An electricity-free cooling system that could be deployed in data centers has been prototyped by researchers in Germany and Japan.

The team from the Karlsruhe Institute of Technology (KIT) and the University of Tsukuba has developed the solid-state cooling system, which uses two ultra-thin shape-memory films to convert thermal energy into mechanical work and cooling power.

According to researchers, the prototype is thought to be the first system of its kind to achieve this without an electric motor, and could open the door for more efficient data center cooling in the future. Cooling systems can account for up to 40 percent of a data center’s power bill.

Elastocaloric solid-state cooling is an alternative to traditional cooling systems that utilizes semiconductor materials known as shape-memory alloys. When a mechanical load is applied to the chosen material, its crystal structure changes, making it heat up. Removing the mechanical load allows the material to snap back into its original structure and cool down. Past versions of this type of system have required an electric motor to generate the force required to get the process going, meaning it couldn’t directly use waste heat.

But the new research, published in the journal Nature Energy, demonstrates an alternative. It couples two ultra-thin nickel-titanium films that have complementary functions. The first film starts to shrink when heated by a server or other piece of electronic equipment, thereby converting thermal energy directly into mechanical work – without the help of an electric motor.

This motion immediately transfers to the second film, where cyclic loading and unloading bring about reversible alterations in the crystal structure that generate cold that can be used for cooling. The heat replaces the electrically driven actuator, previously used to drive elastocaloric cooling systems.

“The crucial innovation is that we combine two complementary functions of shape memory alloys, with one film converting heat into mechanical work and the other film converting this work into cold,” said Dr. Jingyuan Xu, who leads the young investigator group of the ZEco Thermal Lab at KIT’s Institute of Microstructure Technology (IMT). “This way, we’re establishing a new approach to drive solid-state cooling, thereby opening up exciting possibilities for the use of waste heat and solar energy.”

At an actuator temperature of 86°C (186°F), the prototype system achieved a temperature difference of 4°C (39.°F) on the component level. Data center chips typically reach internal temperatures of 60°C–85°C (140°F–185°F), with conventional air and liquid cooling systems capable of removing anywhere between 10–20°C (50-100°F) of heat, so there is still some work to do to make solid-state systems as effective as those currently on the market, but the researchers say their experiments prove the feasibility of the concept for the first time.

“We believe that this is only the beginning,” said Dr. Xu. “By scaling up this technology, we want to develop compact cooling systems that leverage abundantly available heat sources for sustainable cooling.”

Some vendors are already experimenting with solid-state cooling. In May, UK-based Barocal raised $10 million to commercialize its system, aimed at the data center cooling market.