## 3 Discussion on Results  
### Results on Global Costs of Measures and Primary Energy Consumption  
It should be emphasised that each school building is studied in the initial state at an energy demand level, L0, subsequently implementing sets of measures, as seen in Sections 2.1 and 2.1.2. As a result of relating 30-year global costs per m\({}^{2}\) to each set of measures and the consumption of primary energy per m\({}^{2}\) and year, the graphs obtained show an optimal intervention cost for each school building type (Figure 4a-c). Overall, it is noted that, in the three building types, for the same combination of measures, as in the WF thermal envelope elements, the energy demand levels (L1, L2 and L3) do not imply great differences in terms of global costs and resulting energy consumption. The graph clearly shows how different combinations of measures are grouped together according to construction elements enhanced. Moreover, when comparing the graphs of representative building types it is clear what set of measures or thermal envelope elements obtains optimal costs. For type A buildings, sets of measures introducing roof insulation obtain a greater reduction in energy consumption at the lowest global cost over 30 years. In this case, and depending on the energy demand level in terms of transmittance, consumption reduction regarding the initial state (L0) is between 24.5% and 25.3%, for interventions on the roof (R); between 28.1% and 30.2%, for improvements in facade and roof (FR); between 30.8% and 32.2%, for windows and roofs (WR); and between 34.8% and 38.1%, if the three thermal envelope elements (WFR) undergo improvements. The energy saving gained would enable to recover initial investment in such improvements within 4-5 years (R), 5-6 years (FR), 15 years (WR) and 14 years (WFR). The cost-optimal levels of interventions would be R and FR, thermal envelope elements, with a lower global cost. A greater saving is obtained through the OR and OFR, elements improved in the thermal envelope. For type B and C buildings respectively, the sets of measures with the lowest global cost over 30 years include facade thermal insulation (F), and facade and roof thermal insulation (FR). These sets of measures represent a decrease in consumption between 15.8-18.6% (F) and 16.6-19.2% (FR) for type B buildings, and between 18.6-21.1% (F) and 20.5-22.9% (FR) for type C buildings. The repayment term is less than 7 years in type B buildings, and between 12-13 years (R) and 19 years (FR) in type C buildings. Figure 4: Cost-optimal graphs. Correlation between 30-year global cost per m\({}^{2}\) in the sets of measures proposed and building’s primary energy consumption per m\({}^{2}\) and year, after the intervention, assuming a price increase rate of 1%. (**a**) Type A school building; (**b**) type B school building; (**c**) type C school building. In building types B and C, a greater reduction in energy consumption is obtained after replacing facades and windows (WF), as well as renovating all thermal envelope elements (WFR). In both sets of measures, the global costs increase, which means a longer repayment term for the investment made. In type B buildings, the global cost would be very similar to 30-year global cost, without necessary performance in the building. That is, the initial state L0, even exceeding it in some cases, which implies that the 30-year investment recovery is greater. Table 5 is drawn up in order to provide accurate figures and facilitate comparison with some results included in the previous graphs. It shows 30-year global costs per m\({}^{2}\) corresponding to the most relevant sets of measures which include the full amount to pay for energy consumption in 30 years for each m\({}^{2}\) (living area), the implementation of measures taken and maintenance. It also includes global cost per m\({}^{2}\) after 30 years of the initial state (L0), that is, if no action is taken, and identifies the full amount to pay for each m\({}^{2}\), especially energy consumption expenses.