# Thermal Comfort and Sustainability in University Classrooms: A Study in Mediterranean Climate Zones
## 3 Results
### Comfort Temperature
#### 3.4.1 Linear Regression Method  
The application of linear regression between thermal sensation votes and operating temperature facilitates the analysis of how variations in interior temperature affect occupants' thermal perception [22; 43]. Thus, Figure 6 shows the relationship between TSV and \(T_{\varphi}\) in each test, according to the thermal responses of the respondents in both modes of operation. From the linear equation, our temperature (\(T_{n}\)) and the temperature range where the votes are within the comfort range have been determined.  
As can also be seen in Table 8, the slope of the linear regression line for the NV mode was slightly steeper than that for the AC mode. This suggests that occupants are more sensitive to changes in operative temperature when natural ventilation is used. This increase in slope is attributed to the higher percentage of people who experienced discomfort, as assessed by the TSV scale. The slope values obtained in this study are consistent with those reported in research conducted in Mediterranean climate zones during the same time of year [22; 65; 66; 67]. However, they were lower than those observed in research conducted in warmer and more humid climates, highlighting the higher adaptation of students in these regions to higher temperatures. These findings highlight how regional  
Figure 5: Cross-tabulation of thermal preference votes on thermal sensation scale for (**a**) AC mode and (**b**) NV mode.  
In the AC tests, the \(T_{n}\), defined as the operative temperature at which the mean TSV is zero, was 25.80 \({}^{\circ}\)C. According to the 7-point scale of the ASHRAE 55 standard, the thermal acceptance range for 90% of the participants is between \(-\)0.5 and 0.5, which corresponded to a temperature range between 24.20 and 27.40 \({}^{\circ}\)C. For 80% acceptability, the range extends from \(-\)1 to 1, with temperature limits for this case between 22.60 and 29.00 \({}^{\circ}\)C. While in the NV mode, the \(T_{n}\) was 22.00 \({}^{\circ}\)C, with a comfort range of 90% acceptability between 20.00 and 24.00 \({}^{\circ}\)C and 80% acceptability between 18.00 and 26.00 \({}^{\circ}\)C. As can be seen, the \(T_{n}\) calculated for the AC tests is significantly higher compared to the NV tests. This could reflect that, in controlled environments, users have a higher tolerance to slightly higher temperatures [69, 70]. In the research carried out by [PERSON] et al. [71] and [PERSON] et al. [66] in this type of climate and with NV, temperatures very similar to those calculated in this work were obtained.  
Finally, the coefficients of determination (R\({}^{2}\)) were 0.2762 for the AC mode and 0.4754 for the NV mode, while the significance (\(p\)) values were less than 0.001 in both cases, indicating that the correlations between operative temperature and thermal sensation votes were statistically significant and adequate. The higher coefficient of determination obtained in NV mode indicates that operative temperature explains a higher percentage of the variability in wind chill votes compared to AC mode. This means the relationship between temperature and thermal perception is stronger and more consistent when using natural ventilation than when using air conditioning. This effect has been observed by other authors in studies conducted in areas with the same type of climate [37].  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Operation Mode** & **Equation** & \(T_{n}\) (\({}^{\circ}\)C) & **90\%** & **80\%** & **R\({}^{2}\)** & \(p\)-Value** \\ \hline AC & TSV = 0.2729-T\({}_{\text{op}}\)-7.0719 & 25.80 & \(\pm\)1.60 & \(\pm\)3.20 & 0.2762 & \(<\)0.001 \\ NV & TSV = 0.2864-T\({}_{\text{op}}\)-6.2608 & 22.00 & \(\pm\)2.00 & \(\pm\)4.00 & 0.4754 & \(<\)0.001 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Summary of TSV regression equations.  
Figure 6: Linear regression between the thermal sensation vote and operating temperature in (**a**) AC mode and (**b**) NV mode.