degreedaydegreeday, a unit of measure used to estimate the fuel and power requirements in heating and cooling a building; it is equal to a difference of 1 degree between the outdoor daily average temperature (the mean of the maximum and minimum daily drybulb temperatures) and a reference temperature. Degreedays are an indicator of how far the average temperature departs from a human comfort level called the base. In the United States the base is generally 65°F (18°C), although in very warm or cold locations an alternative may be used, while in Great Britain the base is 15.5°C (60°F). Each degree of outside average temperature below the base is one heating degreeday (HDD), and each degree above the base is one cooling degreeday (CDD). To calculate the number of heating degreedays in a month, for example, the outdoor average temperature for each day is subtracted from the base, and the results for each day are added (with negative remainders being treated as 0). Heating degreedays are a measure of the severity and duration of cold weather; the colder the weather over a given period the higher the cumulative heating degreeday value. Similarly, the warmer the weather over a given period, the higher the cumulative cooling degreeday value. The ability to compare one week, month, or other period with another using degreedays permits the analysis of seasonal patterns of energy consumption, enables the setting and tracking fuel and power budgets, and can be used to verify that projected economies are achieved by energysaving measures. The growing degreeday (GDD), an extension of the degreeday concept, is defined as a day on which the mean daily temperature is one degree above the minimum temperature required for the growth of a particular crop. The GDD is used as a guide to planting times and for determining the approximate dates when a crop will be ready for harvesting. The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved. More on degreeday from Fact Monster:
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