Sun , shade and natural daylight in South African town planning , with emphasis on Pretoria

A bioclimatic analysis of different South African towns and cities indicates that, if the correct mix of passive design principles is used, they all have a significant passive design potential. Of all such measures, solar protection and shading is the single most important passive design measure to reduce energy usage and to improve internal comfort for buildings in all South African climatic regions. The correct design of public open spaces and streets facilitates, to a great extent, energy-efficient buildings, whilst at the same time providing functional and comfortable urban open spaces and streets. 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. The aim of this article is to investigate the effect of climate zones on passive design potential, of which shading design is an integral part, using Pretoria as a case study. This includes the effect of street width, building height, street layout, orientation, and the amount of sunlight available for trees and plants in the urban environment. The Spatial Planning and Land Management Act (2013), City of Tshwane Land Use Management By-law (2016) and the Tshwane Town-Planning Scheme 2008 (Revised 2014) were used as regulatory framework. To support the research, an Early Design Phase (EDP) experimental research platform was used to investigate the amount of sunlight on building facades with different orientations. This method enables the calculation of shading angles where there is a balance between the hot periods (requiring cooling) and cool periods (requiring heating) from the urban and building perspective. This has been achieved by means of the development of analytical software that uses weather files as one of the inputs to calculate critical solar angles. Over and above the calculation of current building solar protection angles, this method also facilitates the calculation of the increase in solar protection that will be required with climate change such as with the expected A2 climate change scenario (business-as-usual scenario) for South Africa. To support the EDP analysis, detailed simulations were also undertaken by means of Ecotect v5.60.


BACKGROUND
According to UN-Habitat (2014: 1), there are five principles for sustainable neighbourhood planning: • Adequate space for streets and an efficient street network.• High density.
From 2007 to 2009, the recorded building plans passed by South African municipalities for residential buildings, non-residential buildings and additions totalled 61,939,720 m², with a value of R 231 250 619 000 or approximately US $33,8 billion (using January 2011 exchange rates).These amounts indicate the extent of formal growth in the South African built environment, and the increasing contribution thereof to building activity on the African continent (Laubscher, 2011: 68).A study of the various regulations below indicates that there are hardly any or limited statutory regulations that can direct built environment development towards sustainability ideals.Furthermore, there is almost no integration between the town planning side and the national building regulations.
Three levels of design intervention can be distinguished, namely building, urban, and regional.Previous research indicates that, in a hot country such as South Africa, the most important factors at building level are building orientation, solar shading and penetration at appropriate times (Conradie, 2016: 38).The general principle is that the sun should help heat buildings in winter and, therefore, be allowed to penetrate the building at this time.However, in summer, the building and especially the windows should be protected against direct solar radiation.The appropriate use of glass is closely related to the latter.Other factors such as building shape, building depth, insulation, opening areas, air tightness and correct use of mechanical systems are also important.It is also beneficial to use cool roofs and surfaces in their various forms such as green, blue and reflective cool roofs (typically white roofs).At urban and regional level, the use of plants and street trees (Stoffberg, Van Rooyen, Van der Linde & Groeneveld, 2010: 9) is a good method to reduce the UHI, due to a combination of shade and evaporative cooling (Stoffberg et al., 2010: 9).   1 See Figure 1 for the various heating and cooling zones.
2 Weather files with an A2 climate change scenario as defined by the IPCC (2000: 3-5) were used to calculate these values.

INTRODUCTION
At about the same time that two prominent medieval European cities, Paris and Barcelona, were drastically transformed and improved, Pretoria was founded in 1855 by Marthinus Pretorius, who named the town after his father Andries Pretorius (Figure 5).Pretoria was surveyed in its formal grid pattern by its first landdrost, From an analysis of the original town planning of Pretoria (Figure 5), it is clear that the development of the city was directly influenced by various geographic features and historic events.The following observations are made with regard to Pretoria:

EXPOSURE TO SOLAR RADIATION
In an analysis of nearly 200 solar design tools, Jakica (2018: 1296-1298) extensively examined the numerous software features regarding accuracy, complexity, scale, computation speed, representation, and building design process integration in about 50    Source: Author 0° (north).The elevation is expressed in degrees from the horizon to vertical (0° to 90°).This facilitates the study of the annual temperature and radiation distributions and supports advanced early design-phase analysis to determine the times when solar protection and shading would be necessary.Four temperature Unlike the diagrams suggested by Mazria (1979: 267-308) and the Climate Consultant 6.0 software, this research platform supports a bearing of any angle including due south.

