# Effects of Night Ventilation on Indoor Air Quality in Educational Buildings--A Field Study
## 2 Materials and Methods
### Measurements
#### 3.1.2 Indoor Microbial Concentrations  
Figure 4 normalizes the indoor microbial concentration in buildings 1-3 with the average CO\({}_{2}\) concentration (mean \(\pm\) sd), relative humidity, and air temperature measured from a height of 1.1 m. Microbial results are normalized over the pre-started ventilation content to show a change between the test cases. Those results represent an observed trend in the pre-started, continuous, and intermittent night ventilation methods related to space usage, thermal conditions, and humidity levels during each 2-week dust collection period. Generally, the results show that these parameters had no systematic effect on microbial change. Figure 5 shows box-plot patterns from a comparable sample of objects classified by the microbial group. The sample includes the primary schools 1-2, the kindergartens 1-3, and the university building. In the Unifung group, the mean concentration decreased by 23% and the standard deviation by 21% with the continuous ventilation compared to the pre-started ventilation. Furthermore, the intermittent ventilation decreased the mean unifying content by 37% and the standard deviation by 57% compared to pre-started ventilation. Consequently, the pre-started ventilation increased the total fungal content compared to continuous and intermittent use of night-time ventilation. Figure 3: Indoor/outdoor-ratio of the microbial content of the settled dust collected during two weeks. Building 1: group workspace in university building in spring. Building 2: classroom in primary school 3 in spring. Building 3: playroom in kindergarten 3 in summer. Building 4: playroom in kindergarten 5 in summer. Building 5: classroom in primary school 4 in autumn. Building 6: playroom in kindergarten 4 in autumn reflecting natural variation (both test cases are similar). Building 7: classroom in primary school 1 in winter. Building 8: playroom in kindergarten 2 in autumn. Building 9: classroom in secondary school in late autumn. In the Pen/Asp group, the lowest mean concentration was observed when the night ventilation was not used at night. One probable reason could be that outdoor air is a typical source of those species, and therefore, the concentration was smaller. Continuous ventilation increased the mean Pen/Asp concentration by 31% and intermittent even multiplied the mean concentration compared to the pre-started ventilation, but the result  
Figure 4: The normalized indoor microbial content [-] related to average CO\({}_{2}\) [ppm], relative humidity [%], and indoor air temperature [\({}^{\circ}\)C] classified as microbial group. Building 1 is the university building, building 2 is the primary school 3, and building 3 is the kindergarten 3. CO\({}_{2}\) is the carbon dioxide concentration (avg \(\pm\) sd), RH is the relative humidity, and temp is the indoor air temperature measured at the height of 1.1 m. The vertical axis on the left is the normalized concentration and the vertical axis on the right is the compared physical quantity, ref is the minimum level, i.e., the background CO\({}_{2}\) level (400 ppm). Figure 5: The indoor microbial content [CE/m\({}^{2}\)-d] of settled dust collected during two weeks (\(n=6\)). The sample includes the primary schools 1–2, the kindergartens 1–3, and the university building. was affected by one exceptionally large sample. The standard deviation was roughly two times higher with continuous ventilation compared to pre-started ventilation. Hence, the pre-started ventilation decreased the fungal content in the _Penicillium_, _Apergillus_, and _Paecilomyces variotii_ group compared to continuous and intermittent use of nighttime ventilation. In the Grampos group, the mean concentration decreased by 5% and the standard deviation by 9% with the continuous ventilation compared to the pre-started ventilation. The intermittent ventilation decreased the mean content by 31% and the standard deviation by 35%, correspondingly.