## 4 Methodology  
To provide a comprehensive comparison of ventilation systems according to the aforementioned quality standards, it was necessary to devise a standardized process that ensures uniformity across all systems. This protocol was implemented to obtain the most precise and reliable data for analysis. The ventilation systems, specifically System#1, System#2, System#3, and System#4, underwent testing in a primry school located in Bucharest. The installation of all equipment took place on the ground floor of the building, namely in classrooms that have comparable capacities. A multitude of sensors was deployed within these rooms. In order to conduct data analysis, our attention will be directed towards the sensors located in the central area of each classroom, specifically in close proximity to the video projector. Other CO2 sensors were placed on the walls and in the back of the room at normal height (approx. 1.5 m). For the measurements, the ARANET CO2 monitors have been used as an advanced and accurate device specifically engineered for the purpose of detecting carbon dioxide concentrations in diverse settings. The device has a large measuring range ranging from 0 to 9999 ppm, rendering it appropriate for a diverse range of applications, encompassing educational settings, as well as industrial situations. The monitor's elevated resolution of 1 part per million (ppm) enables the precise and comprehensive monitoring of carbon dioxide (CO2) levels. The device exhibits a level of precision with regards to accuracy, adhering to a standard of \(\pm\)30 ppm or \(\pm\)3% of the measured value, thereby guaranteeing the dependability of the collected data. The time constant \(\tau\), which represents 63% of the total response time, is set at 100 s. This number represents the sensor's capacity to rapidly detect and communicate changes in CO2 levels, hence guaranteeing timely and precise information about air quality. Furthermore, the ARANET CO2 monitor is equipped with the ability to measure temperature, including a range from 0 to 50 \({}^{\circ}\)C and boasting a precise resolution of 0.1 \({}^{\circ}\)C. The temperature readings exhibit a high level of precision, with a margin of error of \(\pm\)0.3 \({}^{\circ}\)C. The device is capable of quantifying relative humidity within a specified range of 0-85%. It achieves this with a resolution of 1% and an accuracy of \(\pm\)3%. To evaluate the efficacy of the equipment, an additional sensor was set up within a classroom without ventilation, alongside an external sensor to quantify the ambient air quality surrounding the building. The present study will examine the variations in humidity, temperature, and CO2 levels over a duration of one month. This period coincides with the presence of children in the classroom for five \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ventilation System** & **Single-Flow CMV** & **Decentralized Double-Flow** & **Classic Double-Flow Ventilation** \\ \hline \multirow{8}{*}{Disadvantages} & The system creates a depression in the room, causing cold air to enter and excess heating consumption. & & \\  & & Maintenance must be carried out & \\  & & on each piece of equipment. & \\  & & It is still a very recent technology, & \\  & & making the question of & \\  & Cold drafts in rooms. & repairability difficult to assess. & \\  & & Requires multiple openings in the & \\  & & facade to supply the groups. & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: \(Cont.\)consecutive days each week, while they remain at rest during the weekends. We shall do a comparative analysis of the data both internally and in relation to the external sensor. To assess the level of comfort in a room and consequently the level of contentment among occupants, a subsequent set of measurements was carried out on 15 February 2023 in the morning. This was performed in four ventilated rooms utilizing a Testo440 sensor along with its corresponding probes.