Obviously, the consumption of energy used for heating is higher during cold winters than during mild winters. Elimination of the effects of cold and mild winters, helps to gain insight in temperature-independent energy consumption. The correction is made on the basis of the number of degree days in a particular month or year.
The number of degree days on a particular day is 18º centigrade minus the average temperature within twenty-four hours under the assumption that the heating is turned on when the outside temperature drops below 18º centigrade. All degree days per day are added up for each month.
- average daily temperature 20º Centigrade: no degree days
- average daily temperature 10 degrees centigrade: 18-10 = 8 degree day
- average daily temperature -4º centigrade: 18-(-4) = 22 degree days
In total over these three days 30 degree days.