## 3 Case Study
### Initial Heating Needs  
To assess the heating needs of the building in the initial situation, an energy simulation of the building was carried out with the official tool in Spain for the energy certification of buildings. It is the LIDER-CALENER Unified Tool (HULC), which performs a detailed calculation in transitory regime of the building's thermal behavior on an hourly basis [36].  
For the simulation of the building using this software tool, the required information can be grouped into its geometry, thermal characteristics of the envelope and interior partitions, operational conditions, and external excitations (climate and surroundings elements casting shadows). The building is calculated with the geometric detail shown in Figure 4.  
In Figure 5, the energy demand for each dwelling in the winter period is shown. These values are ordered from higher to lower demand. It can be seen that the difference between the apartment with the highest demand and the one with the lowest is almost double, which could be equivalent to one apartment being in a much colder climate than the other.  
Figure 4: 3D-view of the building model using HULC software tool.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Opaque Elements** & **Windows** & **Total Area** & **Windows to** \\  & **U** & **U** & & & **Wall Ratio** \\  & **(W/(m\({}^{2}\)K))** & **(W/(m\({}^{2}\)K))** & **g-Factor** & **(m\({}^{2}\))** & \\ \hline North & & & & 449 & 0.23 \\ East & 2.97 & 5.7 & 0.8 & 324 & 0.09 \\ South & & & & 436 & 0.34 \\ West & & & & 270 & 0.11 \\ Roof & 1.41 & & & 328 & \\ Slab on ground & 1.49 & & & 215 & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Original building envelope characteristics.  
Figure 6 shows the flats with a heating demand higher than the mean in red. As expected, the ground-floor flats are, in general, those with the highest heating demand, as well as those on the north face of the building, with values above the average.  
To answer the question about differences in heating needs, the possible causes are discussed below. Thus, firstly, the north-facing dwellings all have a demand for high heating, due to two reasons: one is the orientation itself, which makes the solar gains in winter less, and the second is that these houses are the ones that present a greater area to the outside for the same volume, that is, a lower compactness. Secondly, there is also an above-average need for heating in dwellings in contact with the ground as they have heat losses towards it, something that does not occur on upper floors. Finally, on the first floor there are dwellings that on their lower face are in contact with the outside air. This fact makes the heat losses through the floor of these dwellings another reason for heating needs that exceed average.  
Figure 5: Heating space demand for each apartment (kWh/m\({}^{2}\).year). Ordered list from the worst to the best (“P” refers to the floor and “E” refers to the dwelling).  
Figure 6: Heating space demand for each apartment: Drawing view.  
In view of the previous results, where the differences in the demand for heating can be equivalent to a change of location, and as it is evident that in different locations, the insulation measures and, in general, the renovation measures of a building are different, it seems logical that in a case like this one, the insulation measures should be applied according to the needs of each apartment. Therefore, the ideal way is to propose different solutions for each facade of each flat. As this degree of detail may be impractical, the proposed solutions should probably be made for a group of facades and windows.