Wood foam passively cools buildings to reduce energy bills

Much of the energy consumption goes to heating and cooling homes and buildings, so it is important to find new ways to passively regulate temperature. Engineers in China and Germany have developed a new wood-based foam that can drastically cool buildings to an easily adjustable degree.

Air conditioning is efficient, but it is not the most environmentally friendly way to cool down. In recent years, scientists have developed techniques that do not absorb as much electricity, including super-white paints or mirror coatings that reflect sunlight, and radiation cooling systems that radiate heat to the building like infrared waves in the sky where it passes directly through the atmosphere. and is released into the cold of outer space.

But the effectiveness of these systems can vary under different conditions. Reflective coatings, for example, can still leak heat if it is particularly hot or humid, while radiative cooling does not work as well if it is cloudy. The cooling level can also be difficult to adjust.

Now scientists from the University of Göttingen and the University of Forestry in Nanjing have created new material that they believe solves some of these problems. In essence, it is a foamy substance made of wood that reflects sunlight, acts as thermal insulation and radiates absorbed heat back into the atmosphere.

It is made of cellulose nanocrystals bonded to a silane bridge, which is then freeze-dried into a white, light foam. The final product reflects 96 percent of the visible light from the sun and emits 92 percent of the infrared radiation it absorbs.

To test the cooling capacity of the material, the researchers placed it on a box lined on the inside with aluminum foil and placed it in direct sunlight at noon. The material kept the inside of the box 16.5 ° F (9.2 ° C) cooler than the outside air, and even in humid weather kept the inside 13.3 ° F (7.4 ° C) cooler. If it increases to the roof and walls of a building, researchers estimate it could reduce cooling energy needs by an average of 35 percent.

Most intriguingly, the cooling power of the foam decreases if compressed. This may sound like a drawback, but the team suggests that squeezing the foam can be a useful way to fine-tune the amount of cooling according to weather or environment.

Researchers say the new cooling foam may eventually pave the way for thermally regulating materials that are not only environmentally friendly but also reduce the cost of energy used for cooling.

The study was published in the journal Nano letters.

Source: American Chemical Society