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Window typology as a determinant of indoor air quality in naturally ventilated tropical African offices
Amaka-Anolue Martha Basil1, Chiamaka Christiana Okwuosa1, Ejike Kingsley Anih1
1Department of Architecture, Faculty of Environmental Studies, University of Nigeria, Nsukka, Nigeria.
Abstract:
Indoor air quality (IAQ) is a critical determinant of health and productivity in tropical African office environments where natural ventilation is the primary ventilation strategy, yet the influence of architectural factors such as window typology remains understudied. This study examined how casement, projecting, and louvered window systems, along with associated architectural features, affect measured IAQ in naturally ventilated government offices in Enugu, Nigeria. Using a cross-sectional observational design, the study assessed 54 offices and measured carbon monoxide (CO), carbon dioxide (CO2), formaldehyde (HCHO), total volatile organic compounds (TVOC), particulate matter (PM2.5), temperature, and relative humidity (RH). Data were analyzed with ANOVA and multivariate linear regression to isolate the effects of window typology while controlling for structural covariates like headroom, floor area, occupancy, etc. Significant IAQ differences were observed across window types, and the multivariate models identified window typology as a robust predictor for HCHO, RH and PM2.5. Casement windows consistently produced the most favourable IAQ profile, yielding the lowest adjusted pollutant concentrations. Compared to casement windows, projecting windows were associated with higher RH (B = 3.61%, p = 0.003), higher PM2.5 (B = 3.17 µg/m3, p = 0.005), and higher HCHO (B = 0.012 mg/m3, p = 0.019). Similarly, combined louvered + projecting windows were associated with significantly higher RH (B = 1.64%, p = 0.045), PM2.5 (B = 2.19 µg/m3, p = 0.005), and HCHO (B = 0.008 mg/m3, p = 0.021) than casement types. Adjusted PM2.5 was lowest in casement offices (3.83 µg/m3), while projecting-window offices recorded the highest adjusted RH (70.56%). Although unadjusted findings suggested window-related differences in carbon dioxide, the final regression indicated that the number of windows (B = -9.24, p = 0.041), rather than typology, was the stronger predictor. Overall, the study demonstrates that window geometry is an important determinant of pollutant dilution and moisture control in naturally ventilated tropical office buildings, and that performance-based window selection represents a low-cost passive strategy capable of improving indoor environmental quality and supporting energy efficiency.
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