Key Takeaways
- Researchers from Berkeley Lab and UCLA have created a material that pumps heat away from the source.
- Thin, stacked polymer layers move toward and away from each other, transferring heat from layer to layer.
- The heat pump does not require refrigerant or other liquids, only a small amount of electricity. It could be used to make clothing or devices that cool people efficiently during extreme heat events.
What if advanced clothing or accessories could cool people down fast, no matter where they are? Researchers from the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California Los Angeles (UCLA) have demonstrated a new material design that could make this possible with minimal electricity.
The technology involves thin, shape-shifting film layers that pump away heat, cooling the surrounding air. A proof of concept, described in a paper published by the journal Science, lowered ambient temperatures by 16 degrees Fahrenheit within 30 seconds, and readings at the edge of the device dipped as low as 25 degrees.
"Instead of cooling a whole room in a building, our technology could provide comfort in the form of wearable or small-space devices that use very little electricity."
–Sumanjeet Kaur
Similar to the way heated jackets, gloves, and other portable warmers have made it easier for people to withstand frigid temperatures, localized cooling devices could provide relief during heat waves.
"Instead of cooling a whole room in a building, our technology could provide comfort in the form of wearable or small-space devices that use very little electricity," said Sumanjeet Kaur, staff scientist at Berkeley Lab and paper coauthor.
Adding Layers to Keep Cool
The researchers' heat pump uses electrocaloric cooling, a phenomenon where certain materials temporarily change temperature in response to an electric field. Electrocaloric materials on their own, however, won't produce a cooling effect that is large enough. They need to be paired with a transfer mechanism that continually moves heat.
Rather than depending on a separate pump or actuator, which would add bulk and consume more energy, the researchers designed an elegant solution based on stacked layers of electrocaloric materials. The layers serve as a heat pump, moving warmth from the layer closest to the heat source away to the outermost layer.
Kaur began exploring localized cooling technologies as part of a Berkeley Lab Laboratory Directed Research and Development (LDRD) award. One goal of the project, which began in 2022, was to optimize electrocaloric materials and enable their use in a wearable cooling device such as clothing or a blanket.
An expert on thermal energy storage, Kaur teamed with principal investigator Qibing Pei, a professor of materials science and engineering at the UCLA Samueli School of Engineering, to explore the cooling potential of an electrocaloric material called poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethy-lene) terpolymer, or P(VDF-TrFE-CFE). They published a paper with their colleagues last February which demonstrates that making this terpolymer film using a mix of solvents could achieve higher differences in temperature (i.e., more cooling) than typical synthesis methods.
This enhanced material is the basis of the proof-of-concept heat pump demonstrated in the Science paper. Six polymer film discs, each about an inch in diameter and coated with carbon nanotubes, were stacked together. The nanotubes function as conductors for the electric field that stimulates the material. Applying voltage to alternating films in the stack causes the layers to move toward and away from each other, transferring heat from layer to layer and away from the source.
Liquid-Free Cooling
Unlike most air conditioning units, the electrocaloric system does not rely on refrigerants or water. Using this kind of hyperlocal cooling can also save energy and reduce stress on the grid by keeping people cool while allowing for higher thermostat settings in buildings.
The patent pending technology was a result of a joint effort between UCLA and Berkeley Lab. The researchers noted that increasing the materials' thermal conductivity and insulating the stack from ambient air should substantially increase the concept's cooling power. They are pursuing funding to build a prototype, Kaur said, with an eye toward scaling up the device from the study and gauging its long-term performance.
The research was funded by the Laboratory-Directed Research and Development (LDRD) program at Berkeley Lab, the Office of Naval Research, UCLA's California NanoSystems Institute, and the Defense Advanced Research Projects Agency.
