Assessing the Effects of Building Spatial Layout on Window to Wall Ratio in Temperate Dry Climate of Nigeria

The window-to-wall ratio (WWR) is very vital in achieving optimum Passive Indoor Thermal and Visual Comfort (PITVC) in buildings, particularly in tropical countries like Nigeria. Researchers have diverse views on the proper WWR for optimum PITVC in buildings. Some researchers have found out that buildings with WWR above 20% do not provide comfort temperature. Others have recommended 25% as the best WWR in the tropics, while ASHRAE 90.1 (2007) recommended a value of 24% as the optimum value for daylight and natural ventilation, and considered value below that as poor, and a value above 30% overheated. The International Energy Conservation Code recommends a different value of 30%. These and many more have not considered the effects of building spatial layout on WWR which this research is aimed at doing that in the temperate dry climate of Nigeria. It was achieved by using three (3) different building spatial layout (single-banked, double-banked, and open planned) and for each a range of values of WWR was used to determine the difference in daylight autonomy (DA), useful daylight illuminance (UDI100-3000), spatial daylight autonomy (SDA), operative temperature (OT) and relative humidity (RH). Data was collected from simulation of the prototype single-banked, double-banked, and open planned office buildings, using google Sketch-Up 2017 and open-studio simulation tool which was done on the hypothetical sites devoid of surrounding buildings and trees, in Jalingo, Minna, and Zaria. Data generated were then analysed using ANOVA, bar charts, column charts, graphs, and tables with significance threshold of 0.05. The findings revealed that, the best WWR are 20% and  15% for visual and thermal comfort in single-banked office buildings, 45% and 15% for double-banked and 30% and  26.5% for open-planned office buildings respectively. When the values of daylight metrics and thermal comfort indicators were ranked together, 20% was found to be the most compromised value for single-banked, 45% for the double-banked and 30% for the open-planned office buildings. One-way MANOVA was used and a statistically significant difference was obtained, F (30, 210) = 8.634, p < .0000; Pillai’s Λ = 2.761, partial η2 = .552 for single-banked, F (20, 296) = 18.828, p < .0000; Pillai’s Λ = 2.240, partial η2 = .560 for double-banked and F (20, 136) = 10.187, p < .0000; Pillai’s Λ = 2.399, partial η2 = .600 for open-planned office buildings. The implication of this study is that the three (3) building spatial layout must have different framework to achieve PITVC in temperate dry climate of Nigeria.