Cooling degree-day

Cooling degree-day (CDD) is calculated by summing the number of degrees below an average hourly outdoor “thresh-old” temperature, for a 1-day (24-h) period. A threshold temperature for cooling of 18.3 °C represents an ASHRAE(2001) standard numerical value, and is the commonly used value (ASHRAE 2005; NOAA 2013; Watts and Kalkstein 2004), although ASHRAE (2005) also use a threshold of 10 °C . Annual CDDs represent the sum of the degree-days throughout one calendar year. CDD also accounts for ambient temperature fluctuations associated with a temperature drop after a cold frontal passage or subsequent to a thunderstorm, bringing relief from heat stress (Watts and Kalkstein 2004).

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