What are Degree Days (Heating, Cooling, & Growing)?
Heating Degree Days Heating Degree Days (HDD) are used as an index to estimate the amount of energy required for heating during the cool season. When the daily mean temperature falls below 65 degrees Fahrenheit, most buildings require heat to maintain a comfortable interior temperature. By monitoring heating fuel usage and heating degree day accumulation over a period of time, a building’s energy consumption per HDD can be calculated and this value used, for example, in fuel consumption monitoring, energy efficiency evaluation or future fuel supply estimates. The daily mean temperature is found by adding together the high and low temperature for the day and dividing by two. When the mean temperature is above 65 F, the HDD total is zero. If the mean temperature is below 65 F, the HDD amount is the difference between 65 F and the mean temperature. For example, if the high temperature for the day was 68 F and the low 52 F, the mean temperature for the day would be 68 + 52 = 120 / 2 = 60 F
