Constructal Theory: 5 Designs Shaping the Future of Sustainable Engineering

Constructal Leaf Image

photo Jenny Downing@Flickr
What Is Constructal Design and Can It Save The World?
Take a look at a leaf, like the one above. Notice the elegant branching pattern of the veins. This is a constructal design. If you were to look at a river from an airplane, or the pathways in our lungs, these are also constructal designs. Scientists and engineers are beginning to realize that these forms can be explained and predicted by a universal theory of flow structures--constructal theory. Those who apply this understanding to design, are creating a new engineering and design science of constructal design.

We at TreeHugger made a go of exploring constructal theory and its application to sustainability several years ago. Since then, more people have picked up the concept, and there is growing excitement that constructal design may hold several keys to developing a more sustainable world. We count down the top five potential wins for constructal design and sustainability.

Constructal Computer image

photo corego @ flickr

1. Harder, Better, Faster, Stronger...Computers

One of the limits to computer speed is keeping them cool. As anyone who uses a laptop on their lap will tell you, engineers have used heat sinks to shunt the heat away from the all important processor and towards the exterior of the machine. If an engineer used a constructal design approach, it would turbo boost this energy movement, creating a hotter lap, and cooler laptop. Alternatively engineers could decide to shunt the heat away from more sensitive areas, and this would help future generations of computer geeks to enjoy constructal design as well.

But this is not just for comfort sake. Server farms, the bedrock of Web 2.0 services and companies like Google, depend on keeping their computers cool. This thermal transfer and is a major cost for the company and for the environment in terms of energy use. Applying constructal theory principles to sever farm design could create large benefits for the environment as well as the economy.

IBM has already ingenuously used a constructal approach to achieve more efficient cooling of their processors, but it's not what you might expect. A constructal design approach allowed them to better distribute the thermal paste that connects the heat sink to the heat source, this improved connection through the paste makes all the difference, and led to a nearly ten fold improvement in thermal performance.

Constructal House Photo

photo Jeremy Levine @ Flickr

2. Energy Efficient Homes and Buildings

It has been estimated that energy use in buildings accounts for one third of global greenhouse gas emissions. The US Department of Energy shows that half of all energy use in the building is caused by heating, cooling, and ventilation.

Building Energy Use Image

photo via DOE

Buildings need to bring in air from the outside, to exchange with air from inside. This can be a problem. In New England in the winter it can be 20 degrees Fahrenheit outside, and 67 degrees in my toasty computer room. If I were to open my window, I would soon be unhappy. Most houses or buildings deal with the temperature difference by heating the outside air as it enters the house. The most extreme design, and one that is growing in popularity, is the Passive House, which strictly controls the air exchange through a heat exchanger--where the cool air from outside passes next to the hot air from inside.

A passive house can save 90% of the energy of heating a house in this way. But it could get even better. Constructal design has already led to one of the worlds most efficient heat exchange devices. If architects and engineers were to look at the interfaces between the outside and inside of a house through constructal design, it may be possible bring in fresh air from outside, cool and heat the building, while also reducing the total energy cost of a building.

resilient agriculture image

photo teudimundo @ Flickr

3. Resilient Agriculture

Industrial agriculture feeds the world, but it also relies heavily on fossil fuel inputs as fertilizer, and insect chemical sprays. One reason our food needs so much fossil fuels is that we tend to plant a monoculture of annual plants that suck the nutrients out of the soil, and are sitting ducks for hungry insects. It has long been known that growing a polyculture (think corn, beans, squash) results in better soil, better yields, and more insect resistance. Yet, people often wonder how poly should that polyculture really be? Do we need 4 different kinds of plants, or 400? Constructal design can begin to answer this questions.

Through using a constructal approach it is possible to define an optimal 'complexity' for a polyculture, and may even be able to point out which different species need to be grown when, and where. A well thought out polyculture will confuses insects, keep nutrients within the soil, reduce water use, and even increase the yields of production.

It has been shown that a native grass prairie yields 238% more biomass than a monoculture. The native prairie is a naturally selected polyculture. We might be able to come close to those kinds of efficiencies with a optimized constructal polyculture. This concept is still at the early stages of development, but a constructal agriculture system could have dramatic impact on human as well as ecological health.

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