🚀 go-pugleaf

A long, long time ago, on April 20, 1993, Thomas J. Downing asked the
following question (which I found while clearing out some useless old stuff
from my mailbox):

>       What exactly is a heating degree day and how is it computed?
>
>Thanks for your help!
>
>                                      Thomas J. Downing
>                                      TD7528@ALBNYVMS.BITNET

NOAA uses 65degF as the base for a heating degree day.  If the average
temperature is above 65degF on a given day, there are zero heating degree
days.  If the average temp is below 65degF, then the number of
HDD=(AvgT-65degF), e.g., there wd be 80 HDD on a day with AvgT=-15degF.
Usually, HDDs are used as monthly, seasonal, or yearly aggregates.

Cooling degree days are a corollary to heating degree days: the algorithm
is the same, but in reverse (i.e., CDDs accumulate on days when AvgT >
65degF)

You will often see references to freezing and thawing degree days, which
(obviously) use a base of 32degF or 0degC.

Daily average temperatures, by the way, are calculated simply by taking the
mean of the daily max and min temperatures.  This is not the ideal way to
do this, but this is simple.

I wd have answered this question sooner if I hadn't forgotten about it.




Tim Horrigan
US Army Cold Regions Research & Engineering Lab
72 Lyme Road
Hanover, NH  03755

ph: (603) 646-4432

internet: horrigan@hanover-crrel.army.mil