Life; not the first thing that comes to mind when someone thinks about the desert and there is good reason for that. But then again life is by definition the only showcase of survival stories, so why discard the thought?
Paradoxical as this image might seem, it is a glorious representation of how nature’s life forces can overcome its most inhospitable manners. In search of an efficient way for humans to inhabit the arid desert, nature’s structures could provide solutions. This solitary acacia in the middle of the Sahara effortlessly raises the question:
No surprise, the answer is water. Not a long dig below the desert surface, the soil contains liquid H2O. Also dubbed “capillary water”, the liquid is trapped under the desert soil and its extraction requires immense amounts of pressure. Luckily, through a process far more complicated than what is widely known as capillary action, trees employ a passive way of extracting water from the ground and having it distributed along their whole body, the humble desert shrub being the champion in doing so.
Water has been used for centuries in vernacular desert architecture as a cooling agent via transpiration, enabled by the use of indoor pools and fountains. Vegetation is also a widely used means of temperature control in milder climates, mainly in the form of outdoor plants releasing moisture in wind circulation. Combining forces with fountain transpiration, moisture released from indoor vegetation could possibly result in drastic temperature drops. Keeping that moisture inside and managing its circulation is the subsequent challenge.
Going one step further, such a process would ideally be materialized by being integrated into the building itself; developing an organic module that is able to extract water from the ground distribute it across its mass and prevent it from escaping would massively benefit the passive cooling process. Additional strategies to release the water and stir it into the indoor environment can be looked for in nature.
Technological advancements that would aid in engineering bio-building-blocks as nature engineers its flora have either been made or are in development.
The world’s first synthetic tree was created by researcher Abraham Stroock and graduate student Tobias Wheeler at Cornell University back in 2008. The result bears no resemblance to a tree in terms of appearance, but aims to simulate its function, mainly the process of transpiration and capillary action.
The palm-sized bio-mechanism consists of two discs made out of porous hydrogel; the “root” disc wicks moisture in via capillary action which is then sucked into the “leaves” disc through a micrometer-sized tube by negative pressure and released through smaller artificial stomata, commencing the transpiration cycle.
“It would be nice if you could, in a building, put these passive elements […] to deliver heat all the way down through the building, then recycle that fluid back up to the roof the same way trees do it — pulling it back up” says Stroock
Integrating the above strategy in the building shell itself could lead to fascinating results. Not only would it provide a way to harvest the hard-to-get water out of the soil, but it could possibly come with the bonus behaviour of hydrogel in passive cooling applications, as demonstrated by students of the Institute of Advanced Architecture in Catalonia.
Hydrogel can absorb close to four hundred times its volume in water, slowly releasing it back to the atmosphere via evaporation. This can translate to a vastly improved wall thermal capacity in addition to constant heat resistance through evaporative cooling.
Simplifying the design process and maintaining a connection to vernacular practices, this moisture distribution technology could be ideally developed in bricks that can later be arranged according to needs and intentions and following similar nature-inspired strategies. Further support for this idea comes in the form of CoolBrick, a construction module designed for natural air conditioning through evaporative cooling. The bricks are 3D-printed from clay and organic matter; micropores on their surface hold on to water and help bring the room temperature down.
The project was inspired by the Muscatese evaporative cooling window, which combines a mashrabiya and a ceramic vessel filled with water and backed by additional research on porous ceramic cooling carried out at the University of Nottingham’s School of the Built Environment.
Having secured water intake from the ground and employing methods of utilizing it as a cooling mechanism will not take things far if steps are not taken towards preventing its escape under the effect of unbearable desert heat. The building skin needs to facilitate that function and for that purpose too inspiring examples can be borrowed from natural processes.