The effect of building height and street width on solar insolation and natural daylight
To study the effect of building height and street width on the availability of sunlight and natural daylight in the Pretoria CBD, a simulation model was defined by means of the Ecotect v5.60 energy simulation software.For this simulation, the following assumtions were made:  The overshadowed building has hardly any direct sunlight, when it is most needed.The building on the southern side of the site is also somewhat affected.

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• The overshadowed building is a fixed height of 38 m.
Table 5 shows that an increased height in the overshadowing building has a dramatic effect on the availability of sunlight (insolation) in winter.This is the time when sunlight is most needed.The availability of natural daylight is not affected that much as a standard Commission Internationale de l'Eclairage (CIE, 2002: 6-7) overcast sky was assumed and used in the simulations.During summer, the effect is not that drastic both with regard to insolation and natural daylight, as the solar elevation angles are high above the horizon and the overshadowing building does not have a big effect.
If a multi-storey building is to be completely lit by daylight, then there are limits on its overall plan depth.If a day lit room is too deep, the rear will look gloomy compared to the brightly lit area near the windows.If a day lit room is lit by windows in one wall only, the depth of the room L should not exceed the limiting value given by (CIBSE LG10, 2014: 26): Where: L is the room depth, W is the room width,    • As before, a street total street width of 25 m is assumed.This includes 2.5 m sidewalks on both sides and a 20 m vehicular lane width.• In each case, the insolation and overshadowing of the long facade of building 2 on the site was studied (the southernmost potentially disadvantaged building).

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On summer solstice (21 December), the sun rises at an azimuth of 116.62° and sets at 243.35°.At noon, the sun reaches an elevation of 87.7° and the length of day is 13h45.
On winter solstice (20 June), the sun rises at an azimuth of 64.24° and sets at 295.76°.At noon, the sun reaches an elevation of 40.84° and the length of day is only 10h32 (Figure 8).These solar angles have a significant effect on the overshadowing characteristics of the southernmost building, especially in winter.The winter solstice noon angle roughly corresponds to a building height of between 20 m and 26 m in the specific case illustrated in Figure 11 and Table 5.

The potential effect that a Form Based Code (FBC) might have on solar insolation and natural daylight
To illustrate the potential effect that an FBC approach might have in the Pretoria CBD, a simple illustrative simulation was undertaken by means of the Ecotect v5.60 energy simulation software for only model A with building orientations east-west as before.For this simulation, the following assumptions were made: • The same weather file was used for all studies in this article (including the bioclimatic analysis), i.e.Pretoria Forum generated by Meteonorm v7.2.4.• In all cases, simulations were done for the winter solstice (20 June) and for the summer solstice (21 December) (Figure 12).• A standard Pretoria CBD streetblock of 226.69 m x 151.13 m was used.
78 5 Average insolation hours for only building 2.
• The actual orientation of the Pretoria CBD street blocks was used, i.e. 4.24° west of north.• Building 1 is in the same location as before.However, the building height has been reduced to 8 storeys.• Building 2 is in the same location as before.However, the building height has been increased to almost 13 storeys.This height has been calculated by means of the winter solstice angle of Pretoria (40.84°) taken from a point across the street on the southern side of building 2 in such a way that no overshadowing takes place at this time (Table 7).• Building 3 was kept at the original height; it moved north by 20 m to reduce overshadowing of building 2. • As before, a street total street width of 25 m is assumed.However, the walkways are now much wider to make the city more walkable, as the pedestrians now take precedence over vehicles and the vehicular lanes are narrower with less prominence given to parking (Nel, 2016: 261).• A large green space has been opened, inspired by the Barcelona manzana, between buildings 1 and 3 to facilitate the introduction of compatible mixed uses such as bistros, restaurants, retail, offices, and small 'home industries'.
The area is sufficiently large that vegetation can grow successfully to provide shade in summer and to reduce the effect of urban heat islands.This effectively split the very large Pretoria street block into two and will provide a better connection to the streets south of this block if an arcade is introduced underneath building 2. • At the street intersections, the corners are chamfered at 45° to reduce the effect of the street canyon and to provide better visibility to pedestrians and traffic.
In each case, the insolation and overshadowing of the long facade of building 2 on the site was studied (the southernmost potentially disadvantaged building).See Table 7.  8 Shading characteristics for buildings 1, 2 and 3.

