Passage III

Heating degree-days (HDD) and cooling degree-days (CDD) are used to estimate the amount of energy needed to heat or cool, respectively, any building on a given day. HDD are calculated by subtracting the daily mean temperature (T_d) from a base temperature of 65°F. Each degree difference is one HDD. CDD are calculated by subtracting 65°F from T_d.

Table 1 lists, for each of 10 US cities, the latitude of the city and the city's total HDD and CDD for a 1 yr period.

For the state of Illinois, the annual total HDD and the annual total CDD were determined for each of the years 1985-2010 (see Figure 1).