Daylight simulation for sustainable urban office building design in Dhaka, Bangladesh: decision-making for internal blind configurations

In an urban site, daylight strategies increasingly depend on the availability of natural light, which is influenced largely by the immediate surroundings of the building, particularly the presence of natural and manmade obstructions. Under such conditions the latitude of the site and its regional climatic conditions, such as ambient outdoor daylight levels and sunshine probability are found to have diminished direct impacts on the interior daylight potential. In these highly specific urban environments created by built-up surroundings, no generalised way exists to describe or predict the luminous microclimate. However, simulation can be used as a design tool for sustainable daylight design. Using simulation programs, this paper examines the significant impact of surroundings on daylight probability on urban buildings. Daylight simulation was performed in this study by creating the virtual urban environment based on the information of a true site urban office building in Dhaka, Bangladesh, a tropical location, with predominantly overcast skies. The 3D models were first generated for computer simulation in the Ecotect program to calculate the amount of daylight incident on a generated grid point on the work-plane. These models were then exported to Radiance Synthetic Imaging software to generate realistic lighting levels and finally verified with DAYSIM simulation program for annual performance evaluation. The results show that daylight entering from different sides of the building is affected vastly by surroundings and this influences the indoor illuminance and luminance distribution. This paper also demonstrates a case of decision-making between two most popular configurations (vertical and horizontal) of internal blinds used in urban offices of Dhaka. The focus of the paper is to highlight the importance of daylight simulation in sustainable urban office building design, while at the same time gives a general methodology for decision-making regarding daylight design elements.