Bioclimatic analysis
In addition to the other simulations discussed earlier, a bioclimatic analysis was used to quantify the indicates when shading should be introduced.This corresponds to the Hot(red) category in Figure 8.
Bioclimatic design is used to determine the best set of passive design strategies for a building that uses natural energy sources and, therefore, significantly reduces energy use (Visitsak & Haberl, 2004: 1-11).This approach was already developed in 1963 by Olgyay (2015: 14-31) to ensure the best use of the specific climate and comfort in buildings.14).The program then calculates how many hours fall within the specific strategy zones.This is based on  Source: Author the theoretical work of Givoni and Milne (1979: 96-113) and makes it possible to determine which passive design strategies are most appropriate to design a comfortable building.Exactly the same weather file used elsewhere in this article was used for this analysis.

A: Horizontal overhang (fixed)
This type of overhang is mostly suitable for altitude-/elevation-(sun is far above the horizon) dominated solar angles, typically on northern (or near northern) facades.It can take various forms such as illustrated in Figures 15A to 15E.This could also be in the form of a projecting awning or sunblind.

B: Fixed vertical screen
This configuration is a variation of A and is intended to exclude the lower rays of the sun, thereby reducing the glare problem.

C: Side fin/vertical projection (fixed)
The side fin used on its own is suitable for use on facades where the solar altitude/elevation is mostly azimuth dominated, i.e. low solar angles above the horizon.This option is often combined with A for facades

Solar protection at building scale
At least 12 different generic shading devices can be identified at building scale (Figure 15).Generally speaking, shading types that exclude the sun externally during the overheated period and allow it in during the cold period are more efficient.By contrast, although fixed screens are very efficient, they have the disadvantage that they exclude the sun, even during the cold periods.Hence, that are not due north and where there is a mix of altitude-/elevationand azimuth-dominated solar angles that need to be excluded.

D: Light shelf (fixed)
This is another variation of A and is used to improve the natural light penetration in a space by means of a reflecting light shelf.

E: Horizontal louvres (fixed or moveable)
This is a variation of A and, if it is moveable, it is more flexible than A. It is typically used with altitude-/elevation-dominated solar angles.They have the advantage to permit air circulation near the facade.Slanted louvres give better protection than vertical ones.

F: Vertical louvres (fixed/moveable)
This protection device is found in different forms.In its simplest form, it could be a fixed vertical screen some distance away from the building facade.In a more complex form, it could consist of multiple louvres set right in front of the window or some distance away from the facade.The most sophisticated variation would be a moveable system with or without computer control.

G: Integral blinds
In this system, blinds are built into a double glass system.This has some advantages such as the protection of the blind.These systems are normally moveable.

H: Special glass such as heat absorbing, reflective and photochromic
This is the weakest type of shading device, as it depends on the treatment of the glass and can ultimately not avoid heat gains in the interior.

I: Vertical external screen
There are many types of this screen.
In its simplest form, it could be a fixed fine woven metal mesh.
More complex systems consist of special screens that can be opened and closed when desired.

J: External louvres, insulated louvres, louvered blind and vertical roller blind
These types are mentioned by CIBSE (2014: 39) and there are many variations with varying degrees of durability.Some researchers even suggested the integration of screens with flexible photovoltaics (Sampatakos, 2014: 71-110).

