Scientists have designed a novel type of wood that radiates heat away, paving the way for building materials that could keep homes cool and help save on electricity bills.
Researchers at the University of Maryland and the University of Colorado in the US have harnessed nature's nanotechnology to help solve the problem of finding a passive way for buildings to dump heat that is sustainable and strong.
Wood is already used as a building material, and is renewable and sustainable, they said.
Using tiny structures found in wood -- cellulose nanofibres and the natural chambers that grow to pass water and nutrients up and down inside a living tree -- the specially processed wood has optical properties that radiate heat away, according to the study published in the journal Science.
"Cooling wood that is made of solely wood -- that is, no any other component such as polymers -- can cool your house as a green building material," said Liangbing Hu, from the University of Maryland.
"When applied to building, this game-changing structural material cools without the input of electricity or water," said Yao Zhai, from at the University of Colorado.
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By removing the lignin, the part of the wood that makes it brown and strong, the researchers created a very pale wood made of cellulose nanofibres.
They then compressed the wood to restore its strength. To make it water repellent, they added a super hydrophobic compound that helps protect the wood.
The result is a bright white building material that could be used for roofs to push away heat from inside the building.
Researchers tested the cooling wood and found that it stayed, on average, five or six degrees cooler than the ambient air temperature -- even at the hottest part of the day, the cooling wood was chillier than air.
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 heat sink and release thermal energy into it via atmospheric transparency window. It is a sustainable material for sustainable energy to combat global warming" said Tian Li, of University of Maryland.
The mechanical strength per weight of this wood is also stronger than steel, which makes it a great choice for building materials, researchers said.
It also damages less easily and can bear more weight than natural wood.
Researchers estimate that the material would save on average 20 per cent of cooling costs.