Heating degree day

Encyclopedia : H : HE : HEA : Heating degree day

Heating degree day (HDD) and cooling degree day (CDD) are quantitative indices demonstrated to reflect demand for energy to heat or cool houses and businesses. These indices are derived from daily temperature observations.

Heating degree days are calculated over a period of time (typically a year) by adding up the differences between each day's mean daily temperature and the "balance point" temperature of 18 °C (or 65 °F), above which the building is assumed not to need any heating (the actual indoor temperature will be higher due to insulation retaining heat from the occupants). Thus three successive winter days with average temperatures of 4 °C, −2 °C and −4 °C totals to 56 HDD. Conversely, three summer days of 26 °C, 28 °C, and 30 °C totals to 30 CDD. For differences between day and night temperatures, the average is taken; so a day maximum of 10 °C with a night minimum of 2 °C averages to 6 °, or 12 HDD.

The system has several problems. Heat requirement is not linear with temperature (Valor et al., 2001), and heavily insulated buildings have a lower "balance point": some will need heating below 18 °C, but others won't need any heating until the temperature is much lower (see Superinsulation). Solar gain (see Passive solar) reduces the need for heating on sunny days (but not cloudy days), and wind increases it (by an amount that depends on how tightly the building is constructed). People also differ in their opinions about what constitutes a comfortable indoor temperature.

Note that in the United States, HDD figures appear much higher due to the use of the Fahrenheit system; to convert °F HDD, divide by 1.8 to get °C HDD, multiply by 1.8 for the reverse.

See also

• Weather derivatives
• Growing degree day

References

• Valor, E., Meneu, V., Caselles, V., 2001. Journal of Applied Meteorology 40 (8): 1413–1421 [Abstract]
• [Calculating heating degree days (North American conventions)]
• [Calculating degree days (British conventions)]
• [Weather derivatives]
• [Calculating required furnace sizes from HDD]

• [Year to Date Degree day comparison]

 

---

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.