# Keeping Doors Closed as One Reason for Fatigue in Teenagers--A Case Study
## 3 Results  
As mentioned above, proper ventilation controls IAQ. Among the techniques adopted to evaluate ventilation rates, the one based on the measurement and analysis of the indoor CO\({}_{2}\) concentration and trends is the most common approach; however, it could be improved by the integration of an electronic nose for odor detection [35]. Acceptable ventilation conditions can be easily achieved in mechanically ventilated rooms, but it is not equally simple to maintain CO\({}_{2}\) and odor levels under control in indoor environments that are naturally ventilated [35]. Natural ventilation is typical for detached buildings in Poland, where the ventilation and the IAQ are controlled only by means of air infiltration through cracks and openings. The IAQ gets worse during the winter season when the desire for thermal comfort and acceptable IAQ are in conflict. For the characterization of IAQ by measuring CO\({}_{2}\) concentration, several indicators and criteria can be used [25]. We selected the average CO\({}_{2}\) concentration and a time fraction over a limit of \(\Delta\)CO\({}_{2}\) values spent during the night according to the PN-EN 16798 standards [20,21]. Figure 2 shows the field measurements in the teenager's and child's bedrooms, including the CO\({}_{2}\) concentration range, when the doors were open and closed. During the night, the short-term (60 s average) concentrations varied from 402 to 3320 ppm in the teenager's bedroom and from 458 to 2176 ppm in the child's bedroom. Thus, the highest concentrations exceeded the limits characteristic of subjective symptoms such as fatigue, headaches, and an increased perception of warmth and unpleasant odors [14]. If we compare the data separately by day of the week (Table 1), it is clear that, despite similar average concentrations, the maximum concentrations were significantly higher in the teenager's bedroom. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{6}{c}{**CO\({}_{2}\) Concentrations, ppm**} \\ \cline{2-7}  & \multicolumn{3}{c}{**Teenager’s Bedroom**} & \multicolumn{3}{c}{**Child’s Bedroom**} \\ \cline{2-7}  & **Average** & **Minimum** & **Maximum** & **Average** & **Minimum** & **Maximum** \\ \hline Monday & 1127 & 402 & 3102 & 1828 & 1828 & 1828 \\ Tuesday & 998 & 597 & 2336 & 1114 & 554 & 1855 \\ Wednesday & 1088 & 452 & 2897 & 1144 & 458 & 1855 \\ Thursday & 1199 & 411 & 2695 & 1118 & 688 & 1778 \\ Friday & 1195 & 479 & 3320 & 1076 & 563 & 1757 \\ Saturday & 3061 & 3061 & 3061 & 1262 & 599 & 2176 \\ Sunday & 1191 & 405 & 3188 & 1993 & 1993 & 1993 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Average, minimum, and maximum CO\({}_{2}\) concentrations according to the day of the week. Figure 2: CO\({}_{2}\) concentration inside the teenager’s and child’s bedrooms during the night. Distinguishing between open and closed doors in the teenager's and child's bedrooms, the average nightly concentrations were not significantly different (\(p\) = 0.76; 1077 and 1103 ppm, respectively); however, there was a statistically significant difference in CO\({}_{2}\) concentration between bedrooms with open and closed doors (Figure 3). In the teenager's bedroom, opening the doors during the night decreased the average CO\({}_{2}\) concentration by 55%, and in the child's bedroom, the observed decrease was 64%. Moreover, room temperature and humidity are important factors that may influence perceived environment quality. They both affect the thermal balance of the human body through effects on the skin and respiratory organs. Changes in air temperature trigger a sympathetic reflex via the skin that strengthens with lower air temperature. High temperatures and humidity require the human body to respond by increasing heat loss through the skin surface via blood circulation. The relation between indoor temperature and humidity depends on the season and indoor conditions [36].