 f inside and 30 f outside.)
dayton, ohio, has a 5708 heating degree day winter, so heating the cube
there takes 24hx5708x167 = 23 million btu, which might come from 230 $1
gallons of oil burned at 70% efficiency, a 1500 watt gasoline-powered
honda generator running 5 hours per day, some clear south siding and a
few dozen water-filled oil drums, or 2.2 ashrae-standard jersey cows
on the ground floor (caution: do not use holsteins.)
nick
nicholson l. pine system design and consulting
pine associates, ltd. (610) 489-0545
821 collegeville road fax: (610) 489-7057
collegeville, pa 19426 email: nick@ece.vill.eedeeyou
computer simulation and modeling. high performance, low cost, solar heating and
cogeneration system design. bsee, msee. senior member, ieee. registered us
patent agent. hi/dvc board member. web site: http://www.ece.vill.edu/~nick
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