Cooling Degree Days
A cooling degree day (CDD) is a measurement designed to track energy use. It is the number of degrees that a day's average temperature is above 18°C (65°F). Daily degree days are accumulated to obtain annual values.
Cooling degree days can describe the overall need for cooling. For example, the highest temperature in a day was 32°C and the lowest temperature was 19°C. Then, the mean temperature for that day was (32+19)/2 =25.5. The result is above 18°C, so the cooling degree days are 25.5-18 = 7.5°C.