This collage depicts elements related to ionocaloric cooling, a newly developed refrigeration cycle that researchers hope could help phase out refrigerants that contribute to global warming.

Scientists develop safe alternative refrigeration method

Image credit: Jenny Nuss/Berkeley Lab

Berkeley Lab scientists have introduced ionocaloric cooling, a potential alternative to refrigerants that could provide safe and efficient cooling and heating for homes.

Based on the science behind the practice of adding salt to roads to prevent ice from forming, researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a new method of heating and cooling.

Ionocaloric cooling takes advantage of the process by which energy, or heat, is stored or released when a material changes phase – such as changing from a solid to a liquid state. For example, while material absorbs heat from the surroundings, solidifying it releases heat.

Following a similar process, the Berkeley Lab team used salt ions to cause changes in temperature. They expect this new method could eventually provide efficient heating and cooling and help phase out current 'vapor compression' systems, which use gases with high global warming potential as refrigerants.

In addition, ionocaloric refrigeration would eliminate the risk of such gases escaping into the atmosphere by replacing them with solid and liquid components.

“The landscape of refrigerants is an unsolved problem: No one has successfully developed an alternative solution that makes stuff cold, works efficiently, is safe, and doesn’t hurt the environment,” said Drew Lilley, the lead researcher of the study.

“We think the ionocaloric cycle has the potential to meet all those goals if realised appropriately.”

Currently, the majority of the gases used in refrigerants are hydrofluorocarbons, or HFCs, which cause the cooling industry to be responsible for around 10 per cent of global CO2 emissions – three times the amount produced by aviation and shipping combined

In light of this significant climate impact, 145 countries have signed the Kigali Amendment, which sets a goal to reduce production and consumption of HFCs by at least 80 per cent over the next 25 years.

Ionocaloric cooling works by running current through the system, which moves the ions and changes the material’s melting point. As a result, the material absorbs heat from the surroundings. When the ions are removed and the material solidifies, it gives heat back.

Compared to other kinds of 'caloric' cooling in development, ionocaloric cooling differs by using ions to drive solid-to-liquid phase changes. Using a liquid has the added benefit of making the material pumpable, making it easier to get heat in or out of the system.

The researchers behind the study calculated that ionocaloric cooling has the potential to compete with or even exceed the efficiency of gaseous refrigerants found in the majority of systems today.

“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.”

The Berkeley team 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. 

The results of the demonstration showed a temperature change of 25ºC 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,” said Ravi Prasher, a research affiliate in Berkeley Lab’s Energy Technologies Area. 

“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.

“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.”

The researchers' findings have been described in a paper published in the journal Science.

In 2020, E&T spoke to Solar Polar, a start-up company based in Peterborough which developed a low-cost cooling solution that doesn’t require any electricity.

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