Curbie said:
I was wondering if anyone has problems with this ways of calculation
house-hold heat loss?
Well, since you failed to specify a way, I have no problem with it.
It is engineering. It's not rocket science. If you can run a
spreadsheet, you can calculate it as finely as you care to account for
all the parts of your house. If not, you can't. If you assume your house
is built better than it is actually built, it will not give an accurate
indication of actual energy use, but that's a matter of the accuracy of
your model, not the standard equations of heat flow.
Useful approximations - 13.9 cubic feet per pound of air, specific heat
of air 0.24, 3413 btu/KWh, 91,500 btu/gallon propane, 138,000 btu/gallon
fuel oil. U-value = 1/R-value. Area (square feet) times u-value = heat
flow per degree F differential. Grab some climactic data and you can
compute yearly use at least two different ways (by degree-days and by
average temperatures) as well as size your heating appliances for
worst-case low temperatures and desired indoor temperature. Compare that
to what you actually use for a year and you can figure out if your model
is accurate.
Or, if you are not all that detail oriented, you can go to someplace
like
http://hes.lbl.gov/consumer/quick-general
and get a general idea based on reality-based assumptions.
With any method, garbage in == garbage out applies.
