Term: Cooling Degree Days

Heating degree days and cooling degree days are climatological metrics used to express the magnitude of the heating or cooling load in a given location. These metrics are expressed in terms of a “base temperature” (e.g., “Cooling Degree Days Base 65 F”). Cooling degree days are calculated by taking the daily average temperature; if it is hotter than the “base temperature,” the difference is calculated. This difference is summed for the period (week, month, year) in question. Note that cooling season data are often presented in terms of “cooling degree hours” (due to diurnal temperature swings), which are not directly translatable to cooling degree days.

Source: Hygrothermal Regions