THE SAHARAN SILVER ANT: Triangular shapes in architecture – facade manipulation, wind speed and natural convection

The Saharan Silver Ant (Cataglyphis bombycina) is one of the few animals that can survive high temperatures, even in the middle of the day. They usually leave their nest high noon when the temperature is around 47 degree celcius, searching for other animals, that succumbed to the tough desert conditions. Yet due to the threat of predators and the extreme high temperatures (Surface temperatures reach up to 70°C [2]) they are solely outside for around ten minutes, whereby they need to keep their own body temperature below the critical thermal maximum of 53,6 °C.
The ants have several features that adapt them to survive the heat. They have longer legs than other ants, which keeps them farther away from the hot ground. When running in full speed, they only use four of their six legs.
Furthermore when they travel through the desert they perpetually keep track of the sun, so they can easily navigate back to their colony.
Moreover the ants produce heat shock proteins, unlike other animals, before they leave their nest, not in direct response to the heat. This protein allows the organism to perform while exposed to high temperatures. If they did not produce it in anticipation of the extreme heat, they would die before the protein has its effect. [3]

Unique silver hair

saharan-silver-ant_head

Fig. 1: Head of ant covered with hair [6]

However the most interesting fact regarding these animals seems to be the distinctive silver hairs their body is covered with. (Fig. 1)
These hairs seemed to be one of the main reasons why the ants can stay out midday and search for their food, whereas other animals are victims to heat strokes.

 

 

 

microscope_hair_cut

Fig. 2: Triangular cross section [6]

An international team of researchers discovered that these hairs reflect a broad range of the electromagnetic spectrum to reflect sunlight and heat, which means they reflect not only visible but also near-infrared light.
Studies of the hair under microscopes revealed the unique shape of the hairs. (Fig. 2) They have a triangular cross section, which helps the light bounce of the surface of the hair and reflected to the next. Underneath the hair is an air gap, seperating the hair from the ant‘s body.

Studies under simulated sunlight showed that hairy ants are ten times more reflective than shaved ants and the temperature is around 5-10 degrees cooler than usual. (Fig. 3)

ant_heat_test

Fig. 3: Test under simulated sunlight [3]

As the hairs are highly emissive in the mid-infrared portion of the electromagnetic spectrum they are able to use thermal radiation to pass off excess heat.

Electron microscopy images of the hair show the form and surface of the hair. (Fig. 4 and 5) Two sides of the hair are corrugated with triangular patterns, while one side is flat. The hairs lie in the same orientation all over the body which results in gaps between the hair. [3]

The research team from Columbia University is currently working on adapting the results of the lessons learned for engineering purposes and take a look to create flat surfaces with an cluster of nanophotonic elements that have thermal radiative properties. [5]

However within the following analysis I want to focus rather little on reflective properties and more on the triangular shape and how this shape can be integrated into architecture.
I wanted to focus on facade manipulation and how triangular shapes can effect the thermal comfort in the building. In the following I will discuss the reflective properties, influence of wind speed and turbulences as well as natural convection in triangular shapes.

                                                                                                                                                                                                                                                                                                      1. ANALYSIS:

Reflective Properties

It seems like the reflectiveness of the hair is the main reason while the ants can stay cooler in the extreme temperatures of the desert. Although the researchers are working on reflective materials, one has to be careful in how it should be adapted in architecture, as too high reflections can lead to over heated surfaces on the ground or on adjacent facades. Especially in Morocco, the traditional architecture works with courtyards and narrow streets. Using a reflective material inside the courtyard would probably lead to an overheated ground and have not the desired effects of cooling down the building.
Nonetheless it might be possible to use reflective materials on surfaces that are not close to anything, for example the roof. However, to blend in with the material and architecture known in this region it is not useful to use sheated, reflective surfaces, but rather a granular material to mix into the production process of the clay bricks.

Wind speed

Triangular shapes have different properties when it comes to wind than for example rectangular shapes. In a simulated windtest (Fig. 6), using Autodesk Simulation 2015, one can see that the windspeed as well as the turbulences in the triangular shapes are higher than in the rectangular ones. The wind gets pressed into the shape which creates a tunnel effect and speeds up the wind going through. Although these effects are unwanted in colder regions (e.g. Sweden), where you try to protect yourself from the wind, to create thermal comfort, they are very useful in a hot-arid climate like Morocco. As the wind speed in this region is not very high, it is helpful to create something that can speed up the wind to support the natural ventilation in the building.

That being said, of course the simulation does not show the real life situation, however it does show how the wind speed can change through shape manipulation. Further simulations and experiments must be conducted to see the influence of heigth, width and depth of the triangular shapes and how it influences the flow not only into the building but out of the structure as well.

Natural Convection

The next focus point would be natural convection. As written in a paper called „A Comprehensive Review
of Natural Convection in Triangular Enclosures“ [6] the natural convection of an object is dependend on enclosure geometry, orientation and the thermal boundary. It is defined as a heat transfer with a natural fluid flow, without being generated by an external source. This usually happens because of density gradients, in this case temperature differences.

natural-convection

Fig. 7: Heated from below and heated from the side [6]

The triangular cross section is used for two reasons. On one hand it has a distinctive class of natural convection and embodies features of two types: Heated from below and heated from the side (Fig. 7), while also having the impact of corners on heat transfer and fluid flow. On the other hand it has practical reasons as it is used in buildings as roofing types, to achieve efficient ventilation.

