Lilley and corresponding author Ravi Prasher, a research affiliate in Berkeley Lab’s Energy Technologies Area and adjunct professor in mechanical engineering at UC Berkeley, laid out the theory underlying the ionocaloric cycle. They calculated that it has the potential to compete with or even exceed the efficiency of gaseous refrigerants found in the majority of systems today.
They also demonstrated the technique experimentally. Lilley used a salt made with iodine and sodium, alongside ethylene carbonate, a common organic solvent used in lithium-ion batteries.
“There’s potential to have refrigerants that are not just GWP [global warming potential]-zero, but GWP-negative,” Lilley said. “Using a material like ethylene carbonate could actually be carbon-negative, because you produce it by using carbon dioxide as an input. This could give us a place to use CO2 from carbon capture.”
Running current through the system moves the ions, changing the material’s melting point. When it melts, the material absorbs heat from the surroundings, and when the ions are removed and the material solidifies, it gives heat back. The first experiment showed a temperature change of 25 degrees Celsius using less than one volt, a greater temperature lift than demonstrated by other caloric technologies.
“There are three things we’re trying to balance: the GWP of the refrigerant, energy efficiency, and the cost of the equipment itself,” Prasher said. “From the first try, our data looks very promising on all three of these aspects.”
While caloric methods are often discussed in terms of their cooling power, the cycles can also be harnessed for applications such as water heating or industrial heating. The ionocaloric team is continuing work on prototypes to determine how the technique might scale to support large amounts of cooling, improve the amount of temperature change the system can support, and improve the efficiency.
“We have this brand-new thermodynamic cycle and framework that brings together elements from different fields, and we’ve shown that it can work,” Prasher said. “Now, it’s time for experimentation to test different combinations of materials and techniques to meet the engineering challenges.”
Lilley and Prasher have received a provisional patent for the ionocaloric refrigeration cycle, and the technology is now available for licensing by contacting email@example.com.
This work was supported by the DOE’s Energy Efficiency and Renewable Energy Building Technologies Program.
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