New ‘chameleon-like’ building material can change color to save energy

“This kind of smart material lets us maintain the temperature in a building without huge amounts of energy.”

Deena Theresa
New ‘chameleon-like’ building material can change color to save energy
Representational image.

ASKA/iStock 

Researchers at the University of Chicago’s Pritzker School of Molecular Engineering (PME) have developed an interesting solution to regulating the temperature of buildings.

They designed a “chameleon-like” building material that changes its infrared color and the amount of heat it absorbs and emits based on the temperature outside. To elaborate, the material can emit up to 92 percent of the infrared heat it contains, thereby cooling the inside of a building. And on colder days, the material emits just seven percent of its infrared, helping keep a building warm.

“We’ve essentially figured out a low-energy way to treat a building like a person; you add a layer when you’re cold and take off a layer when you’re hot,” assistant professor Po-Chun Hsu, who led the research, said in a statement. “This kind of smart material lets us maintain the temperature in a building without huge amounts of energy.”

The study is published in Nature Sustainability.

The material contains a layer that can take on two conformations: solid copper that retains most infrared heat, which helps keep the building warm; or a watery solution that emits infrared, which can help cool the building.

We need buildings that can adapt to extreme and variable weather conditions

According to a study, buildings consume almost 151 EJ energy, equivalent to 36 percent of the world’s final energy consumption. And around 30 percent of the global energy consumption is used for the operation of buildings. They emit 10 percent of all global greenhouse gas. Half of this energy footprint can be traced to the heating and cooling of interior spaces.

“For a long time, most of us have taken our indoor temperature control for granted without thinking about how much energy it requires. If we want a carbon-negative future, I think we have to consider diverse ways to control building temperature in a more energy-efficient way,” said Hsu.

With global warming causing extreme weather events, we must create buildings that can adapt to variable weather.

The new building material is mom-flammable and electrochromic

Hsu and colleagues designed a non-flammable “electrochromic” building material that contains a layer that can take on solid copper that retains most infrared heat or a watery solution that emits infrared. 

The device uses a tiny amount of electricity to trigger the chemical shift between these states by either depositing copper into a thin film or stripping that copper off.

The device can switch “rapidly and reversibly between the metal and liquid states” and effectively switch between the two conformations even after 1,800 cycles.

The team then created models of how their material could cut energy costs in buildings in 15 different U.S. cities. According to them, “the electricity used to induce electrochromic changes in the material would be less than 0.2 percent of the total electricity usage of the building but could save 8.4 percent of the building’s annual HVAC energy consumption”.

Hsu Group created models of how their material could cut energy costs in typical buildings in 15 different U.S. cities.

Towards a sustainable future

The researchers are now investigating different ways of fabricating the material. 

Until now, the team has created pieces of the material that measure only six centimeters across. However, many such patches of the material could be assembled like shingles into larger sheets and the material could also be tweaked to use different, custom colors without hindering its ability to absorb infrared.

“We demonstrated that radiative control can play a role in controlling a wide range of building temperatures throughout different seasons,” said Hsu. “We’re continuing to work with engineers and the building sector to look into how this can contribute to a more sustainable future.”

Study Abstract:

Radiative thermoregulation can reduce the energy consumption for heating, ventilation and air-conditioning (HVAC) in buildings, and therefore contribute substantially to climate change mitigation. Electrochromism, a phenomenon in which a material exhibits reversible colour changes under an external electrical stimulus, can help control the heat balance of buildings in response to fluctuating weather conditions; however, its implementation has been largely limited to visible and near-infrared wavelength regimes. Here we develop an aqueous flexible electrochromic design for use as a building envelop based on graphene ultra-wideband transparent conductive electrode and reversible copper electrodeposition, in which the thermal emissivity can be tailored to vary between 0.07 and 0.92 with excellent long-term durability. Building energy simulations show that our design as building envelopes can save on year-round operational HVAC energy consumption across the United States by up to 43.1 MBtu on average in specific zones. Such dynamic emissivity tunability can further serve as a non-destructive technological solution to retrofit poorly insulated or historic buildings. Our work suggests a feasible pathway to radiative thermoregulation for more energy-efficient HVAC and solving some of the global climate change issues.