As global summer temperatures rise, more buildings are installing energy-hungry air conditioners. It might be easier to just keep your AC on all day and night, but it’s definitely going to increase your monthly bills. Also, it is not the most environmentally friendly way to cool off.
A passive cooling strategy without any electricity input has shown a significant impact on overall energy consumption globally. However, designing tunable daytime radiative cooler to meet the requirement of different weather conditions is still a big challenge, especially in hot, humid regions.
Now, engineers in China and Germany have designed a lightweight foam made from wood-based cellulose nanocrystals that reflects sunlight, emits absorbed heat, and is thermally insulating. They say the material could reduce a building’s cooling energy needs by more than a third.
The new cooling material is made out of cellulose nanocrystals, connected with a silane bridge before freezing and freeze-drying the material under a vacuum. This process vertically aligned the nanocrystals, making a white, lightweight foam, which reflected 96% of visible light from the Sun and emitted 92% of the infrared radiation it absorbs.
To test the material’s cooling ability, researchers place it over an aluminum foil-lined box sitting outdoors at noon. The material kept the temperature inside the box 16 degrees F cooler than outside of it. Also, the material kept the inside of the box 13 degrees F cooler when the air was humid. The team estimated that placing the foam on the roof and exterior walls of a building could reduce its cooling energy needs by an average of 35.4%.
The cellulose-based foam’s cooling ability decreased when it was compressed, revealing tunable cooling properties. Because the wood-based cellulose foam’s performance can be tuned depending on weather conditions, the researcher says that the technology could be applied in a wide range of environments.
The researchers say that the wood-based cooling foam could eventually pave the way toward designing high-performance, thermal-regulating materials for energy consumption savings.