K: Internal screen, louvre drapes, blinds or curtains
This family of solar protection devices are not that efficient to reduce heat in a space, as it is not excluding the solar radiation from the outside.This causes the gradual build-up of heat in the space, due to the hothouse effect.However, it is useful as a means to control solar glare with low solar angles in the early morning and late afternoon.Ideally, these types of devices should be used in conjunction with wellengineered external solar protection devices.This type of screening could be venetian blinds, vertical louvered retractable blinds, fabric roller blind and fabric curtains.with large tree crowns.The average mrt T in a street with a 54% surface of tree crowns was found to be 4.5 °C lower than in a street without trees.(Van Hove et al., 2014: 66).

L: Double-skin facade
Van Hove et al. (2014: 24) also found significant correlations (p < 0.05) for both the surface temperature and the air temperature for the fraction of built surface, the fraction of paved surface, and the fraction of urban vegetation.Urban vegetation cools the environment through transpiration and shade.However, this means that enough water must be present.
On summer days, it can be 3 °C cooler in a small park than in the surrounding built area.However, the influence of the Park Cool Island effect on the surrounding built environment is unfortunately minimal.
There is also a strong positive psychological effect of green gardens on how pedestrians perceive temperature.Visible green elements at different heights such as low shrubs, hedges, green facades and tree canopies make the heat more bearable for people, and they also appreciate such streets more from an aesthetic point of view.
Vegetation and trees are, therefore, very useful measures to reduce the Urban Heat Island (UHI) Effect.
Trees not only provide shade, but they are also a very effective carbon sink.A carbon sink is a process or mechanism that removes Carbon Dioxide (CO 2 ), one of the greenhouse gasses, out of the atmosphere.Carbon is sequestrated in the trees' wood at different rates and quantities.This is dependant on factors such as growth rate, specie, size of the full-grown tree and expected life.(Stoffberg et al., 2010: 9).Many international studies confirm these advantages.For example, Kuittinen, Moinel and Adalgeirsdottir (2016: 623-632) studied the urban ecosystems of the Finish city Espoo.They studied seven housing complexes and found that the sequestration or uptake of the CO 2 by growing plants and the uptake of soil organic carbon varies considerably.The sequestration as a percentage of all releases varied from 1.2% to a more significant 11.9%.The best values were measured at a stand-alone house and the worst at an apartment block.  .It was estimated that tree planting would lead to an estimated 200 492 ton equivalent CO 2 reduction and that 54 630 ton carbon would be sequestrated.
The research was based on three indigeneous species, i.e.Combretum erythrophyllum (Vaderlandswilg), Searsia lancea (Karee), and Searsia pendulina (Witkaree).This base information was used to estimate the carbon sequestration of the other tree species such as Acacia caffra en Galpinia transvaalica.

Cool roofs and surfaces
Many roofs and impervious urban paved areas in South Africa have a dark colour and reach high temperatures on warm sunny days.These surfaces store and release a large amount of energy into the atmosphere.Hot surfaces also accelerate the deterioration of the materials.Buildings with inferior or inadequate roof insulation increase the amount of cooling energy required and have a negative impact on the comfort of building users.Current research trends in the field focus on the development of highly reflective pavements and permeable pavements that use evaporative cooling of water that could penetrate the surface (Icaza, 2017: 78).
The spatial variation in surface temperature is related to the average Sky View Factor (SVF) and surface albedo in an area.Neighbourhoods with a larger average SVF and a greater surface albedo have a lower surface temperature.A possible explanation is that a higher SVF and greater surface albedo mean that less solar radiation is absorbed, so that surfaces heat up less during the day (Van Hove et al., 2014: 28).
It is currently possible to create a cool roof with advanced materials that are not white, although white cool roofs are quite common.This is achieved by substantially increasing the reflectance of the surface treatment paint.

