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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 dry-bulb temperatures) and a reference temperature. Degree-days 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 degree-day (HDD), and each degree above the base is one cooling degree-day (CDD). To calculate the number of heating degree-days 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 degree-days are a measure of the severity and duration of cold weather; the colder the weather over a given period the higher the cumulative heating degree-day value. Similarly, the warmer the weather over a given period, the higher the cumulative cooling degree-day value. The ability to compare one week, month, or other period with another using degree-days 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 energy-saving measures.

The growing degree-day (GDD), an extension of the degree-day 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.

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Measure of how cold or warm a location is over a period of time relative to a base temperature, typically 65 degrees F (although other base temperatures, such as 75 degrees F, can be used for cooling). To calculate the number of heating degree-days (HDDs) of a given day, average the maximum and minimum outdoor temperatures and subtract that from 65 degrees F. The annual number of HDDs is a measure of the severity of the climate and is used to determine expected fuel use for heating. Cooling degree-days (CDDs), which measure air-conditioning requirements, are calculated by subtracting the average outdoor temperature from an indoor base temperature.
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved


[di′grē ‚dā]
(mechanical engineering)
A measure of the departure of the mean daily temperature from a given standard; one degree-day is recorded for each degree of departure above (or below) the standard during a single day; used to estimate energy requirements for building heating and, to a lesser extent, for cooling.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


A unit used in estimating energy requirements for building heating and, to a lesser extent, for building cooling. It is applied to all fuels, district heating, and electric heating. Origin of the degree-day was based on studies of residential gas heating systems. These studies indicated that there existed a straight-line relation between gas used and the extent to which the daily mean outside temperature fell below 65°F (18°C).

The number of degree-days to be recorded on any given day is obtained by averaging the daily maximum and minimum out-side temperatures to obtain the daily mean temperature. The daily mean so obtained is subtracted from 65°F and tabulated. Monthly and seasonal totals of degree-days obtained in this way are available from local weather bureaus.

A frequent use of degree-days for a specific building is to determine before fuel storage tanks run dry when fuel oil deliveries should be made. Number of Btu which the heating plant must furnish to a building in a given period of time is where “Btu required” is the heat supplied by the heating system to maintain the desired inside temperature. “Heat rate of building” is the hourly building heat loss divided by the difference between inside and outside design temperatures. When the estimating procedure is applied to buildings with high levels of internal heat gains, as in a well-lighted office building, then degree-day data on other than a 65°F basis are required. See Air conditioning

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.


A unit used in estimating the fuel consumption for a building; equal to the number of degrees that the mean temperature, for a 24-hour day, is below the base temperature; the base temperature is taken as 65°F (18.3°C) in the US and as 60°F (15.6°C) in Great Britain.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
References in periodicals archive ?
The analysis is focused primarily on constructing a 13-year (1987-99) series of annual gridded thawing degree-day fields.
[N.sub.bin] = number of degree-day values in a [Z.sub.b] bin
Degree-Days, Heating (HDD): A measure of how cold a location is over a period of time relative to a base temperature, most commonly specified as 65 degrees Fahrenheit.
Heating, cooling, and other degree-days, calculated to various bases, are used extensively in a variety of fields of engineering and science.
The initial size of yolk-sac fry were significantly same, however, the total length and wet weight of the yolk-sac fry at 618 degree-days (swim-up stage/at the end of study) differed significantly among all treatments.
Such corrected time is commonly referred to as "thermal time", or "heat units", and basically it is the accumulated product of time and the difference between actual temperature (T) and Tb for each day (or hour), calculated in degree-days or degree-hours units (UC-IPM, 2014).
Where, Q was average daily discharge [m3/s], c was runoff coefficient expressing the losses as a ratio (runoff/precipitation), Cs referred to snowmelt and Cr to rain, a was degree-day factor [cm/C/d] indicating the snowmelt depth resulting from 1 degree-day, T was number of degree- days [C d] T was the adjustment by temperature lapse rate when extrapolating the temperature from the station to the average hypsometric elevation of the catchment or zone [C d], S was ratio of the snow covered area to the total area, P was precipitation contributing to runoff [cm].
To verify the savings in the energy use among the group of houses, two analyses were performed: a grouped analysis using a piecewise linear regression, or three-parameter change-point regression modeling, (Kissock et al., 2003; Baltazar et al., 2006) with uncertainty analysis, and a grouped analysis using the Princeton Scorekeeping Method (Fels, 1986), which is a type of variable based degree-day (VBDD) analysis.
where, [alpha] and [beta] are the base-level and the cooling (or heating) slope parameters; [H.sub.o] ([tau]) are the degree-days for the average weather data period at base temperature [tau] and [[epsilon].sub.I] is the random error term.
Annual degree-day information (including heating degree-day and cooling degree-day) is usually continuous.