## 2 Materials and Methods
### Cost Optimisation Methodology
#### 2.1.2 Energy Efficiency Measures and Sets of Measures  
This study is focused on proposing passive renovation measures, that is to say, measures to implement in the thermal envelope, so renewing air conditioning system, ventilation, lighting, renewable energy, etc., is not considered. The buildings selected represent a group of school buildings according to specific architectural aspects, but many of them are part of a school complex, where other buildings are introduced, such as classrooms, canteens, gymnasiums, etc. This involves that requirements differ according to different typology, although the design and construction time of the main building are similar. On the other hand, facility renovations are driven by the time when the existing ones break down or when a necessary renovation due to obsolescence is convenient and affordable. It would be unrealistic to plan the sudden replacement of all the facilities existing in school buildings. For all these reasons, the energy renovation measures proposed are aimed at reducing the energy demand in buildings. The passive measures outlined are window and door replacement (W), including solar protection elements, and insulation upgrading in facades (F) and roofs (R). These measures \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Thermal Envelope Element** & **Type A** & **Type B** & **Type C** \\ \hline Construction date & 1947 & 1957 & 1975 \\ \hline Constructed area & 1634.77 m\({}^{2}\) & 1002.70 m\({}^{2}\) & 2595 m\({}^{2}\) \\ \hline Living area & 785.89 m\({}^{2}\) & 525.42 m\({}^{2}\) & 1993.27 m\({}^{2}\) \\ \hline Number of floors & 2 & 3/4 & 2 \\ \hline Climate zone & B3/IV & B3/IV & B3/IV \\ \hline Use & 8 h & 8 h & 8 h \\ \hline Roofs & Curved ceramic roof tiles over ceramic brick board, wooden & Ceramic tiles, mortar, ceramic & Ceramic tiles, mortar, \\  & structure, highly ventilated air & brick boards, waterproof & waterproof protection, \\  & chamber, false ceiling made of & chamber, reinforced with & reinforced with concrete slab \\  & cane, plaster. & concrete slab floor, plaster. & floor, plaster. \\ \hline Facades & Rendering mortar, brick wall & Rendering mortar, double & Double perforated brick wall with a vertical air chamber \\  & (thickness: 40 cm/50 cm), & vertical air chamber & \\  & plaster. & (11 + 5 + 4 cm), plaster. & (11 + 7 + 7 cm), plaster. \\ \hline Windows and doors & Wooden windows and metal & Wooden windows and metal & Metal single-glazed windows & and doors. Rolling shutter \\  & single-glazed doors & & Central heating through diesel \\ \hline Heating System & Electric radiator/s in each room & Electric radiator/s in each room & oil boiler with multiple water \\  & room & room & circulation pumps and iron \\  & & radiator/s in each room \\ \hline Hot Water System & Electric hot water boiler for kitchen and pre-school toilets & Electric hot water boiler for & Electric hot water boiler for \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Thermal transmittance, U (W/m\({}^{2}\)K), of construction elements in thermal envelope of representative school buildings in their initial state L0. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Thermal Envelope Element** & **Type A** & **Type B** & **Type C** \\ \hline Facades & 1.1/0.92 & 2.94/1.33 & 1.41/1.29 \\ Roofs & 4.17 & 2.33/1.79 & 1.79 \\ Windows (single glazed/structure) & 5.7/2.2 & 5.7/2.2 & 5.7/5.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specifications and characteristics of building types. can be implemented separately or combined with each other, resulting in the improvement of seven elements or combinations of elements of the thermal envelope. In addition, three levels of energy demand are considered in relation to the transmittance of thermal envelope elements (L1, L2 and L3). These values are set according to specific regulatory requirements. In particular, the intermediate level, L2, includes the minimum values set by current Spanish regulations on energy efficiency, the CTE DB-HE 2019 [22].