Sustainable air conditioner without electricity can harness solar energy to reduce temperatures in hot weather

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Scientists at KAUST developed a simple cooling system based on solar energy and the cooling effect of the evaporation of salt water that could be used for refrigeration in hot regions with limited access to water. electricity. Credit: © 2021 KAUST; Veronique moraru

Powerful sunlight powers the passive cooling device

A simple cooling system powered by capturing passive solar energy could provide low-cost food refrigeration and living space cooling for impoverished communities without access to the electricity grid. The system, which has no electrical components, harnesses the powerful cooling effect that occurs when certain salts are dissolved in water. After each cooling cycle, the system uses solar energy to evaporate the water and regenerate the salt, ready for reuse.

“Hot regions have high levels of solar energy, so it would be very interesting to use this solar energy for cooling,” says Wenbin Wang, post-doctoral fellow in Peng Wang’s lab. In many parts of the world, the need for cooling is greater due to climate change, but not all communities have access to electricity for air conditioning and refrigeration. “We conceptualized an off-grid solar energy conversion and storage design for green and inexpensive cooling,” says Professor Wang.

Passive cooling system

The cooling system designed by KAUST engineers could be used to cool household rooms. Credit: © 2021 KAUST; Wenbin Wang

The team designed a two-stage cooling and regeneration system, with the cooling stage based on the fact that dissolving some common salts in water absorbs energy, which quickly cools the water. . After comparing a range of salts, ammonium nitrate (NH4NO3) proved to be the most efficient, with more than four times the cooling power of its closest competitor, ammonium chloride (NH4Cl). The exceptional cooling power of ammonium nitrate salt can be attributed to its high solubility. “NH4NO3the solubility of s was 208 grams per 100 grams of water, while other salts were generally less than 100 grams, ”explains Wenbin. “The other advantage of this salt is that it is very cheap and already widely used as a fertilizer,” he adds.

The system has good potential for food storage applications, the team showed. When the salt has been gradually dissolved in the water in a metal cup placed inside a polystyrene foam box, the temperature of the mug rose from room temperature to about 3.6 degrees Celsius and stayed below 15 degrees Celsius for more than 15 hours.

Once the saline solution reached room temperature, the team used solar energy to evaporate the water using a custom cup-shaped 3D solar regenerator. The mug has been made from a material designed to absorb as much of the solar spectrum as possible. As the water evaporates, the NH4NO3 crystals have grown on the outer wall of the cup. “Crystallized salt can be collected automatically as the salt falls due to gravity,” says Wenbin.

Once collected, salt effectively represents a stored form of solar energy, ready to be reused for cooling when needed.

Reference: “Solar Energy Conversion and Storage for Cooling” by Wenbin Wang, Yusuf Shi, Chenlin Zhang, Renyuan Li, Mengchun Wu, Sifei Zhuo Sara Aleida and Peng Wang, September 1, 2021, Energy and environmental sciences.
DOI: 10.1039 / D1EE01688A

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