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A new material could provide smart cladding for buildings that alters how much heat they absorb or emit by changing their infrared colour with the flick of a switch, similar to sunglasses that turn dark when exposed to light.

Usually, a building鈥檚 temperature is controlled using air conditioning or heating units. But this is an energy-intensive and polluting way of managing things.

Buildings are responsible for about 40 per cent of global energy consumption and 33 per cent of greenhouse gas emissions, .

at the University of Chicago and his colleagues set out to design a new, greener way of controlling a building鈥檚 temperature, more akin to how people manage their temperature while out and about.

鈥淲e don鈥檛 carry a heater or air conditioning around with us. We add or remove layers,鈥� says Hsu. 鈥淲e take that similar concept and apply that to the building level.鈥�

The end result is thin panes that, once covering a building, control the structure鈥檚 infrared colour and how much heat it absorbs or emits.

This kind of dynamic temperature control can allow the building to respond to changes in the outside air temperature, says Hsu. On a warm day, the panes can release up to 90 per cent of the building鈥檚 heat to keep the inside cool. On a colder day, the panes release as little as 7 per cent of the building鈥檚 retained heat, helping to keep the interior warm.

鈥淚f we can suppress heat loss through radiation during wintertime, or we can increase heat loss during summertime, then we can achieve this dynamic insulation without consuming heating or air conditioning energy,鈥� says Hsu.

The system works by encasing a watery electrolyte solution inside two panels. The solution can turn into a sheet of solid copper when an electrical current is applied. The solid sheet retains heat, while the solution lets heat escape. The system uses only a tiny amount of power to apply the current, says Hsu.

This kind of electrochromic reaction usually changes the colour of the material, like in smart sunglasses that can adjust the tint of a lens, for example. Colour-changing buildings would be possible using this technology, but Hsu says they can also design the panes so that only invisible infrared waves are affected, keeping the building鈥檚 appearance stable to the naked eye.

So far, Hsu and his team have only built small panels measuring about 6 centimetres across. But if thousands of patches were used to coat an entire building, it could cut the structure鈥檚 energy demand by more than 8 per cent, they estimate.

Hsu now plans to work with other researchers to carry out a life cycle assessment of the panels to determine whether the environmental cost of constructing, installing and operating them would outweigh the potential energy-saving benefits.

He is one of a number of researchers investigating the potential of infrared to regulate heat loss in buildings. But at Nanyang Technological University in Singapore says that while this method of temperature control may work for windows, it may not be necessary for the walls of modern, well-insulated buildings.

鈥淢ost building walls in temperate countries are designed as good insulators already, so the walls will not allow much conducted heat to pass through on a hot day anyway,鈥� he says.