I'm wondering how reliable the ground temperature data is in the EPW weather files on the EnergyPlus website.
For instance I was looking at Calgary, AB, Canada from EnergyPlus.net.
Ground temperatures are generated by the EnergyPlus Weather Converter program as far as I am aware; it does not originate with the rest of the data in those files (though it seems to be based on annual DB values).
Original file contents:
GROUND TEMPERATURES,3,.5,,,,-5.32,-0.71,4.61,8.57,14.09,15.26,13.38,8.88,3.00,-2.46,-6.33,-7.35,2,,,,-3.94,-1.30,2.37,5.40,10.36,12.27,11.91,9.37,5.31,1.02,-2.60,-4.38,4,,,,-1.75,-0.59,1.57,3.57,7.30,9.21,9.67,8.57,6.20,3.29,0.48,-1.33
Formatted more readably:
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0.5 m -5.3 -0.7 4.6 8.6 14.1 15.3 13.4 8.9 3.0 -2.5 -6.3 -7.4
2.0 m -3.9 -1.3 2.4 5.4 10.4 12.3 11.9 9.4 5.3 1.0 -2.6 -4.4
4.0 m -1.8 -0.6 1.6 3.6 7.3 9.2 9.7 8.6 6.2 3.3 0.5 -1.3
So in January at 4m depth (about 13 ft.) it is below freezing.
Now this is just anecdotal but there is some evidence that calls this 4m temperature into question. According to the City of Calgary:
Frost depth This is the depth to which the ground is frozen. In Calgary, frost depth usually reaches an average of seven feet every year. It takes several months to reach this depth and usually occurs in late February or early March.
Though they say "average" depth I'd actually expect in normal practice that a local frost depth guideline would rarely actually freeze.
Calgary's statement seems to be roughly consistent with other sources as well.
So not only does the 4m temperature seem to be far colder than would be expected by the frost depth statement, but also as the peak it occurs the wrong time of year, 1-2 months early.
What procedure is used to generate this data? Are there any references or documentation?
Thanks!
