New breakthrough in zero-energy technology to stay cool without electricity

Imagine a system that can provide cooling for building air conditioning, food refrigeration and many other applications…all without the need for electricity.

It may sound like science fiction, but thanks to the efforts of MIT researchers, an innovative new passive cooling system could one day replace several traditional technologies, offering an alternative that requires no power input and requires only the right amount of Water can function.

By combining principles involving three different cooling methods (radiative, evaporative, and adiabatic cooling), the team developed a new technique that they say can reduce room temperature by as much as 19 degrees Fahrenheit from room temperature. The system, which looks similar to existing solar panels, can safely store food in most conditions and even triple in extreme dry conditions.

While each of the three cooling methods employed in the recent MIT study has been successful, it was the team’s unique approach to combining them that resulted in the new passive zero-energy technology.

“This technique combines some of the advantages of previous techniques, such as evaporative cooling and radiative cooling,” said Zhengmao Lv, an MIT postdoc whose team is in Cell Reports Physical ScienceLu says these combined technologies can significantly extend the shelf life of food, even under high humidity conditions that typically shorten the time it takes for food to be safely eaten.

Zhengmao Lu, a postdoctoral fellow in MIT’s Department of Materials Science and Engineering, is the lead author of the study (Credit: Credit: MIT/Zhengmao Lu).

In addition to using it as a stand-alone zero-power technology for cooling systems, Lu believes the new technology he and his colleagues at MIT has developed could complement existing cooling systems by reducing the amount of electricity required to operate. One of the most obvious applications is reducing the amount of electricity needed to power air conditioning systems in hot climates.

“By lowering the condenser temperature, you can effectively increase the air conditioning efficiency,” Lu said in a recent statement, adding that this pairing of existing and new technologies can “potentially save energy.” The same applies to humid regions, Lu said, where even the best radiative cooling techniques often struggle to maintain peak performance.

The MIT team’s design relies on the structure of three layers of materials that cool the water and heat passing through them. The top layer is aerogel, a sponge-like material composed of polyethylene filled with small air-filled bubbles or cavities. One of the unique advantages of aerogels is that they allow water vapor to pass through while still acting as excellent insulators. They also allow the passage of infrared radiation, which is essential for releasing heat upwards into the air, as opposed to how radiant air conditioning systems release hot air due to the power required to run them.

Zero Energy Technology
Above: Schematic of the cooling system designed by the MIT team (Image credit: Zhengmao Lu, et al, Cell Reports Physical Science).

The second layer is a hydrogel, similar to the aerogel layer above it, although its cavity is filled with water, which aids the evaporation needed for cooling. Finally, a third layer with a reflective surface helps prevent sunlight that might have passed through the first two layers from being absorbed, reflecting it back to the aerogel and hydrogel layers above it.

While electricity is not required, moderate amounts of water—perhaps as little as twice a week—are required in particularly dry areas for evaporation to occur. Wetter areas may require less maintenance and in most cases only add water once a month.


The integration of all three cooling methods into an innovative passive cooling system is considered a truly novel approach by the team, Lu said. Even during an early test phase involving a small version of the new combined technology in the MIT rooftop area, the team managed to demonstrate the ability to cool close to 19 degrees.

The team believes the new technology could one day help supply cooling systems in many parts of the world where electricity, water and other resources are extremely scarce.

The team’s study, titled “Significantly enhanced sub-ambient passive cooling via evaporation, radiation, and insulation,” was recently published in Cell Reports Physical Science and can be read online.

Micah Hanks is the editor-in-chief and co-founder of The Debrief. Follow his work on and Twitter: @MicahHanks.

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