Heating and cooling account for most of the energy used in homes and businesses, according to the U.S. Energy Information Administration. Additionally, heat gain and loss through windows can waste up to 30% of the energy used to heat and cool a home. With this in mind, a research team at Penn State is exploring the development of smart windows that use a unique polymer to block sunlight. On the latest episode of "Growing Impact," the team discusses how the material works and how these smart windows might change the way buildings are designed, built and operated.
"We like to live in buildings that are the perfect temperature, but that comes with a cost because it's very expensive to heat or cool a building," said Patrick Mather, professor of chemical engineering and of material science and engineering as well as a team member. "We have a technology that will dynamically change how much light gets through, depending on how much sun is shining on it, and that will dramatically reduce the cost to keep a room or a building at a particular temperature."
Nathan Keim, associate professor of physics and principal investigator, said the heating and cooling of buildings is an ideal area for innovation as climate change places greater stress on buildings and their occupants.
"A lot of the energy that comes from the sun is not visible as light," Keim said. "Those longer wavelengths, or infrared, are why sunlight feels hot. That is a major contributor to what heats up a building."
Sebanti Chattapahyay, a postdoctoral scholar in the Department of Physics, said the smart window uses a semi-crystalline polymer with a tunable melting point set near room temperature so when the material warms, its crystals melt and trigger the change in the window to block light or energy from the sun.
"Because of its rubber elasticity, this polymer naturally wants to coil up and shrink," Chattapahyay said. "But when you stretch it and cool it, the crystals align with the stretch, and that actually makes the material elongate. Then, when it heats back up, the crystals melt and the polymer relaxes again."
The polymer can switch between short and long shapes over many cycles without degrading, making it durable, long-lasting and economically practical, according to Chattopadhyay.
Additionally, the technology operates without power or sensors, Mather said.
"The polymer only needs heat from the sun to activate, and the windows experience that heat as soon as sunlight hits them," he said.
"Growing Impact" is a podcast by the Institute of Energy and the Environment. It features Penn State researchers who have been awarded IEE seed grants and discusses their foundational work as they further their projects. The podcast is available on multiple platforms, including YouTube, Apple, Amazon and Spotify.
