Bug in Tabula building area calcuation

Created by: marcusfuchs

By default the SingleFamilyHouse classes in teaser/logic/archetypebuildings/tabula/de/singlefamilyhouse.py and teaser/logic/archetypebuildings/tabula/dk/singlefamilyhouse.py contain 1 single zone. For a special use case, we want to add a second zone to this archetype. This exposed a bug in the area calculations performed in generate_archetype(). All areas are calculated similar to:

outer_wall.area = (
    self.facade_estimation_factors[self.building_age_group]["ow1"]
    * type_bldg_area
) / len(self._outer_wall_names_1)

For 1 zone, this leads to correct results. But for more than 1 zone the total outside area of the building is not distributed between the zones. Instead, each zone gets the full outside area assigned to it, so that 2 zones result in twice the outside area compared to a 1-zone model for the same building. This is because the equations use type_bldg_area when in fact they should use zone.area instead. The following leads to correct results:

outer_wall.area = (
    self.facade_estimation_factors[self.building_age_group]["ow1"]
    * zone.area
) / len(self._outer_wall_names_1)

As IMO this is a bug, I will branch of the master branch and submit a PR back to master.