Miller Farm:Degree Days
From Copelco
Contents |
Definition
A degree day is a measure that guages the amount of heating or cooling needed for a building. [1] Usually for an average outdoor temperature of 65° Fahrenheit, most buildings require heat to maintain a 70° temperature inside. Similarly, for an average outdoor temperature of 65° or more, most buildings require air-conditioning to maintain a 70° temperature inside. [2] Degree days are used as a guidepost to estimate heating and cooling requirements:
- Heating degree days (HDD) is a measure that tells us how many days each year, on average, the outside temperature falls below 65° F. [3] The higher the heating degree days, the cooler the climate.
- Cooling degree days (CDD) is a measure of how many days each year, on average, outside temperature exceeds 65° F. [3] The higher the cooling degree days, the hotter the climate.
Electrical, natural gas, power, heating, and air conditioning industries utilize heating and cooling degree information to calculate their needs. [1]
Derivation
The number of degree days (applied to any day of the week) is determined by calculating the mean temperature for the day and then comparing the mean temperature to a base value (usually 65° F). The mean temperature is calculated by adding together the high and low for the day and dividing the result by 2.
So, take the high and low temperature for the day, and average them. If this number is greater than 65 F, then we have (Average temperature - 65) cooling degree days. If the average temperature is less than 65 degrees, then we have (65 - Average temperature) heating degree days. Running totals are kept for these units over a time period of a year so fuel distributors and power companies can assess average demands. [2]
Examples
- If the outside temperature is 64 F for one full day, it is considered a 1 heating degree day.
- If the outside temperature is 60 F for a day, it is considered to be a 4 heating degree day.
- If the outside temperature averages 0 F for two weeks, the result is 910 degree days.
- 65 degree days * 14 days = 910 heating degree days
Maps and Graphs
 Annual Heating Degree Days |
 Annual Cooling Degree Days |
 Dennis Weather Station: Daily Minimum and Maximum Temperature Values |
External Links
References
- ↑ 1.1 1.2 National Weather Service Glossary
- ↑ 2.1 2.2 Degree Days FAQ : Weather Underground
- ↑ 3.1 3.2 Chiras, Daniel. The Solar House Passive Heating and Cooling. White River Junction, VE: Chelsea Green Publishing Company, 2002.
