New cooling system uses salt instead of gas

Scientists in California are testing a new kind of cooling cycle that uses salt ions – not compressed gases – to move heat. With just a small electric push, the system makes a liquid shift between solid and liquid, lifting heat as it melts and dropping it as it refreezes.

In early tests from the Lawrence Berkeley National Laboratory, the approach delivered temperature shifts near 50°F (28°C) using around one volt. Because it relies on common materials instead of high-global-warming refrigerants, researchers say it could pave the way for compact, climate-safe coolers.

How salt cooling works

At its core is ionocaloric cooling, a method that shifts a material’s melting point by adding or removing ions. That change makes heat flow on demand.

When ions enter, the melting point drops and part of the solid melts, absorbing heat; when ions leave, the material crystallizes and releases heat. The cycle repeats to move heat from a cold side to a hot side.

The cycle uses electrodialysis, an electric-field process that pulls salt ions through selective membranes. That separation raises the melting point so the fluid solidifies and releases heat to the sink.

The push for safer cooling

Conventional systems rely on hydrofluorocarbons that carry high global-warming potential, a measure of heat trapping compared to carbon dioxide. Those gases can leak during manufacture, operation, or disposal.

Under a global treaty, countries have committed to cut hydrofluorocarbon use by more than 80 percent over several decades. That commitment covers production and consumption, not just emissions.

Ionocaloric mixtures avoid those gases by using solids and liquids that stay in closed loops. Ethylene carbonate and sodium iodide are early examples under study in the lab.

A recent interview noted that the refrigerant landscape remains an unsolved problem and emphasized that the goal is to develop a system that is efficient, safe, and climate-friendly.

A distinct approach to cooling

Magnetocaloric, electrocaloric, and elastocaloric approaches use large magnetic fields, high-voltages, or heavy stresses to make crystals shift. Ionocaloric cycles rely on small voltages to rearrange ions in a liquid.

That makes the transition easier to drive across a device. It also reduces the need for bulky magnets or high voltage parts.

The target is to approach the Carnot limit, the theoretical maximum efficiency set by the temperature span. Because liquids flow well through exchangers, they can move heat uniformly and avoid hot spots that waste energy.

Ionocaloric systems also operate at near-ambient pressures. Lower pressure also simplifies seals and housings.

Salt innovations reshape the cycle

Researchers continue to refine the ingredients and the plumbing. An international study described a liquid cycle that used nitrate-based salts regenerated with electric fields and membranes.

Those salts are abundant and inexpensive, which could help with scaling. The cycle logged large temperature changes while keeping efficiency competitive with early prototypes.

The new study complements the original framework rather than replacing it. It shows that several salt families can deliver the same core cooling effect with different performance trade-offs.

The bottlenecks in salt cooling designs

Power density is the sticking point today. Ion-exchange membranes designed for water have high resistance in organic solvents, which limits how much cooling power a small device can provide.

Better membranes would raise current without big losses. That single improvement could push ionocaloric devices toward the outputs needed in home-sized systems.

The separation step also dictates cost. Teams are testing layouts that recover and reuse heat internally so that less electricity is needed to move ions each cycle.

Cleaner fluids, safer cooling

The early working fluid pairs use ethylene carbonate and simple salts such as sodium iodide. Ethylene carbonate can be made using captured carbon dioxide, which could push the overall footprint lower if production scales cleanly.

Mixtures can be tuned around a eutectic – a blend that has the lowest melting point among combinations. That choice sets the cold end of the cycle.

Researchers also track coefficient of performance, cooling delivered per unit of input energy, to compare devices. Ionocaloric cycles aim for high values at practical temperature spans so real fridges and heat pumps run efficiently.

Safety benefits also come from using non-flammable working pairs. Avoiding pressurized greenhouse gases removes a common leak risk in service.

Major push toward cleaner cooling

Compact prototypes will need quiet pumps, reliable membranes, and low-voltage power electronics. Those parts already exist in other industries, which shortens the path to field tests.

Policy shifts add pressure to move faster. Phasing down hydrofluorocarbons will eventually force many sectors to adopt alternatives that are safer for people and the climate.

U.S. rules are already phasing down hydrofluorocarbons through the American Innovation and Manufacturing Act. That policy nudges manufacturers toward safer chemistries and new cooling cycles.

Standards and safety codes will also evolve with new refrigerants. Clear test protocols will help builders and regulators trust deployments.

Where this could show up first

Near-term pilots will likely target places where safety and sustainability matter as much as raw size. Vaccine fridges, portable coolers, and building heat pumps are low-hanging fruit.

If engineers solve the membrane puzzle, the same core cycle could also run in reverse to deliver efficient heating. That two-for-one trait would be welcome as electricity replaces fossil heat in many homes.

The study is published in Science.

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