Analyzing sunlight duration and optimum shading using a sky map

A method of predicting the sunlight duration on windows in a densely packed building environment is presented. This method is based on dividing the hemispherical sky into small patches of 5°×5° and determining (using long-term climatic data) the probable sunlight duration with the sun locating in each sky patch. Hence, a sky map is constructed which gives the sunlight duration from every patch of the sky. A graphical tool and a spreadsheet calculation method have also been developed for designing external shading and calculation of probable sunlight duration. Optimum external shading configurations are suggested for different façade orientations of an isolated building in Hong Kong.