Sun and shade

Abstract

South Africa is blessed with some of the best quality sunshine in the world but at the same time has some of the most intense solar radiation. There are therefore many exciting opportunities to utilize the sun to its full potential in the design of energy efficient and comfortable buildings. Previous chapters discussed various sun related aspects such as possible corrective actions in a very hot naturally ventilated office during the hottest summer in Pretoria (Conradie, 2016b), the optimisation of daylight in South Africa, the general weak thermal performance of fenestration (Conradie et al., 2015a), the use of glass in buildings (Conradie et al., 2015a), maximising use of the sun (Conradie, 2011) and passive design strategies (Conradie, 2013). Some of the articles were qualitative and others quantitative. There is a general paucity of information with regards the amount of incident solar radiation on the various building surfaces in the different climatic regions, cities and latitudes in South Africa. Bioclimatic and other analyses of the major cities indicated clearly that appropriate solar protection is the single most important measure in all climatic regions. Passive solar buildings aim to maintain interior thermal comfort throughout the sun's daily and annual cycles whilst reducing the requirement for active heating and cooling systems. This chapter continues on the basis of previous research, mentioned above, to quantify the energy benefits when various solar protection measures are applied to the different (east, north, west and south) and roof in all the climatic regions of South Africa. At the moment it is rather difficult to obtain such quantified information. The article also investigates the changes in solar protection, such as overhang sizes that will be required with an A2 scenario (business as usual) of climate change. An A2 climate change scenario as described by the Intergovernmental Panel on Climate Change (IPCC, 2000) is where the Representative CO2 Concentration Pathways (RCPs) are set to increase to 950 ppm, from a current basis of 400 ppm, by the year 2100 and even higher to 1 200 ppm after the year 2100. This RCP8.5 scenario corresponds to an energy increase of +8.5 W/m² by 2100. Insights are also provided how the overheated period can be determined when facades and especially windows need to be shaded. The article also touches on different types of solar radiation such as diffuse and direct and different types of shade such as the umbra, penumbra and antumbra. It continues with a discussion how the overhang sizes could be calculated to provide shading at the correct time of day and year.