## 2 Materials and Methods  
### Description of the Studied Buildings  
The example buildings considered in this study are two similar five-story apartment buildings which locate in Helsinki, Finland. The geometry and orientation of the example buildings are identical (Figure 1). The facade with the largest windows fronts west. However, some simulation cases are defined with different orientations. The buildings have four living floors and a basement floor which is located underground, containing storage and technical spaces. The heated net floor area of the buildings is 1943.5 m\({}^{2}\). It is assumed that the example buildings are located in a neighborhood, where they are surrounded by similar buildings (Figure 2). Figure 1: The geometry of the building. Figure 2: The location of the simulated example building (black box) and the surrounding buildings (grey boxes). The new building is assumed to be built after 2012 while the old building belongs to the 1960s. Thus, ventilation systems, envelope properties, window to wall ratio, and window properties are different according to the common practice of the construction year. The envelope properties of the old and new buildings, including the U-values and window properties, are reported in Table 1. The floor plan and room types of the buildings are shown in Figure 3.  
To facilitate the comparison of the results, the properties of the buildings and the HVAC system are assumed to be the same in the simulations of current and future climate conditions even if the efficiencies of the cooling systems may improve in the future. The ventilation system in the old apartment building is a constant air ventilation (CAV) mechanical exhaust system. The specific fan power (SFP) of the ventilation system \begin{table}
\begin{tabular}{c c c} \hline \hline
**Description** & **Old Apartment Building** & **New Apartment Building** \\ \hline Time of Construction & The 1960s & After 2012 \\ Construction & Concrete & Concrete \\ Number of residential floors & 4 & 4 \\ Number of apartments & 20 & 20 \\ Air leakage rate q\({}_{50}\) (m\({}^{3}\)/h m\({}^{2}\)) & 6 & 2 \\ Window to wall ratio (\%) & 19 & 15 \\ Window Properties & & \\ U- value (W/m\({}^{2}\)K) & 2.5 & 1 \\ Total solar heat transmittance (g) & 0.76 & 0.35 \\ Direct solar transmittance (ST) & 0.7 & 0.3 \\ Average U- value of external walls (W/m\({}^{2}\)K) & 0.6 & 0.17 \\ Integrated shading & \begin{tabular}{c} Manually controlled blinds between the outer panes, according to the occupancy profile and the intensity of solar radiation (>100 W/m\({}^{2}\)). \\ Window indentation 30 cm \\ District heating, 40/70 \({}^{\circ}\)C water \\ radiators, 100 W/m\({}^{2}\) \\ \end{tabular} & \begin{tabular}{c} Window indentation 5 cm \\ District heating, 40/70 \({}^{\circ}\)C water \\ radiators, 65 W/m\({}^{2}\) \\ \end{tabular} \\ \begin{tabular}{c} Mechanic cooling system (optional) \\ \end{tabular} & \begin{tabular}{c} Split unit in each living room, SCOP: 3, 45 W/m\({}^{2}\) \\ \end{tabular} \\ \begin{tabular}{c} Ventilation \\ \end{tabular} & \
\begin{tabular}{c} Mech. Exhaust (CAV) \\ \end{tabular} &
\begin{tabular}{c} Balanced Mech. ventilation (CAV) \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Construction properties of the basic form of the old and new example apartment buildings. Figure 3: Floor plan and room types in the old and new apartment building, the exhaust airflow rates of the old building, and the air flow rates of the new building. is 0.7 kW/m\({}^{3}\)/s. The exhaust airflow rates (negative values) in different rooms of the old apartment building are shown in Figure 3. The air leakage rate of the building envelope q\({}_{50}\) at 50 Pa pressure difference is 6 m\({}^{3}\)/hm\({}^{2}\). The ventilation system of the new apartment building is CAV mechanical supply and exhaust ventilation system.