CONCLUSIONS
South Africa's current climate is predominantly arid, with 70.9% of the area falling in the Köppen-Geiger categories BSh, BSk, BWh en BWk (Conradie, 2012: 181-195).However, a bioclimatic analysis indicates that there is a significant amount of passive design potential.
To realise this passive design potential effectively in the highdensity central city developments, a specific site cannot be seen in isolation.Each development will have to be seen in relation to the neighbouring site and buildings, in order to avoid negative effects such as severe overshadowing that reduces the potential to benefit from solar gains when required and the use of renewable energy.
Street and public space vegetation also requires a sufficient amount of sunlight to grow.It is recommended that municipalities such as CoT investigate and gradually move to FBC as it might be a better regulatory approach than the current zoning-based codes.
FBC has a significant potential to improve sustainability in the general urban areas of South African cities.This should be investigated.
East-west (long axis of building) building orientations are significantly better for the use of solar potential and natural daylight.North-south building orientations are not ideal.
The high rise part of a high-rise density development can be closer to the northern edge of the site due to the Pretoria solar angle geometry.This reduces the possibility of overshadowing in street blocks directly south of the high-rise building.
It is recommended that the winter solstice noon elevation angle be used as the threshold angle to limit overshadowing and to ensure adequate natural daylight.It is a reliable conservative method, as it will automatically take account of the solar angles in other South African cities that are situated at different latitudes.In the case of Pretoria, it automatically leads to a street width, building height factor of 1.
It is recommended that specific building-facade designs first consider the design of solar protection measures such as horizontal overhangs and then the provision of adequate natural daylight as natural daylight is more diffuse and is not affected as much as insolation with an increased height of buildings.The general rule is shading in summer and solar penetration in winter.
Climate change will have a significant impact on South African cities.
Fortunately, there is a wide range of measures that can be used at building, suburban and urban level to reduce the urban heat island effect such as cool surfaces, green roofs and the extensive use of trees and vegetation.The low population density of many South African cities is cause for concern, because it gives rise to increased urban heat islands, and transport costs become very expensive, due to the long travelling distances and an increased carbon footprint.New cities should, therefore, be planned in a far more compact manner, and existing cities should gradually be increased in density.
The above simulations clearly indicate that densification should be properly planned to ensure the full realisation of the passive design potential of a specific city.

Figure 1 :
Figure 1: Combined heating and cooling low, medium and high (LMH) zone map with summer and winter humidity lines for South Africa (Conradie, Van Reenen & Bole, 2015: 101-117).The overlaid percentages indicate the bioclimatic calculated passive design potential of various cities in South Africa.Source: Author 7 8

Figure 3 :
Figure 3: Three-sided manzanas with a central public green space as originally drawn by Cerda.This is one of the originally proposed detailed layouts for the square street blocks shown in Figure 2. The large courtyards allowed adequate ventilation, sunlight and natural daylight.They provided a pleasant living environment for the inhabitants of the 20 apartments.Source: Doerr, 2014: online

Figure 5 :Figure 6 :
Figure 5: Old plan of Pretoria (1878), showing the Roman grid-type layout and natural features such as rivers, mountains and koppies that influenced future development.Note the inaccurate north indication in the drawing.Source: SA HISTORY, 2018

Figure 6
Figure6details some of the current morphologies and building typologies found in the city.The street orientations vary significantly, from ideal to very bad from the point of view of passive design and energy efficiency.Depending on the size of

Figure 8
Figure 8 is an analytical graphical screen that displays the annual temperature/radiation combinations with solar azimuth on the horizontal axis and elevation above the horizon on the vertical axis.The azimuth is expressed in degrees clockwise from

Figure 8 :
Figure 8: Annual solar charts for central Pretoria that indicate the temperature radiation profile for 0° (top left), 90° (top right), 180° (bottom right) and 270° (bottom left) orientations (all angles are measured clockwise from north).The horizontal axis is the solar azimuth (horizontal angle in clockwise degrees from north) and the vertical axis the solar elevation in degrees above the horizon.Source: Author

