Shade: A Hot Climate Design Challenge for the 21st Century

David Baggs, CEO and Technical Director

As humans in a hot climate, we instinctively seek shade when subjected to the hot sun. In our early buildings and even in the adoption of traditional Middle Eastern Dishdasha and Abaya garments or the traditional tropical ventilated double roof is the instinctive acknowledgement that shade drives comfort in hot climates.

Hot climates include both hot wet climates like the Middle East, tropical and sub-tropical areas such as India, Asia and , Australia, Southern USA and South America, but also desert climates like Australia, USA and Africa.

plane.pngFigure 1: When it's hot you need shade.

Early desert buildings limited window openings and created deep set windows and occupied rooms within heavy mass walls. Tropical buildings in having to cope with large volumes of water instinctively added shade by including overhangs to keep out the rain. This was all driven by people's experiences in trying to reproduce environmental conditions that created comfort.

However with adoption of minimalism by modern architecture and the rollout of minimalist, predominantly glass commercial buildings globally, design strategies have been introduced into hot climates that are not appropriate. Why have we let this occur?

som bank.pngFigure 2: Few modern buildings recognise the short comings of glass as a radiant barrier and the benefits of well insulated walls as dramatically as this SOM Bank Building in Jeddah KSA.

Part of the answer is due to the perception that new glass technology is able to reduce heat to manageable proportions. Another part is the perception that 'smart glass' allows 'affordable' air conditioning solutions. The reality of the situation is quite different to the perception.

 

 

 

 

 

 

 

grosvenor square.pngFigure 3: Grosvenor Square Building Sydney: Architect Harry Seidler - one of the few Modern School architects who adequately and consistently considered shading.

In the peak of summer, in a hot climate typically the suns rays exert 800-1000Watts per square metre on both people and buildings; even in winter in such climates it is typically 500-800Watts per square metre under a clear sky. This equates in summer to a total heat load equivalent to a one bar radiator for every square metre of roof.

The reason this is important is that no matter how good  even double pane insulated glass is at preventing heat from the day being conducted through the façade of a building, solar radiation is a very significant additional load, that even the very best of reflective and selective glasses cannot completely stop.

While the inset figures are from temperatures taken by me over a period of time for a new office building in Jebel Ali in Dubai, the same climatic conditions can be found in many locations around the world.

The Building has a glass façade and unshaded high performance, reflective, double pane insulated glass, tinted in some areas and clear in others. Typically the air temperature inside is invariably 21 degrees. If you consider the figures, you will notice that even in winter when the sun is on the building's south face at 9.00am in the morning the temperature radiating from the inside pane of glass absorbed by the glass is 33 degrees! In summer at midday inside the clear glass it rises up to over 37 degrees.

jebel ali.pngTable 1: External and Internal Glass and Air Temperatures of Unshaded Office Building - Jebel Ali Dubai.

Imagine yourself sitting at a desk near those windows, even though the air conditioning is a chilly 21 degrees, the whole wall next to you is like a huge radiator at 37 degrees- so even though the air conditioner is working hard and from the room temperature it appears that everyone would be comfortable- you will be sweating and hot because the half of you facing the window is sitting in front of radiator. Your body gets confusing signals, you start sweating which in combination with the cold air temperature makes you feel more comfortable - but even if your body is comfortable enough not to move away from the glass, it is in a constant state of stress and over time this may affect your immune system, lead to a feeling of exhaustion and possibly even illness.

Heat loads on opaque elements in walls are more easily managed with insulation. A relatively small amount of insulation is sufficient to achieve this effect. 6 cm of polystyrene will reduce the overall heat transfer coefficient through a concrete wall from 3.0 W/m²oC down to 0.5 W/m²oC, but glass is much harder.

The thing is, with windows, the air conditioning system still has to deal with both the heat that does conduct through the glass and the direct solar rays absorbed by the glass and reradiated from the inside surface of the glass.

The whole issue of global warming generated in large part by the use of energy and made much worse in recent years by the dramatic rise in air conditioning  means we need to reconsider the way we think about how we use air conditioning. We need to think about it as a means of last resort to stay comfortable in a difficult climate and use every other means at our disposal to stay comfortable without expending energy.

The first, most important thing we should do before even designing the air conditioning plant is do everything we can to design the building to use the least amount of energy possible. Using passive means and to cut heat loads to the absolute minimum and then sizing the air conditioning plant to suit.

The first and most important thing to consider in tandem to reduce building heat loads is orientation and shading. Orientation because if we align our buildings in accordance with the true north/south, east/west axes, we also align the building with the symmetrical path of the sun throughout the year and make it easier and more cost effective to design simple fixed shading devices for south and north faces.

In the Middle East because of the way the sun travels from north to south, summer to winter at these latitudes, the east and west faces are best shaded with moveable shades to maximise efficiency- however the first skyscraper in Dubai - the Dubai World Trade Centre Tower, although the appearance is not 'fashionable' now, is proof that fixed shading can be designed to work well on all aspects if one is prepare to investigate all options. Interestingly - it also derives a strong Arab feel to the tower, something unfortunately missing from most modern Arab skyscrapers.

dubai world trade.pngEven though the north and south shading can be fixed, optimum shading for each elevation is not the same. On the south elevation in mid winter the sun is at 45degrees to the glass so fixed horizontal shading needs to be as wide as the distance between the shades e.g., a 1metre wide shade every 1 metre or a continuous mesh or Arabic screen, whereas on the north in summer, only very narrow horizontal shades of e.g. 10cm every metre combined with regular deep vertical shading blades is needed. In other climates the operable vertical or operable shades on the east and west work well and only small horizontal projections are need on the sun facing northern or southern faces (depending on which hemisphere the building is in southern  or northern respectively).

Figure 4: Close shading over Dubai World Trade Centre Tower.

There are some very sophisticated sunscreen design strategies that exist around the globe and the need for solar shading does not have to mean all buildings will look the same. It just means there is a completely different aesthetic to explore and one that is already being explored by some local architects. One such innovative company is Ahmed Al Ali's award winning Dubai-based X Architects with many examples of their work exhibiting a keen understanding of the need for shade and creative, traditionally rooted shade solutions evident in their designs.

 

 

shopping centre.pngFigure 5: Proposed Shaded Shopping Centre Ahmed Al Ali- X Architects.

The new Abu Dhabi Urban Planning Council's Development Regulations Code  recognises the importance of external shade and is requiring external building shading relative to the building aspect with 'percentage shaded' specifications for each aspect.

The challenge this throws down to architects hereafter is how to refashion the image of both skyscrapers and other buildings, to integrate external shading within the aesthetic and technical challenges of high rise and the design preconceptions that while widespread must go the way of the dodo if we are not to!.

While visionary architects like Malaysian borne, London based Ken Yeang in buildings like his Malaysian 'Fusionopolis' (it will be Singapore's most eco-friendly building) have been working on this conversion for years, the rest of the profession and building owners now need to come to terms with re-creating and re-interpretting the architecture of appropriately shaded modern buildings.

 

ken yeang singapore.pngFigure 7: Ken Yeang Fusionopolis, Singapore