As the energy consumption of a building depends on the climate conditions and since these climate conditions vary for one certain geographic region over the years, the consumption data has to be corrected for the local climate. Otherwise, it would not be possible to compare the results of the calculation instrument for one building in the different reference years.
In order to include a weather correction factor the final energy that is used for space heating is multiplied by the weather correction factor [1]. After this step, the total climate corrected final energy consumption of the corresponding energy source is multiplied with the specific CED or KEV factor. The result is the associated primary energy consumption.
Thus, a weather correction factor larger than one that represents a relatively mild winter simulates an increase in the amount of energy consumption of the building. This is necessary as the building would have consumed more energy under average climate circumstances. As a result, the different energy consumption ratios are comparable over the years.
The local climate correction factor comes from the comparison between the average of the winter temperature for the reference year and the average for the winter period over a long period fixed by the country (for example 30 years in France, 20 years in Germany). It’s also possible to calculate this factor from the degree days (DD): average DD / reference year DD.
Two assumptions are made in case you have not entered the exact contribution of one energy source to space or heating purposes which means that data has been entered only in the total field:
 In case there are entries in the total field for electricity and at the same time for other energies or energy sources (gas, fuel oil, coal, district heating, wood) the whole amount of electricity is assumed to be used for other purposes other than space heating whereas the other energies or energy sources are assumed to be solely for space heating purposes.
 If there is no entry other than electricity, a percentage of 70% is assumed to be used for space heating. The rest is assumed to be used for all other purposes and this energy consumption is not taken into account for the weather correction.

Please note that the weather correction that is applied in the Display® calculation instrument does not take into account climatic differences between two different geographic zones.
However, to make buildings situated in different climatic zones comparable, it is necessary to apply a specific classification scheme to each corresponding climatic zone. In order to keep the classification scheme concise and not too complicated the Display® calculation instrument uses an identical classification scheme for all participating cities. By applying such a uniform classification scheme, the results show in which buildings huge improvements can still be made.
It is known that, if national classification schemes were used, buildings that were formerly well-classified could be graded harsher than with this uniform classification scheme. Therefore, the Display® classification scheme is a scheme where good ratings are rather hard to obtain.

Please note that thermal solar energy is always linked with water heating.