## 3 Simulation Results and Analysis
### Internal Simulation Results  
Regardless of winter or summer, ventilation is necessary to ensure the freshness of indoor air. Therefore, the evaluation indicators for indoor air quality generally include air exchange rate and air age. Meanwhile, as indoor wind speed has a significant impact on people's activities, indoor airflow velocity is also one of the evaluation indicators in ensuring the freshness of indoor air. Based on the existing research results in Section 1, this study adopts 0.2-1 m/s as the indoor wind speed comfort evaluation index. The case project is located in Xi'an, where the dominant wind direction and wind speed are consistent in winter and summer, so there is no need to distinguish between winter and summer when evaluating indoor air quality. Figure 13 shows the indoor wind speed contour plots of each floor of the teaching buildings for the four scenarios, with the maximum wind speed regions marked by white dots. In order to facilitate comparisons among the four scenarios, the legends in Figure 13 were kept the same. In the corridor areas, the red portions with wind speeds greater than 1 m/s are mainly concentrated near the outer windows and doors facing the windward direction. The maximum wind speed in classrooms generally occurs near the classroom door and near the outer windows. In these areas, when the windows or doors are opened, the wind rushes in instantaneously. Coupled with the relatively small opening area, this creates a certain canyon wind effect, resulting in faster wind speeds. Subsequently, the wind speed gradually decreases, and in some areas, it gradually drops to a still-air state (wind speed less than 0.2 m/s). As the number of floors increases, the maximum indoor wind speed in the four scenarios also increases. After extracting the area proportions of each region, the results are shown in Figure 14. It can be seen that in Scenarios 2 and 3, the areas with wind speeds less than 0.2 m/s are larger, accounting for 18.30% and 10.25% of the total indoor area, respectively. In these areas, the airflow velocity is too slow, leading to poor indoor air quality due to the inability to update the indoor air in time. The areas with wind speeds less than 0.2 m/s in Scenarios 1 and 4 are significantly smaller than in Scenarios 2 and 3, accounting for 3.48% and 4.25%, respectively. Simultaneously, the proportion of areas with wind speeds greater than 1 m/s in Scenarios 1 and 4 is also lower than in Scenarios 2 and 3, accounting for 2.30% and 1.36% respectively. In summary, scenarios 1 and 4 provide better indoor wind environments in terms of indoor wind speed performance. Figure 15 displays the age distribution of air on each floor for the four scenarios. Typically, there is a direct relationship between air age and indoor airflow velocity, indicating that slower indoor airflow results in a higher air age, while faster flow leads to a lower air age. The indoor air quality conditions depicted in Figure 15 closely align with those in Figure 13. Scenarios 2 and 3 have a higher proportion of regions with slower internal airflow velocity, resulting in relatively higher air ages. The region with an air residence time ranging from 200 to 300 s is notably larger compared to Scenario 1. Although there is no significant difference in the proportion of stagnant areas between Scenario 4 and Scenario 1 (4.25% vs. 3.48%), the proportion of areas with an air age between 200-300 s in Scenario 4 is significantly higher than in Scenario 1. Therefore, Scenario 1 performs the best when evaluated from the perspective of air age. Figure 16 illustrates the air exchange rates in classrooms for the four scenarios. Scenarios 1 and 4, which showed superior indoor wind speed and air age performance, also exhibit higher indoor air exchange rates. Scenarios 2 and 3 have lower air exchange rates compared to Scenarios 1 and 4. Figure 14: Proportions of areas with wind speed not meeting the comfort criteria. Figure 13: Wind speed distributions inside school buildings.