Investigating the functionality of permanent sun shading devices on high rise buildings of Addis Ababa using custom-made Heliodon

Abstract

The application of shading devices on buildings goes far back in history and it is being a necessary design element in the modern age as a method of achieving certain aspects of sustainability in buildings. These design features are essential elements in a step forward toward sustainable buildings. In the current state of the use of shading elements, particularly external permanent devices are recurring elements in the modern high-rise building of Addis Ababa. In addition to its fundamental purpose of providing shading against undesired solar exposure the elements also provide an esthetic quality to the general appearance. This paper investigates the effectiveness of these devices in terms of shading capability during overheated seasons. The overheated season is determined by identifying periods of the year exceeding a temperature threshold of 24 ⁰c for 2% or more time of the month. To conduct this investigation, a custom-made heliodon which is a device that can simulate the position of the sun in terms of azimuth and altitude on a particular location throughout the year is developed and used. The design basis is a conceptually clear model of heliodon first developed by Robert Lechner which intern is inspired by a geo-centric view of solar geometry. As such the custom-made heliodon with a 1:40 scaled model of selected high-rise buildings’ shading elements is used to determine the shaded fraction cast on the window glazing surface. Among various shading devices selected for this analysis, a horizontal louver on a vertical plane performs the best with 90% average shading. The lowers shading performance was recorded by vertical fins facing southeast at 45% shading. Combined shading system of vertical overhang with horizontal louvers sowed above 70% of shading in their respective orientations. A result verification conducted using a mean absolute percent error resulted in a 13% error margin. A computer simulation result was used as an accepted value to compare the results against. Finally, It is recommended that a thorough understanding of solar geometry be established while designing shading devices. Also, solar analysis using tools such as heliodons, solar charts, or computer simulation be conducted early in the design phase as these devices can play a crucial role in a stape towards sustainable architecture.