## 3 Results
### Close-Agreement Analysis between DYU Air Box and Commercial Instruments
Furthermore, Figure 8g,h reveal the temperature and humidity measurement differences between the DYU Air Box and TES-1364 temperature and humidity meter. Figure 8g illustrates the temperature differences between the DYU Air Box and measurement instrument, with a difference range of \(-\)0.1758-0.2280 \({}^{\circ}\)C and the corresponding MAE and RMSE of 0.10 \({}^{\circ}\)C and 0.12 \({}^{\circ}\)C, respectively. The temperatures between the BME680 sensor in the proposed DYU Air Box and TES-1364 instrument are 99.34% similar with a MAPE value of 0.66%. Moreover, the humidity difference between the DYU Air Box and TES-1364 humidity meter is shown in Figure 8h, with a difference range of \(-\)0.3894-0.2767% over a 24 h measurement period and MAE, RMSE, and MAPE values of humidity analysis of 0.16%, 0.19%, and 0.31%, respectively. The sensing ability of the BME680 sensor of the proposed DYU Air Box has a close agreement of 99.60% withthe commercially available TES-1364 humidity meter. The comfort level in the classroom such as illumination, ambient temperature, and humidity can be well monitored by the proposed DYU Air Box like the commercialized instruments. Figure 8: _Cont._  
Figure 8: _Cont_. Figure 8: _Cont._  
Figure 8: Difference analysis of 24 h in situ measurement results for DYU Air Box compared with corresponding measurement instruments: (**a**) IAQ index; (**b**) IAQ level; (**c**) PM\({}_{1.0}\) concentration; (**d**) PM\({}_{2.5}\) concentration; (**e**) CO\({}_{2}\) concentration; (**f**) brightness; (**g**) temperature; (**h**) humidity. The TES-1337B light intensity meter and TES-1364 temperature/humidity meter were tested. The close-agreement analysis for the proposed DYU Air Box and the corresponding measurement instruments are tabulated in Table 5 in detail. According to the above statistical analyses of measurement results, the MAPE values of the AQI index/level, PM\({}_{1.0}\) and PM\({}_{2.5}\) concentrations, CO\({}_{2}\) concentrations, brightness, ambient temperature, and humidity are less than 0.5%, i.e., the sensing accuracy of the DYU Air Box has similarity to the above commercialized measurement instruments of up to 99.5%. The indices of indoor air quality and comfort level including AQI index/level, PM\({}_{1.0}\) and PM\({}_{2.5}\) concentrations, CO\({}_{2}\) concentrations as well as brightness, ambient temperature, and humidity can be monitored using the proposed DYU Air Box with sufficient accuracy and confidence that are the same as those of commercialized instruments. The proposed DYU Air Box features the integration of multiple, heterogeneous sensors using I\({}^{2}\)C and UART standard communication interfaces. It should be noted that the surrounding environmental conditions can significantly affect the ones in the H708 classroom from the viewpoint of system dynamics. As shown in Figure 7g, the incoming of solar irradiance increases the brightness which might have a positive effect on learning regarding indoor illumination and food quality. The solar irradiation simultaneously increases the indoor temperature of the classroom and increases the load of air conditioners. Therefore, a curtain shield is necessary for the comfort of classmates during class hours, and this could save the electricity consumption of air conditioners. Furthermore, Figure 7a,h reveal the close correlation between AQI value and humidity; therefore, suitable dehumidification is suggested to keep good indoor air quality. Furthermore, air purifiers can effectively remove PM\({}_{2.5}\) as shown in Figure 7d. The findings of a mutual effect between AQI value/level and RH, as well as a positive effect of PM\({}_{2.5}\) purification by HVAC, can be adopted to improve AQI level. It should be noted that HVAC operation has no effect on the PM\({}_{1.0}\) removal.