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 with a solar spectrum reflecting portion and a thermally-emissive portion, integrated along a depth dimension, which suppresses solar radiation absorption and facilitates thermal emission in mid-IR wavelengths, allowing for effective cooling even under direct sunlight.
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 absorbs solar radiation which prevents effective cooling
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). By separating the functional requirements for solar wavelength and thermal wavelength, the device can simultaneously reflect solar radiation and emit thermal radiation through the atmospheric window, achieving daytime cooling below ambient temperature
Solution Approach 2:
The device exhibits different optical properties at different wavelengths: high reflectivity in the solar spectrum region and high emissivity in the thermal infrared region. This wavelength-dependent local quality allows the device to selectively interact with different parts of the electromagnetic spectrum, reflecting harmful solar radiation while efficiently emitting thermal energy to space
2Ease of manufacture
If conventional materials are used for radiative cooling, then simple construction is achieved, but the ability to simultaneously reflect solar radiation and emit thermal radiation is insufficient
Solution Approach 1:
The device employs a composite structure combining multiple materials with complementary optical properties: silicon monoxide layer for strong thermal emission in the 8-13 micrometer atmospheric window, and fluoropolymer coating for broad-spectrum solar reflection. This composite material approach achieves the dual functionality of solar reflection and thermal emission that single materials cannot provide, enabling reliable daytime radiative 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 achieves cooling up to 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
a thermally-emissive portion that includes a portion of the different material that are arranged in the depth dimension, and configured and arranged to facilitate, simultaneously with the inhibiting coupling of the incoming electromagnetic radiation, thermally-generated electromagnetic emissions from the object at the range of angles of incidence and in mid-IR wavelengths
Implementation Method 3
Radiative cooling exposes a device to the sky to 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.