Degree day

A degree day is computed as the integral of a function of time that generally varies with temperature.

The function can be estimated or measured by one of the following methods, in each case by reference to a chosen base temperature: A zero degree-day in energy monitoring and targeting is when either heating or cooling consumption is at a minimum, which is useful with power utility companies in predicting seasonal low points in energy demand.

Since the escape or ingress of heat due to conduction is proportional to the difference between the indoor and outdoor temperature, the amount of energy needed to maintain the base temperature indoors for some period of time is roughly proportional to the number of degree days.

Growing degree days are based on 5 °C, given that typical plant growth stops below that temperature.

[1] In Canada, Growing Degree Days are used in order to predict when mosquitoes and blackflies emerge and vanish.