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 and power demand. Power demand may be measured for a building, a power utility account, or consist of all the customers within a power utility's service area. In economics and finance an index (for example a price index, a stockmarket index) is a benchmark of activity, performance or any evolution in general. ... The supply and demand model describes how prices vary as a result of a balance between product availability at each price (supply) and the desires of those with purchasing power at each price (demand). ... For other uses, see Temperature (disambiguation). ...

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°C HDD for the three day period. Here's the calculation: (4°C + -2°C + -4°C)/3 = -0.667°C average HDD per day. 18°C(3days) - (-0.667(3days)) = 56°C HDD for the three day period. Conversely, three summer days of 26°C, 28°C, and 30°C totals to 30°C CDD for the three day period. 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°C. Now, plug that into the equation. From a balance point of 18°C subtract 6°C = 12°C HDD. Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ... For other uses, see Fahrenheit (disambiguation). ... Thermal insulation on the Huygens probe The term thermal insulation can refer to materials used to reduce the rate of heat transfer, or the methods and processes used to reduce heat transfer. ...

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. Superinsulation is an approach to building design, construction and retrofitting. ... Solar panels are used in passive and active solar hot water systems Passive solar technologies convert sunlight into usable heat, cause air-movement for ventilation or cooling, or store heat for future use, without the assistance of other energy sources. ... For other uses, see Wind (disambiguation). ...

Note that in the United States, HDD figures appear much higher due to the use of the Fahrenheit system. For other uses, see Fahrenheit (disambiguation). ...

To convert ºF HDD to ºC HDD: (5/9)x(Temperature in Fahrenheit) -32

To convert ºC HDD to ºF HDD: (9/5)x(Temperature in Celsius) + 32

See also

• Degree day
• Sol-air temperature
• Heating,ventilating, and air-conditioning
• Weather derivatives

A degree day is a measure of heating or cooling. ... Sol-air temperature (Tsol-air) is a variable used to calculate cooling load of a building and determine the total heat gain through exterior surfaces. ... HVAC may also stand for High-voltage alternating current HVAC systems use ventilation air ducts installed throughout a building that supply conditioned air to a room through rectangular or round outlet vents, called diffusers; and ducts that remove air from return-air grilles Fire-resistance rated mechanical shaft with HVAC... Weather derivatives are financial instruments that can be used by organisations or individuals as part of a risk management strategy to reduce risk associated with adverse or unexpected weather conditions. ...

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