Color-Changing Material Adjusts Building Temperature
Researchers from the University of Chicago’s Pritzker School of Molecular Engineering have reportedly designed a building material that changes its infrared color based on the outside temperature.
“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,” said Assistant Professor Po-Chun Hsu, who led the research recently published in Nature Sustainability. “This kind of smart material lets us maintain the temperature in a building without huge amounts of energy.”
About the Material
Hsu and the team have reportedly designed a non-flammable “electrochromic” building material that contains a layer that can take on two conformations. A solid copper can retain most infrared heat, while a watery solution emits infrared.
The device can then use a tiny amount of electricity at any chosen trigger temperature to induce the chemical shift between the states by either depositing copper into a thin film or stripping that copper off.
The University of Chicago reports that on hot days the material can emit up to 92% of the infrared heat it contains, helping cool the inside of a building. However, on colder days, the material emits just 7% of its infrared to help keep a building warm.
The researchers found in their study that the device can switch rapidly and reversibly between the metal and liquid states. They showed that the ability to switch between the two conformations remained efficient even after 1,800 cycles.
Afterwards, the team created models of how their material could cut energy costs in typical buildings in 15 different U.S. cities. They reported that in an average commercial building, the electricity used to induce electrochromic changes in the material would be less than 0.2% of the total electricity usage of the building, but could save 8.4% of the building’s annual HVAC energy consumption.
“Once you switch between states, you don’t need to apply any more energy to stay in either state,” said Hsu. “So for buildings where you don’t need to switch between these states very frequently, it’s really using a very negligible amount of electricity.”
According to the university’s release, the research was driven by climate change, with buildings estimated to account for 30% of global energy consumption and emit 10% of all global greenhouse gases. About half of this footprint is reportedly attributed 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,” said Hsu. “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.”
While so far the researchers have only made pieces of the material that measure six centimeters across, they eventually aim to create patches that could be assembled like shingles into larger sheets. The material could also reportedly be changed to use different, custom colors.
The team is now investigating different ways of fabricating the building material, with plans to probe how intermediate states of the material could be useful.
“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.”
Recent Energy Saving Research
Last month, it was reported that a new multilayered fluidic system developed by researchers at the University of Toronto has the potential to reduce energy costs in buildings. Inspired by the skin of a certain species of squid, the team developed a platform that optimizes the wavelength, intensity and dispersion of light transmitted through windows using microfluidics. The prototypes reportedly consist of flat sheets of plastic that are permeated with an array of millimeter-thick channels to pump fluids through.
Then, customized pigments, particles or other molecules can be mixed into the fluids to control what kind of light gets through and in what direction the light is distributed. The sheets can also be combined into a multi-layered stack with different optical functions, such as controlling intensity, filtering wavelength or tuning the scattering of transmitted light indoors.
This method can be digitally controlled by pumps to add or remove fluids from each layer, optimizing light transmission within the system.
According to the release, the study was inspired by multilayered skin of a squid, which contains stacked layers of specialized organs. This includes chromatophores and iridophores, which control light absorption and impact reflection and iridescence, respectively.
U of T researchers reportedly built detailed computer models that analyzed the potential energy impact of covering a hypothetical building in this type of dynamic façade, informed by physical properties measured from their prototypes. The team also then simulated various control algorithms for activating or deactivating the layers in response to changing ambient conditions.
In November, a group of researchers published a study on a new transparent window coating that could be utilized to lower the temperature inside buildings. The team set out to design a “transparent radiative cooler” (TRC) using advanced computing technology and artificial intelligence.
In the study’s abstract, researchers described that the TRC was developed on the basis of layered photonic structures using a quantum computing-assisted active learning scheme, which combines active data production, machine learning, and quantum annealing in an iterative loop.
By alternating thin layers of common materials like silicon dioxide, silicon nitride, aluminum oxide or titanium dioxide on a glass base topped with a film of polydimethylsiloxane, researchers said they were able to optimize a coating design that, when fabricated, beat the performance of conventionally designed TRCs.
In addition, the team wrote that the resulting coating design performed better than one of best commercial heat-reduction glasses on the market.
The best-performing TRC developed from the study has the potential to reduce cooling energy consumption by 31% compared with conventional windows, according to the study authors. The coating also has the potential to be utilized in other applications, such as car and truck windows.