Cooling mechanism based on our SkyActive nanoparticles

RARE: a radiative cooling paint

Wideband reflection on solar spectrum

External surfaces are heated up due to the absorption of solar irradiation. RARE reflects more than 95% of this energy over the full solar spectrum from 0.3 µm to 3 µm.

On the market, other anti heating paint only focus on infrared reflection near the 1 µm wavelength, thus, reflecting less sunlight. Moreover, using low-quality ingredients reduce the reflection to below 90%.

Radiative in the atmosphere transparent window

Earth atmosphere is transparent in the 8-14 µm window. Radiations in this wavelength range are not absorbed and travel to the outer space. RARE has the proper materials and structures that emit strongly in the 8-14 µm, more than 92%, thus directly exchange heat with the universe, and cools itself. With about 100 W additional cooling power per m2, RARE always approximate the ambient.

On the market, there is no other similar product. Without the need of energy, there is no other product that as cooled as RARE.

Solar spectrum (blue): With a surface temperature of 5000 C, the Sun emits strongly in the visible spectrum 0.3-0.7 µm and in the near-infrared 0.7-2.5 µm, as shown in the blue shading. In the summer, this heat can reach 1000 W per square meter. To avoid this heat, external surfaces need to reflect at least 90% in the 0.3-3 µm.

Atmospheric transmittance spectrum (yellow): Gas molecule in the air absorb strongly in the range of 5-8 µm, corresponding to their vibrations and thermal motions. However, the 8-14 µm window is transparent. If a surface emits strongly in this range, they are off balance with the surrounding. The radiative cooling power is estimated about 100W/m2.

RARE radiative spectrum (red): RARE radiative cooling paint possess many peaks in the 8-14 µm. It radiates strongly in this range. These radiations are not absorbed in the air, and escape the Earth to the outer space. To reach the ambient temperature, RARE also reflect heat strongly in the infrared spectrum of the Sun (data not showed).

The spectrum of the Sun and of RARE

A PROTOTYPE: STEEL CABINET 2x2 M2

The steel cabinet

always stay equal or below the environment. At night when there is no Sunlight, the steel cabinet is 5 degrees colder than the air. In the daytime, the temperature inside is equal to or lower than the air (under the shade). Temperature differences compare to a steel roof without coating can reach 40 degrees C.

The temperature of the steel cabinet in 2020:

  • Red: Tole without RARE

  • Grey: Air outside (under shade)

  • Green: Air inside

  • Blue: Top surface (steel)

Temperature of tole with RARE (blue) compared to air temperature (red) in consecutive days.

June 2023, temperature in Hanoi.

July 2023, temperature in Hanoi.

August 2023, temperature in Hanoi.