## 2 Materials and Methods
### Methodology
#### 2.3.1 Case Study  
The study focuses on a classroom in a school building in the city center of Sevilla (Spain). It is placed at 37.39 north latitude, and 5.98 east longitude, and influenced by a subtropical climate, Cas in the Koppen-Geiger classification [46]. The average temperatures are 11.3 \({}^{\circ}\)C in December, 25.7 \({}^{\circ}\)C in June, and 18.2 \({}^{\circ}\)C for the whole year. The average humidities are 75% in December and 42% in June. The prevailing winds are southwest in summer and northeast in winter.  
This classroom has been selected because it is representative of the average school buildings in this region, but also because it has already been used in previous studies of IAQ and TC [7]. The distribution and position of the different elements within the classroom are presented in Figure 3.  
* Figure 3a provides a layout with the position of the openings and the seats for the occupants. It also contains the position of the radiators (in red) and the heat pump (in blue). There is only 1 entrance to the classroom, which was always closed during the experimentations. The graphic scale and the north compass sign are included to classify the window openings as north/south. The north facade can be described as windward, while the south facade is considered leeward for the purposes of cross-ventilation analysis.
* Figure 3b provides an axonometric 3D view of the room, which adds extra information. Both windward and leeward openings include a set of solar-protection louvres, but during winter they are always set at a horizontal position. Therefore, it is considered that they have no influence on the ventilation process. Blue boxes describe the split heat-pump system. The yellow dot describes the approximate position of the IAQ monitoring devices (Figure 4a), while the yellow line describes the wireless connection with the central console (Figure 4b).  
The classroom volume is 141.36 m\({}^{3}\). It is usually occupied by 25 pupils of about 11 years old and a teacher, which makes one person every 1.90 m\({}^{2}\) (see Table 2), for the main parameters. The classroom activity schedule is organized from Monday to Friday. The attendance hours are from 9:10 to 12:05 and from 12:30 to 13:55. Students have a playtime out of the room between 12:05 and 12:30.  
Figure 3: Opening elevation layout (**a**) and _DesignBuilderTM_ model 3D view (**b**).  
Construction elements were reviewed on-site and their thermal transmittance and other physical properties were calculated using _DesignBuilderTM_. No insulation materials were found during the visual inspection, as would be expected for a 1970s building. The roof is composed of two separate layers with a non-ventilated interior air cavity of 0.60 m average thickness. Ceiling and flooring both include a concrete slab. The external walls are composed of two bricks sheets with an interior variable-thickness air cavity (cavity thickness from 5 to 15 cm). The windows in the south and north facades include aluminum frames plus double-glazing panes with air-gap insulation, as described in Table 2 (thermal transmittance), which gives a thermal summary of these construction elements.  
The classroom is cross-ventilated through the windows in both the windward and leeward facades, as shown in Figure 4a. Both show, in red, the maximum effective opening to be considered for natural ventilation following the definition of the WWeqR.