Take the Darkling Beetle of the Namib Desert as an example. Inhabitants of one of the world’s driest environments, some species of the beetle have developed methods for acquiring precious water from dew and ocean fog. Tiny, micro-sized bumps on the beetles’ forewings aid in condensing water and directing it towards its mouth. Scientists are studying the beetle along with synthetic surfaces designed to mimic its shell to determine what combination of structure, chemistry, body stance and orientation contributes to its ability of water harvesting. Other desert creatures like the Thorny Devil and the Texas Horned Lizard employ similar strategies of body stance and surface grooves to gather water from their surroundings while the Desert Lark, a resident bird of the desert, prevents water from escaping via a ceramide-rich lipid ratio in its skin. Studying such strategies and applying a relevant inner skin layer to a building block could be a vital step towards achieving highly efficient water loss prevention.
These practices could in theory provide a humid interior capable of sustaining plant life, but it is plant life itself that would set concrete foundations for a contained interior ecosystem. Plants in arid climates have their own way of organizing their growth to minimize water loss and sustain their survival. Assisting plant growth in the interior would greatly enhance the effects of the building shell and multiply benefits of both water intake, evaporative cooling and water loss prevention.
Designed by Pieter Hoff, a Dutch bulb grower, Groasis Waterboxx is a device that could assist plant growth in the first stages of the struggle to overcome the threatening desert conditions. Waterboxx is a container aimed at incubating one tree at a time, maintaining the ideal conditions for the first stage of their growth cycle. The design of the container eliminates the need for irrigation and additional water sources, rendering it efficient for assisting plant growth in arid climates. Constructed with bio-polymers, the containers later biodegrade to provide the growing plant with nutrients. The design of the Waterboxx is inspired by nature’s cycle of seed growth; from plant to animal to excretion to seed growth, to plants again and so on.
In addition to cooling techniques and strategies, measures need to be taken to minimize heat intake. The exterior layer of the building block skin, as well as its form, can be designed to passively regulate interior conditions. Simple gestures can combine nature’s strategies for double benefits. As mentioned above, certain animals’ skin and posture, such as the thorny devil’s ridge-strewn skin, has the ability to harvest water from the surrounding environment.
A well known example of desert flora, the cactus, also enjoys benefits from folds and ridges on its skin. Cacti are not able to reflect radiation with their skin but cope by having ribs running along their surface, shading parts of the plant while other parts are in direct sunlight. This results in pressure differences that produce air currents that improve heat radiation. Of what the cactus lacks in reflectivity, the desert snail possesses plenty.
Its highly reflective shell greatly reduces heat increase while the form of its home allows it to retreat to its top chamber, keeping a layer of air acting as a buffer zone between the animal’s body and the hot ground. This idea could be applied in a building both as material selection as well as design inspiration to achieve similar results.
Structural representations of simplified bio-brick function arrangement (not to scale)
LINKS & REFERENCES
1 Vogel S. 2003; Comparative Biomechanics: Life’s Physical World. _Princeton: Princeton University Press | pg.580
2 Ahmet Vefik, 1990; Vernacular Climate Control in Desert Architecture. _College of Environmental Design, University of Petroleum and Minerals, Dhahran (Saudi Arabia) and Alp & Alp Architects, Istanbul (Turkey) | pg.813
3 Research&Design, Fall 1979; Passive Cooling. _The Quarterly of the AIA Research Corporation | pg.8
4 Logan Osgood-Jacobs, Fabrication of Synthetic Trees for the Investigation of Water at Negative Pressures. _Swarthmore College, Engineering | pg.48
5 Rathee A., Mitrofanova E., Santayanon P., Markopoulou A. 2014; Hydroceramic. _IAAC-Digital Matter: Intelligent Construction
6 Dr Rosa Schiano-Phan, 1 June 2009; Cooling with Porous Ceramic The use of porous ceramic for passive evaporative cooling in buildings. The University of Nottingham, School of the Built Environment
7 Nørgaard T., Dacke M. 2010; Fog-basking behaviour and water collection efficiency in Namib Desert Darkling beetles. BioMed Central, Frontiers in Zoology
8 Lewis D.A., Nobel P.S. 1977; Thermal Energy Exchange Model and Water Loss of a Barrel
Cactus, Ferocactus acanthodes. Department of Biology, University of California
9 Schmidt-Nielsen K., Taylor C.R., Shkolnik A. 1971; Desert Snails: Problems of Heat, Water and Food. Department of Zoology, Duke University, Durham, NC