## 2 Materials and Methods
### A Description of the Residential Apartment Unit for the Energy Retrofitting Project
The impact of seasonality is considered a critical source for generating uncertainty in energy calculations. Passive heating and cooling are at the core of the design strategy and are pursued to exploit the benefits of natural light, ventilation, and temperature. On the other hand, an apartment's thermal performance is affected by the orientation of the external window shading (facades, shutters, roll-blinds, or overhangs) as well as the peripheral topography of the adjacent building structures and neighboring trees. Finally, the nominal data for the electromechanical systems and the accompanying equipment of the examined apartment unit are listed in Table 3. The heat generation system is a centralized network that separately feeds the terminal heat outlets in all apartment units. It is oil-fueled and thermostat-controlled. It uses the one-pipe distribution mode to circulate the heated body of water. On the contrary, there is no central cooling system. Instead, electrical and pump-driven air-conditioning units provide the local cooling load, which is intended to cover about 50% of that total apartment area. Hot water generation was provided by a double-sourced boiler. It operates using electricity and solar energy. Solar energy is directly collected from roof-top solar panels. Hot water is maintained in a storage tank that hydrostatically circulates to the apartment unit. The solar panel system data are tabulated in Table 3.  
Figure 4: Structural elements for the examined apartment unit. Figure 5: Configuration of the examined apartment unit with respect to the neighboring construction. Figure 3: Floor plan for the examined apartment unit. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Flat Surface Area (m2)**} \\ \cline{2-7}
**Floor Level** & **Heated** & **Non-Heated** & **Total** & **Balcony** & **Cooled** & **\% Non-Heated** & **Height (m)** \\ \hline
**Underground** & & 29.95 & 29.95 & & 0 & 100 & 2.6 \\
**Ground** & 56.66 & 8.17 & 64.83 & 276 & 21.17 & 12.6 & 3.15 \\ \hline
**Upper** & 100.83 & 4.37 & 105.2 & 158.61 & 50.42 & 4.15 & 3.1 \\
**Loft** & **0** & 21.35 & 21.35 & 158.61 & **0** & 100 & 2.2 \\
**Totals** & 560.81 & 81.32 & 642.13 & 1227.66 & 273.24 & 17.02 & 23.45 \\ \hline \multicolumn{7}{c}{**Flat Volume (m3)**} \\ \cline{2-7}
**Floor Level** & **Heated** & **Non-Heated** & **Total** & **Cooled** & **Perimeter (m)** & **Exterior Wall Area (m2)** \\ \hline
**Underground** & **0** & 77.87 & 77.87 & **0** & **22.34** & & 58.08 \\ \hline
**Ground** & 178.48 & 25.74 & 204.22 & 89.24 & 38.3 & & 120.65 \\
**Upper** & 312.57 & 13.55 & 326.12 & 156.29 & 50.44 & & 156.36 \\
**Loft** & 0 & 46.97 & 46.97 & 0 & 19 & 41.8 \\
**Totals** & 1741.34 & 238.31 & 1959.65 & 870.67 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Basic area parameters of the apartment building shell. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & \multicolumn{1}{c}{**Orientation**} & \multicolumn{1}{c}{**Total Area**} & \multicolumn{1}{c}{**Window Frames**} & \multicolumn{1}{c}{**Walls Area (m2)**} & \multicolumn{1}{c}{**U Wall**} \\ \cline{2-7}
**Wall no. 1** & 30 & 37.2 & 8.8 & 28.4 & 0.563 \\ Wall no. 2 & 120 & 27.75 & & 27.75 & 0.522 \\
**Wall no. 3** & 210 & 26.35 & 8.12 & 18.24 & 0.521 \\
**Wall no. 4** & 300 & 33.33 & & 33.33 & 0.523 \\
**Stairway/elevator** & **0** & 29.37 & 1.8 & 27.57 & 0.261 \\
**Loft** & 0 & 99.43 & & 99.43 & 0.44 \\ \hline
**Maintenance** & **0** & **5.77** & & **5.77** & **0.22** \\
**room** & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Basic wall parameters of the building shell. Figure 6: Side shadings for the examined apartment unit (left drawing: summer season, right drawing: winter season).