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Passive radiative cooling in delignified wood material

May 23, 2019

A newly engineered, wood-based material successfully reflects heat, or infrared radiation, and could cut the energy costs associated with cooling buildings by up to 50%, according to a modeling analysis of its application in 16 U.S. cities. The brilliant white "cooling wood," which is more than eight times stronger than natural wood, is both highly reflective and capable of passive radiative cooling - two highly-sought after properties in next-generation, energy-efficient structural materials. Buildings account for more than 40% of the nation's total energy demand - nearly half of which is used for heating and cooling, often through energy-inefficient means. Cooling indoor environments is particularly challenging and energy-intensive, which has made passive radiative cooling an attractive alternative for improving the energy efficiencies of buildings. Passive radiative cooling materials can cool a structure by deflecting incoming solar radiation and dissipating heat energy with no energy consumption. While several methods for achieving passive radiative cooling in buildings have been demonstrated experimentally, the ability to manufacture and implement the systems at the size and scale necessary for widespread adoption remains unfeasible. By compressing wood that has been stripped of its lignin (polymers that help make plant cells rigid), Tian Li and colleagues enhance the qualities of the already widely used, sustainable construction material and imbue it with impressive mechanical and radiative cooling properties. According to Li et al., the complete delignification and densification process not only makes the wood significantly stronger, but also results in partially aligned cellulose nanofibers, which gives the cooling wood its highly solar reflective surface, and high infrared emissivity. Testing of the cooling wood's radiative flux demonstrated continuous sub-ambient cooling during day and night. What's more, a cooling cost evaluation across 16 U.S. cities finds savings between 20% and 50%.
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American Association for the Advancement of Science

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