## 5 Results
### Yearly Results  
In this section, the yearly thermal energy demand for each investigated building geometry is reported. In Figure 5, the building is identified by a letter and a number. The letter indicates the shape/geometry of the building, while the number indicates the construction type: buildings marked with the number 1 have external tuff walls, and buildings marked with the number 2 have external empty box walls (Table 1). Figure 5 shows that building B1 has a greater yearly thermal energy demand than other buildings of different shapes. This can be explained by the shape of building B1, a closed courtyard building (Figure 1) with much higher shaded areas compared to other buildings that are more exposed to solar radiation. Conversely, the buildings with the lowest thermal energy demand are A1, F1, and F2, which are block buildings and tower buildings, respectively. These buildings have a smaller number of apartments and, therefore, a lower thermal energy demand for space heating. This is due to the assumptions of the developed model, which considers one apartment per floor for these buildings. The proposed system involves the use of thermal insulation materials on the external walls and the replacement of the condensing boiler with one of 0.98 rated efficiency. As a result, the thermal energy demands and related primary energies for all buildings decrease, as shown in both graphs in Figure 5. The average primary energy savings (_PES_) achieved for all buildings range from 21% to 37% (Table 10). The proposed energy measures result in the lowest primary energy savings of 21% observed for the four-floor line buildings, D1 and D2. Conversely, the highest primary energy savings of about 37% are observed for the tower buildings, F1 and F2. The highest primary energy savings at about 37% observed for the tower buildings F1 and F2 are mostly due to geometrical features. Although these buildings have lower absolute thermal and primary energy demands in the reference system due to their smaller number of apartments and overall floor areas, their higher surface-to-volume (S/V) ratio  
Figure 4: Monthly thermal energy demand in both reference and proposed (right) system. means that a greater proportion of their heat loss occurs through the building envelope. As a result, the application of thermal insulation has a more significant relative impact on reducing their total energy consumption. The insulation effectively reduces heat losses through the extensive external surfaces, leading to higher percentage savings compared to other building typologies with lower S/V ratios. Therefore, despite lower absolute energy demands, the relative weight of the insulation on the total consumption is higher for buildings F1 and F2 due to their geometric characteristics. Once the primary energies were calculated, the CO2 emissions for each building geometry in both the reference and proposed systems were estimated. An emission factor of 0.20 kgCO2/kWhp was used for this calculation. Additionally, the cost of natural gas per unit area for each building geometry was evaluated, assuming a unit cost of Euro 0.70/Sm3. For all geometries, the average yearly avoided CO2 emissions were 3.85 kgCO2/m2 (Figure 6), and the average yearly cost saving was Euro 2/m2 (Figure 7). The economic evaluation of the adopted energy measures, including the use of thermal insulation materials and the replacement of boilers, is performed. The total capital cost of the energy measures considers the specific cost per m2 of the thermal insulation materials, the capital cost of the new boilers installed in the considered buildings, and the technical costs due to surveys, feasibility studies, preliminary, final, and executive designs, as well as works management. Specifically, for the thermal insulation energy measure, the technical costs amount to about 25% of the total cost, while for boiler replacement, the technical costs amount to about 25% of the total cost.