Engineers have turned to pine cones as inspiration for a new way to reduce the energy used by buildings. By mimicking the way these woody fruits open in response to humidity, the researchers have made shades that can open and close without using any electricity.
Folding shades that adjust the amount of sunlight hitting a building have been around for a while. By helping to regulate temperature, they reduce the cooling burden of a building. Such shading systems today work with electrically-driven motors.
Buildings account for around 40 percent of global energy use and carbon dioxide emissions, according to the International Energy Agency. A big chunk of this energy consumption is for cooling, and the use of energy for cooling is growing faster than any other end use in buildings. Researchers have been coming up with cooling films, aerogel window coatings, and other high-tech materials to cut cooling energy use.
Chiara Vailati and her colleagues at ETH Zurich instead turned to good old wood to make a low-tech, sustainable shading system that adjusts its shades throughout the day without the need for any sensors and motors. Instead, the shades open and close in response to their environment.
The mechanism is based on pinecones, which keep seeds safe by tightly closing their scales when it’s wet and cold. The scales open to disperse seeds when the weather is dry and warm. The secret behind this is simple: the scales are made of two different layers with fibers that oriented perpendicular to each other. When moisture in the air decreases, the two layers contract differently, making the scales go from straight to curved so the cone opens up.
The new shading device, reported in the journal Energy and Buildings, have panels made of two different kinds of wood: spruce and beech. The panels are joined in a way that the grain of two kinds of wood are oriented perpendicular to each other.
Next, the researchers couple two such wood panels together so that one is suspended over the other one, which is vertical. The shading device is meant to be mounted horizontally like an awning as opposed to vertically like blinds.
When the air is humid, such as at night, early mornings, and when the sky is overcast, the planks sit almost flat against each other. But as it gets sunny and the air heats up and dries, the panels bend so that the lower one pushes the upper one out and makes it horizontal, producing shade.
“I wanted the system to be made of environmentally friendly materials, use very little energy, and have low installation and maintenance costs,” Vailati said in a press release.
Source: C. Vailati et al. An autonomous shading system based on coupled wood bilayer elements. Energy and Buildings, 2018.