# Thermal Comfort and Sustainability in University Classrooms: A Study in Mediterranean Climate Zones
## 2 Materials and Methods
### Application of Questionnaires and Indoor Thermal Measurements  
The data collection, which included both environmental measurements and the application of questionnaires, was carried out during the last weeks of the 2021-2022 academic year, specifically from 6 to 17 June, during class hours (9:00 a.m. to 4:00 p.m.). The questionnaires were distributed and explained at the beginning of the lessons but were completed at the end so that the participants could evaluate how they had felt during the class.  
Measurements of indoor environmental parameters were performed close to the students, avoiding any disturbance to the normal course of the classes [43]. These mea  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**University**} & \multirow{2}{*}{
\begin{tabular}{c} **No. of Classrooms** \\ **Studied** \\ \end{tabular} } & \multicolumn{2}{c}{**No. of Students**} & \multirow{2}{*}{**Operation Mode**} \\ \cline{3-3} \cline{5-5}  & & **Max.** & & **Min.** \\ \hline \multirow{2}{*}{ESE} & 7 & 42 & 9 & NV \\  & 4 & 17 & 6 & AC \\ \multirow{2}{*}{ESS} & 2 & 30 & 20 & NV \\  & 2 & 20 & 13 & AC \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of the classrooms in the study.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Scale** & **Thermal Sensation (TS)** & **Thermal Comfort (TC)** & **Thermal Preference (TP)** \\ \hline \(-3\) & Cold & & \\ \(-2\) & Cool & & \\ \(-1\) & Slightly cool & & Cooler \\ \(0\) & Neutral & & No change \\ \(1\) & Slightly warm & Very comfortable & Warmer \\ \(2\) & Warm & Comfortable & \\ \(3\) & Hot & Slightly uncomfortable & \\ \(4\) & & Uncomfortable & \\ \(5\) & & Very uncomfortable & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Subjective thermal comfort scales.  
surements were carried out throughout the duration of the tests from the time the students entered the classrooms. Air temperature (\(T_{a}\)), relative humidity (\(RH\)) and air velocity (\(v_{a}\)) were measured using an HD32.1 thermal environment analyser (DeltaOhm), which complies with the accuracy ranges of ISO 7726:1998 [44]. This equipment was placed in the centre of each of the classrooms studied, with the aim of representatively assessing the microclimate in the classrooms [22; 44; 45]. The mean radiant temperature (\(T_{mt}\)) was calculated, following the recommendations of ASHRAE 55 [2], with Equation (1). This calculation was based on the globe temperature measurement (\(T_{g}\)) obtained using a black globe thermometer with a diameter of 150 mm.  
\[T_{mrt}=\left[\left(T_{g}+273\right)^{4}+\frac{1.1\cdot 10^{8}\cdot v_{a}^{0.6} }{\varepsilon\cdot D^{0.4}}\cdot\left(T_{g}-T_{a}\right)\right]^{1/4}-273 \tag{1}\]  
where \(\varepsilon\) is the emissivity of the surface of the globe thermometer and \(D\) is its diameter, being 0.95 and 0.150 metres, respectively.  
Table 3 provides the technical specifications of the equipment used for the measurements of indoor environmental conditions.  
On the other hand, the comfort temperature (\(T_{c}\)) is related to the operative temperature (\(T_{op}\)) and the mean outdoor operating temperature (\(T_{m}\)). As shown in Equation (2), the calculation of \(T_{op}\) considers air temperature (\(T_{a}\)), mean radiant temperature (\(T_{mrt}\)), convective heat transfer coefficient (\(h_{c}\)) and radiant heat transfer coefficient (\(h_{r}\)) [2; 47]. For \(h_{r}\), a constant value of 4.7 W/m\({}^{2}\)\({}^{\circ}\)C was taken, while \(h_{c}\) was calculated according to the ASHRAE Handbook [48].  
\[T_{op}=\frac{T_{a}\cdot h_{c}+T_{mrt}\cdot h_{r}}{h_{c}+h_{r}} \tag{2}\]  
In turn, the mean outdoor operating temperature (\(T_{m}\)) was determined with Equation (3) [49; 50].  
\[T_{m}=(1-\alpha)\cdot\left\{T_{out,n-1}+\alpha\cdot T_{out,n-2}+\alpha^{2} \cdot T_{out,n-3}+\cdots\right\} \tag{3}\]  
where \(T_{out,n-x}\) is the daily average outdoor temperature of day \"\(x\)\" days before day \"\(n\)\" [50]. According to EN 16798-1:2020 [51], a value of 0.8 was taken for \(\alpha\).