Multi-Layer Radiative Cooling Structure for Daytime Solar Reflection
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Solution Overview
Problem
Daytime radiative cooling is challenging due to solar radiation heating, which complicates the achievement of cooling below ambient air temperatures, especially in buildings exposed to direct sunlight.
Innovation Solution
A radiative cooling apparatus comprising a multi-layer stack of materials that reflect solar spectrum radiation while emitting thermally-generated electromagnetic emissions in mid-IR wavelengths, allowing for cooling even under direct sunlight by utilizing the natural transparency window in the Earth's atmosphere.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a device is exposed to the sky for radiative cooling, then cooling below ambient air temperature can be achieved at night, but during daytime the device is heated by solar radiation making cooling difficult
Solution Approach 1:
The device spectrum is segmented into two distinct regions: solar reflection band (0.3-2.5 micrometers) and thermal emission band (8-13 micrometers atmospheric transparency window). The material structure is divided into multiple layers with different optical properties to independently control these spectral regions, allowing simultaneous solar reflection and thermal emission.
Solution Approach 2:
Different portions of the device have different optical properties tailored to specific wavelength ranges. The material composition and structure are locally optimized to reflect solar wavelengths while maintaining high emissivity in the mid-IR atmospheric window, creating spatially varying optical characteristics across the device spectrum.
Solution Approach 3:
The device uses composite material structures combining multiple layers with different optical properties. This includes dielectric layers, metallic layers, and photonic crystal structures that work together to achieve broadband solar reflection while maintaining high emissivity in the 8-13 micrometer atmospheric transparency window.
2Loss of energy
If conventional radiative cooling materials are used, then thermal emission can be achieved, but solar radiation is absorbed reducing cooling effectiveness during daytime
Solution Approach 1:
The device converts the harmful solar radiation that would normally be absorbed into a beneficial reflection, while simultaneously using the same material structure to enhance thermal emission in the atmospheric window. The photonic crystal structure transforms solar heating into a cooling mechanism by reflecting solar wavelengths and directing thermal emission through the atmospheric transparency window.
Solution Approach 2:
The material optical parameters are precisely engineered to change across different wavelength ranges. The emissivity and reflectivity parameters are optimized independently for solar wavelengths (high reflection) and thermal wavelengths (high emissivity), creating a dual-function material system that manages both solar heating and thermal cooling.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The apparatus effectively cools objects to temperatures 4-5 degrees Celsius below ambient air temperature even under direct sunlight, providing a passive and energy-efficient cooling solution for buildings and other structures throughout the day.
Implementation Method 1
a solar spectrum reflecting portion configured and arranged to suppress light modes, thereby inhibiting coupling of the incoming electromagnetic radiation, of at least some wavelengths in the solar spectrum, to the object
Implementation Method 2
arrangement of a plurality of different material located at different depths along a depth dimension... multi-layer stack of alternating different material
Implementation Method 3
a thermally-emissive portion... configured and arranged to facilitate, simultaneously with the inhibiting coupling of the incoming electromagnetic radiation, thermally-generated electromagnetic emissions from the object... in mid-IR wavelengths
Implementation Method 4
radiatively emit to outer space through a transparency window in the atmosphere between 8-13 micrometer wavelength range
Data Source
AI summary
Various aspects as described herein are directed to a radiative cooling apparatuses and methods for cooling an object. As consistent with one or more embodiments, a radiative cooling apparatus includes an arrangement of a plurality of different material located at different depths along a depth dimension relative to the object. The plurality of different material includes a solar spectrum reflecting portion configured and arranged to suppress light modes, thereby inhibiting coupling of the incoming electromagnetic radiation, of at least some wavelengths in the solar spectrum, to the object at a range of angles of incidence relative to the depth dimension. Further, the plurality of material includes a thermally-emissive arrangement configured and arranged to facilitate, simultaneously with the inhibiting coupling of the incoming electromagnetic radiation, the thermally-generated electromagnetic emissions from the object at the range of angles of incidence and in mid-IR wavelengths.