Figure 9 :Figure 10 :
Figure 9: Insolation calculation for 21 June (winter solstice) with an overshadowing building of 38 m height.Source: Author

wH
is the window head height above floor level, and b R is the average reflectance of surfaces in the rear half of the room (away from the window).If L exceeds this value, the rear half of the room will tend to look gloomy and supplementary electric lighting may be required.Street trees are one of the most effective measures to reduce local outside temperature with the combination of shade and evaporatative cooling.Van Hove, Blocken, Van den Dobbelsteen, Spit & Bosch (2014: 52-53) opined that streets should be twice as wide as the building height.From the results of the simulations illustrated in Figure11, this appears over-conservative.Van Hove et al.  (2014: 52-53)  wanted to ensure that there is good natural ventilation and to avoid the urban canyon effect.Parks at urban and regional level, especially during heatwaves, are very important.Parks are like cool islands within a city.Laying out more parks with different microclimates provides urban inhabitants with a choice as to where they feel comfortable.Parks can simultaneously act as a water buffer during extreme rainfall.

Figure 11 :
Figure 11: Elevation angles used to study the effect on solar insolation (sunlight exposure) and availability of natural daylight in the CBD of Pretoria with different overshadowing building heights.A total street width of 25 m was used.The overshadowing building is on the northern side and the overshadowed building on the southern side.The actual orientation of the CBD of Pretoria was used in the calculation of solar insolation and natural daylight.

Table 1 :
Quantified benefit of solar protection benefit for various cities and towns in various climatic regions with and without climate change

Table 2 :
Characteristics of the Pretoria urban morphologies as illustrated in Figure6(the densities vary drastically)

urban morphologies found in the City of Tshwane area
Source: Author, based on 2011 Census the individual erf, plot or stand, this could have a significant impact on the energy use of the facilities and the opportunity to use passive design techniques.The characteristics of the urban morphologies illustrated in Figure6are summarized in Table2.

Table 3 :
Differences between FBC and conventional zoning approachesDistinct character and mixture of compatible uses.Note the figure eight patterns in Figure8.These are called the analemmas and are essentially the effect of the difference between apparent and mean time (equation of time).In other words, it is the difference between the hour angles of the true sun and the mean sun.Sometimes the true sun is ahead and sometimes behind the mean sun.This is caused by the earth's slightly elliptical orbit and the varying orbital speed that, in essence, follows Kepler's laws.Figure8is, therefore, expressed in mean sun time (clock time) to make it more accessible for direct civil use(Meeus, 2015: 183).Table4summarizes the theoretical maximum amount of hours' sunlight (solar radiation) that the four facades of a building would receive with different primary orientations in Pretoria, if no overshadowing takes place.

Table 4
illustrates the total amount of annual sunlight hours that will theoretically be available for the different facades of a rectangular building in Pretoria (Latitude 25.733°, Longitude 28.183°).This has been calculated by means of the EDP experimental platform that is able to accurately calculate the solar azimuth and elevation and combines it with a typical meteorological year weather file for Pretoria Forum weather station.If the main orientation is 0°, then Facade 1 would face due north.

Table 4 :
Theoretical maximum amount of sunlight exposure (hours per annum) available for the different facades of a rectangular building with different orientations in the CBD of Pretoria if no overshadowing is taking place

Table 5 :
Solar insolation and availability of natural daylight in the CBD of Pretoria with different overshadowing building heights

Table 6 :
Solar insolation and shading characteristics for building configurations A, B and C

Table 7 :
Solar insolation and shading characteristics for building configuration A using a FBC approach 787 Average insolation hours for only building 2.
Table 8 was calculated by means of the advanced Climate Consultant 6.0 software developed by Robin Liggett and Murray Milne of the UCLA Energy Design Tools Group, with technical support of Carlos Gomez and Don Leeper.The software makes it possible to overlay a weather file (8 760 hours) on an electronic version of the psychrometric chart illustrated below (Figure

Table 8 :
Quantified best set of bioclimatic design strategies for South African towns and cities

Table 8
Stoffberg et al. (2010: 9-14)estimated the carbon sequestration for street trees in Pretoria (CoT).In 2002, CoT formulated a strategy to plant 115 200 indigeneous street trees between 2002 and 2008.The author is not able to verify if this has actually materialized.The results of growth regression were used to estimate the carbon sequestration tempo of the different species of trees.These results were then used to estimate the total carbon sequestration for a 30-year period