[Greenbuilding] HDD and how they are calculated (daily avg. vs hourly avg)

[Peter Kidd]

in my little city, temperatures are routinely different, several C not 
uncommon, between downtown and airport, some houses are 4' apart in 
treed neighbourhoods, some are on bald acreages, and so on and so forth, 
gauge the accuracy of HDD accordingly

then there's baseline, what are you using HDD for and what is your 
reference temperature, what is the balance point you should reference, 
apples to apples of 18C may not be appropriate, if you look at natural 
gas demand at the utility, at when natural gas starts to flow for space 
heating en masse, a better reference temperature (for space heating 
appliances) is between 14 and 15C