The quantification of shading for the built environment in South Africa

Abstract

A bioclimatic analysis of South African towns and cities indicates that solar protection is the single most important passive design measure to reduce energy usage and to improve internal comfort for the built environment across all climatic regions. Passive solar buildings aim to maintain interior thermal comfort throughout the sun’s diurnal and annual cycles whilst reducing the requirement for active heating and cooling systems. There is a long history of methods to calculate the shading on buildings and a significant corpus of knowledge has been built up starting with purely graphical methods 60 years ago to recent parametric simulation with energy simulation software using weather files. This paper reviews the various shading calculation systems devised over the years. The effect of climate zones on the requirements of building shading design is also investigated. Different climate zones change the requirements of the size of horizontal overhangs on the northern façade (elevation dominated solar angles) and the periods when the eastern, western and southern facades (azimuth dominated solar angles) should be protected. An experimental research platform has been developed to support this investigation. This method enables the calculation of required shading angles where there is a balance between the hot periods (requiring cooling) and cool periods (requiring heating). Over and above the calculation of current solar angles this method also facilitates the calculation of the increase in overhang sizes that will be required with climate change such as with the expected A2 climate change scenario (business as usual scenario) for South Africa. This method is able to recommend different northern overhang sizes for cities and towns on the same latitude such as Upington, Kimberley and Bethlehem in South Africa. These three locations are on the same latitude but in totally different Köppen-Geiger climatic zones, i.e. respectively BWh, BSh and Cwb and altitudes. The current rigid geometric solar elevation angle approach does not take account of locations on the same latitude with different climatic regions and altitudes. This method proves that it is possible to analyse and quantify solar protection on building facades resulting in a rational balance between the hot and cold periods without using the current practice of extensive parametric simulation with energy simulation software. It is also able to distinguish between cities and towns on the same latitude but in totally different climatic regions.