Currently, air conditioning systems consume about 10% of the world’s electricity. According to expert forecasts, this figure could more than triple by the middle of the 21st century if the current rate of climate control technology adoption continues.
The principles of passive cooling have been known to humanity for centuries. In ancient Persia, badgirs—special towers that captured flows of cool air and directed them into buildings—were used. In some designs, the air passed over underground water channels, which helped further lower temperatures through evaporation.
Modern researchers propose using special coatings, glass, films, and gels to cool buildings. These materials can reflect solar radiation and dissipate excess heat through the atmospheric window—a range of infrared radiation with wavelengths between 8 and 13 micrometers.
Coatings containing microspheres of silicon and aluminum oxides can reflect up to 97% of solar energy. As a result, the surface temperature drops by more than 5 degrees Celsius.
Another promising direction involves the use of hydrogels. These materials can absorb moisture from the air at night and release it through evaporation during the day, cooling the surface. Applying such coatings to roofs and building facades can reduce indoor heat buildup and lessen reliance on air conditioners.
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