Impact of solar radiation on westerly exposed facades of residential buildings in Dhaka

Abstract

In tropical climates, building orientation and materials used in the building envelope, dictate the Solar Heat Gain factor of the building. In both planned and unplanned morphological development in Dhaka city, unavoidable westerly oriented residential buildings, which are often the only exposed side, is a common phenomenon, due to site limitations. Published sources show that building energy consumption, in a typical planned residential area of Dhaka, increases 5.1% in its share of cooling energy consumption, for every 1°C increase in temperature. Given such a scenario, materials, and their use on building envelope, is a very important design consideration, in controlling overall solar heat gain during the overheated periods, which in turn can save energy used for comfort cooling. The main purpose of this investigation was to determine the impact of solar radiation on the building orientation with the west and the use of different materials and their proportions on the westerly envelop of residential buildings.

This thesis investigates a set of sample buildings of Dhanmondi, a typical planned residential area of Dhaka, to understand common design practices, construction materials used on westerly facades, along with their ratio/proportions on the façade, and occupant behaviour and consumption practices within these spaces. The study used field surveys, questionnaires, and interviews to set the basis for simulation models. The change in annual electrical energy demand, for comfort cooling is then simulated, using BEM software, for varying building orientations, with westerly exposed facades, composed of different materials and proportions.

The simulation results reveal a clear relationship between annual electrical energy demand for cooling and building orientation to the west. It also showed that an incremental increase in the ratio/proportion of the glazing surface to a solid wall increases the annual demand for cooling load. Analysis done on two years of monthly electrical bill data of the sample buildings presented a similar pattern.