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Designing for South African Climate and Weather

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February 20th, 2013 by Alive2green Green Building

Designing for South African Climate and Weather

To design energy efficient buildings using the correct combination of passive design strategies such as insulation, thermal mass and natural ventilation it is necessary to understand the particular climate very well. To perform a quantified building performance analysis by means of simulation software a detailed set of quantified climatic data is required.

 

The climate of an area is the averaging effect of weather conditions that have prevailed there over a long period of time such as 30 years. Due to the fact that earlier researchers did not have computers and electronic databases to research the gradual changes in climate Wladimir Köppen and Rudolf Geiger inter alia regarded climate as constant and used all of the sparse climate information available to compile a single climatic map[1] (Rubel et al., 2010). Today we know that the climate is constantly changing over time due to a complex interaction of factors.

 

Climatic classification is an attempt to formalize the process of recognizing climatic similarity (Kruger, 2004). Some of the benefits of climatic classification are:

  • To indentify areas of influence of various climatic factors
  • To stimulate research to identify the controlling processes of climate
  • To inform an appropriate scientific response to building design

 

2 Climatic classification

2.1 The climate regions of South Africa

Low and Rebelo subdivided the seven vegetation biomes in South Africa into 68 vegetation types which consist of different concentrations of vegetation species. These types are mainly determined by climate, but sheltering, soil type, occurrence of veld fires, browsers such as goats and wild life, elevation and inclination and other minor factors also play a role. The boundaries for climatic regions were determined by making use of these vegetation types. Combinations of smaller vegetation type areas into larger regions that are easier to map and described from a climatic point of view, were made (Kruger, 2004).

 

Nine Savanna-type climatic regions have been identified, six Grassland-type regions, five Karoo-type regions, two Fynbos-type regions, one Forest-type region and one Desert-type region.

 

2.2 SANS 204-2

The SANS 204-2 (2008) standard recognizes six main climatic regions in South Africa. It is an attempt to introduce a quantified view of climate into the National Building Standards. If this classification is compared with more detailed research work it is clear that much refinement would be required to support designers within the built environment. The chapter about fenestration in said document provides a detailed description of the calculation of conductance and solar heat gain for glazing elements supported by extensive look-up tables and diagrams.

 

For each of the six climatic zones tables are provided that gives the solar exposure factors and coefficients (SHGC) for various overhang/ height (P/H) factors for eight main orientation sectors. The standard is useful for initial desktop calculations. It is clear from SANS 204-2 (2008) what the beneficial impact of fenestration design in combination with appropriate sun protection could be. This should be quantified with more detailed calculations preferably with simulation software once the designer has determined the sun protection devices that will be used.

 

Meteonorm files differ slightly from the CSIR classification. The reason is that the CSIR Köppen map is based on a very high resolution 1 km x 1 km grid using 20 years worth of monthly temperature and precipitation data ranging from 1985 to 2005. Although the Köppen map is only based on precipitation and temperature it is a convenient way to check the validity of weather files used in more detailed building performance simulations. The reason for this is that if a particular weather file's Köppen classification differs then it very likely used different data for precipitation and temperature.

 

The first three columns of Table 2 illustrate the SANS 204-2 climatic classification. The colours are as used in the SANS-204 norm. Columns four to six contains additional information. Column four contains the CSIR Köppen- Geiger classification that was derived from 20 years of monthly precipitation and temperature data on a 1 km x 1 km grid. The colours used here is identical to those used in the CSIR Köppen map. The formulae as described in detail by Kottek (2006) were used to calculate the classifications. It is clear that the SANS-204 classification is very coarse and an over simplification of the real situation. In the right hand columns some temperature graphs are shown that give an indication of the monthly and annual maximum, minimum and average temperature profiles.

 

To calculate or simulate the expected building performance by means of desktop, spreadsheet or advanced software such as EnergyPlus or Ecotect reliable weather files are required.

 

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Green Building Media is a South African media and events company that aims to educate South Africa about Green Building practices, methods, materials and green building technology.

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