However in this case I wanted not to use a big shape, like a roof, but rather smaller sized shapes, that can be included in the facade. Nonetheless I lack the proper equipment to actually conduct a study in natural convection in a building facade. However I do believe that the heat transfer from a triangular shape to maybe the next one could be beneficial when it comes to getting the warm air out of the building

 

2. RESEARCH RESULTS:

Facade Design

pictogram1

Fig. 8: Air flow diagram

Resulting from my previous investigation, I wanted to change the looks and properties of the traditional facade in Moroccan architecture. In most cases the facade is structured in two sections: Closed walls and openings (windows, doors). Concluding from my studies of wind an heat transfer I decided to place triangular shapes throughout the facade, to create natural ventilation and heat transfer (Fig. 8) Firstly I wanted to add openings on the top and at the bottom of rooms to create a natural air flow through the room (Fig. 9).

Secondly I created a vertical pattern as well, to not only show variety in size and shape, but also different aesthetics, as the triangular openings create a different look of the facade (Fig 10). I would suggest to have bigger openings where the wind is supposed to come in (bottom) and smaller openings in the top, to use them for natural convection and getting the heat out of the rooms.
The different sizes of the triangular pieces can create a new pattern in the facade but also adapt to the traditional patterns in Morocco. I imagine to work further on combining different shapes and sizes to create an overall triangular pattern.

facade_2

Fig. 9: horizontal facade manipulation (reference [8])

facade_1

Fig. 10: Horizontal and vertical facade manipulation (reference [9])

 

Production

bricks_vertical

Fig. 11: Closed brick (top), hollow brick (bottom

For the production of these shapes I was considering using clay to create these forms. Using clay would match the traditional building materials in Morocco.
It could also be made out of concrete, using a casting for the triangular shapes. There will be different sizes and shapes, but generally can be divided into two categories: Hollow and closed (Fig. 11).

 

Furthermore the triangular pattern can not only be used as the building structure (Fig.12), but also throughout the building as a cladding for walls and floors (Fig.13). These patterns would be created with the traditional tiling techniques seen in Morocco.

 

 

 

3. FURTHER INVESTIGATIONS:

Additionally to my studies on wind speed I was thinking of using the fact of creating turbulences to create evaporative cooling in buildings. If the surface and the material of the bricks could be changed in a way that they can collect or contain water, the effect of turbulences in these shapes can help to cool down the building with evaporative cooling.

Moreover I want to focus on not only creating triangular cross section but also other geometries, for example pyramids, to create a more elaborate facade pattern, that adapts to the traditional architecture and uses natural ventilation as well as natural convection.

The goal is, to create an overall cohesive structure that is both aesthetically and funcionally pleasing, using three dimesional elements as well as two dimensional tiling patterns.

                                                                                ______________________________________________________________________________________

Sources:

[1] http://www.trinitynewsdaily.com/theres-one-remarkable-ant-in-the-sahara-thats-coated-in-silver-hair/2614/

[2] Phys.org, 2015, „Saharan silver ants can control electromagnetic waves over extremely broad spectrum range“
http://phys.org/news/2015-06-saharan-silver-ants-electromagnetic-extremely.html

[3] http://broom02.revolvy.com/main/index.php?s=Saharan%20silver%20ant%40wiki%3ASaharan_silver_ant

[4] Scientific Comittees
http://ec.europa.eu/health/scientific_committees/opinions_layman/en/electromagnetic-fields/glossary/ghi/heat-shock-proteins.htm

[5] Jennifer Langston , 2015, „Saharan silver ants use hair to survive Earth’s hottest temperatures“
http://www.washington.edu/news/2015/06/18/saharan-silver-ants-use-hair-to-survive-earths-hottest-temperatures/

[6] O. M. Kamiyo, D. Angeli, G. S. Barozzi, M. W. Collins, V.O.S. Olunloyo and S.O. Talabi, 2011, „A Comprehensive Review of Natural Convection in Triangular Enclosures“
http://appliedmechanicsreviews.asmedigitalcollection.asme.org/article.aspx?articleid=1399776

[7] http://phys.org/news/2016-04-saharan-silver-ant-hairs-thermoregulate.html

[8] http://ibnuradinas.blogspot.se/2010/12/sang-murabbi-murabithun.html

[9] http://islamic-arts.org/2012/mosque-of-cordova/

[10] http://www.cawardenreclaim.co.uk/reclaimed-red-angled-wall-coping.html

[11] https://www.dreamstime.com/stock-photo-triangular-clay-tile-wall-terracotta-orange-image74967167

[12] https://www.pinterest.com/ShelleyKing80/carpet-tiles-and-flooring/

[13] https://www.pinterest.com/pin/69242912993397439/

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