# Keeping Doors Closed as One Reason for Fatigue in Teenagers--A Case Study
## 4 Discussion  
To ensure that the CO\({}_{2}\) concentration is at a lower level, it is necessary to supply an adequate amount of fresh air instead of used air. [PERSON] et al. [38] summarised that the most influential variables on the air change rate (ACR) are room volume, number of individuals sleeping in the bedroom, average window and door opening habits, location of the measured room (ground or higher floor), and year of building construction. The authors underlined that more door opening results in a higher air change rate. Our study was performed in two similar bedrooms occupied by girls aged 13 and 9 years old. Due to a low IAQ outside the building, the window opening was very limited; thus, we focussed on door opening and compared it with subjective evaluation of sleep satisfaction. Research by [PERSON] et al. [38] revealed that, when the bedroom doors are air or fully open instead of closed, the ACR increases from 0.48 to 0.55 (14%) and 0.71 (48%). Although we did not calculate the ACH, the observed decrease in CO\({}_{2}\) concentration while keeping the bedroom doors open during the night was 55% and 64% in the teenager's and the child's bedroom, respectively. Generally, adults appear to be additional immune to the consequences of sleep deprivation, whereas children, teenagers and particularly young children tend to be a vulnerable subpopulation as they spend the majority of their time indoors at home while their respiratory and other systems are under development [8]. When an individual does not get enough sleep to feel awake and alert, they begin to experience symptoms of sleep deprivation such as yawning, irritability, fatigue, inability to concentrate, moodiness, forgetfulness, lack of motivation, depression, and poor perspective on life [3]. In our study, the average concentration during the night was similar in both bedrooms, at 1077 ppm (teenager) and 1103 ppm (child), which is comparable with the average CO\({}_{2}\) concentration in unoccupied bedrooms (999 ppm and 1236 ppm in South and North bedrooms, respectively) as reported by [PERSON] et al. [25]. In occupied bedrooms, the authors in [25] reported higher (1585 ppm and 1760 ppm in South and North bedrooms, respectively) than our average concentration of CO\({}_{2}\), which was 766 ppm and 860 ppm with open doors and 1402 ppm and 1337 ppm with closed doors, in the teenager's and the child's bedroom, respectively (Figure 3). However, it is similar to the average CO\({}_{2}\) concentration of 716 ppm measured in 13 bedrooms located in Athens' residences [39]. During the night with the doors closed, in the teenager's and the child's bedroom, 48% and 43% of CO\({}_{2}\) concentration measurements were higher than 950 ppm above outdoor CO\({}_{2}\) concentration (398 ppm), which corresponds to category IV-low indoor environment quality (IEQ\({}_{\text{IV}}\)), and, when open, it was \(<1\%\) in both bedrooms. The PN-EN 16798-1 standard [20] underlines that a lower level will not provide any health risk but may decrease comfort. At the same time, the categories are related to the levels of expectations. A normal level would be medium, but, for occupants with special needs (children, elderly, persons with disabilities, etc. ), a higher level might be selected. During the research with opened doors, a high IEQ prevailed during 51% of the night in the teenager's bedroom, and during 26% of the night in the younger girl's bedroom. In comparison, the authors in [25] reported that time spent by an occupant in a CO\({}_{2}\) concentration over 1500 ppm in a mechanically ventilated detached house was approximately 30% of an entire day; thus, the IEQ in researched bedrooms could be satisfying with the door open; however, only the younger girl evaluated sleep satisfaction as high (16%). The subjective assessment of sleep satisfaction points to a lower IEQ in the case of the older girl's bedroom, which can be supported by a greater CO\({}_{2}\) concentration range (Figure 2) in the teenager's bedroom.