What is the effect of windchill on design temperature?
AlanB4
| Posted in Energy Efficiency and Durability on
I recently got the Hot2000 data from the energy audit for my house, and i noticed the heating peak load is designed for -20C (-2.5F). Two days ago the temperature was -8C with a -21C windchill (below peak heating load).
Do the peak loads account for windchill or is the peak load the lowest expected temperature with any windchill?
I have a 40k furnace and it seemed to hit high fire but ran maybe 30-40 mins total out of each hour.
Thanks
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Replies
Alan,
The term "windchill" was developed to estimate the effect of wind on people. When a TV announcer says that the outdoor temperature is -8°, but the windchill temperature is -21°, the outdoor air temperature is (obviously) just -8°.
Design heating loads are calculated based on the outdoor air temperature. A good heat loss program might take wind into account by requiring an input that asks whether a house is in an "exposed location," an "average location," or a "sheltered location." These inputs address the fact that high wind speeds can increase the rate of heat loss through your home's thermal envelope. But you don't have to add any more fudge factors on top of the calculations made by your heating load calculation program.
When it is -8° outdoors, your house (and your furnace or boiler) thinks it is -8°. Don't worry about nearing your design heating load until the thermometer drops to -20°. Even if the thermometer hits -22°, your house is likely to stay warm.
Thanks for the answer, i actually replaced the furnace with a high efficiency (used to be 75k in and 60k out, 80% eff) with a 40k (38.2k out) and insulated the walls with cellulose, the current calculated heat load is 44k, so i'm being a bit risky this winter, but this year i hope to insulate the attic, and reduce the 14.86ACH50 by air sealing the crawlspace.
I remember reading about how high winds will "strip" away the heat loss of a home at a faster rate vs. sheltered/low-wind area. What winds will also do is exacerbate the air leaks within a home.
Homes are usually listed as Exposure A, B, C and D - Exposures C and D are more susceptible to high winds and racking. I still question the air tightness of homes built in high wind areas that experience a lot of racking. One thing with wood is that it is ductile and always moving. I would like to see the blower door test on a tight home a decade later. I would be confident that the home is no longer as air tight as it was the day it had the blower door test.