When people think of wood in a house, the first thought is logs in a fireplace to provide extra warmth. But researchers at the University of Maryland and the University of California have another idea—harnessing the intricate structure of processed wood to develop a passive cooling method that could save homeowners energy.
The method involves using the tiny structures found in specially processed wood—cellulose nanofibers and the natural chambers that grow to pass water and nutrients up and down inside a living tree—that radiate heat away. The research was published in the journal Science.
“This work has greatly extended the use of wood toward high-performance, energy-efficient applications and provided a sustainable route to combat the energy crisis,” says Jian Li, a Northeast Forestry University Professor and a member of Chinese Academy of Engineering. Li is not associated with the research.
The University of Maryland researchers include Liangbing Hu, and co-first authors Tian Li and Shuaiming He. Hu’s team has invented a range of emerging wood nanotechnologies, including a transparent wood, low-cost wood batteries, super strong wood, super thermal insulating wood, and a wood-based water purifier. The scientists explain their work in the video below.
The University of Colorado at Boulder research team is led by Prof. Xiaobo Yin and includes co-first author Yao Zhai, both of the department of mechanical engineering and the program of materials science. The scientists have been working on materials for radiative cooling, including thin films and paints.
“When applied to buildings, this game-changing structural material cools without the input of electricity or water,” Dr. Zhai says.
By removing the lignin, the part of the wood that adds the brown color and strengthens the material, University of Maryland researchers created a very pale wood. The wood was then compressed to restore its strength. The researchers added a super hydrophobic compound that helps protect the wood against moisture. The resultant white building material could be used for roofs to radiate heat out from inside the building.
During tests on a farm in Arizona, the researchers found that the wood stayed, on average, five or six degrees cooler than the ambient air temperature—even during the hottest part of the day. It stayed on average 12 degrees cooler than natural wood, which warms up more in the presence of sunlight.
“The processed wood uses the cold universe as a heat sink and release thermal energy into it via atmospheric transparency window. It is a sustainable material for sustainable energy to combat global warming,” Dr. Li says.