Radiative cooling systems
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Solution Overview
Problem
Radiative cooling materials face durability challenges due to long-term outdoor exposure, particularly under sunlight and weathering conditions, which affects their effectiveness.
Innovation Solution
Development of materials with high thermal emissivity and ultraviolet absorption or reflection capabilities, integrated with heat exchangers and designed for durable radiative cooling systems that can maintain performance over time, including configurations for building and vehicle applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If radiative cooling materials are deployed outdoors for long-term use, then cooling effectiveness is achieved, but durability deteriorates due to sunlight and weathering exposure
Solution Approach 1:
The cooling panel is divided into multiple functional layers: a UV-resistant top layer (containing TiO2, SiO2, or ZnO particles) that protects against sunlight degradation, and a bottom radiative cooling layer that maintains high thermal emissivity in the 8-13 μm atmospheric window. This segmentation allows each layer to specialize in its function while protecting the overall system durability.
Solution Approach 2:
The patent employs composite material structures combining different materials with complementary properties. The top layer uses UV-resistant materials (TiO2, SiO2, ZnO) mixed with binders, while the bottom layer uses high-emissivity materials. This composite approach enables simultaneous UV resistance and radiative cooling performance, resolving the contradiction between durability and cooling effectiveness.
2Reliability
If materials absorb ultraviolet radiation to prevent degradation, then durability is improved, but solar heat absorption increases reducing cooling performance
Solution Approach 1:
The patent applies local quality by giving different spectral properties to different layers: the top layer is designed with high UV absorption/reflection properties for durability, while the bottom layer is optimized for high thermal emissivity in the 8-13 μm infrared range for cooling. This spatial differentiation of material properties allows UV protection without compromising radiative cooling performance.
Solution Approach 2:
The patent changes the spectral parameters of different layers to resolve the contradiction. The top layer is engineered with specific UV absorption characteristics (using TiO2, SiO2, or ZnO particles), while the bottom layer is designed with high emissivity in the atmospheric window region. This parameter optimization across different spectral ranges enables both durability and cooling effectiveness.
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 materials achieve significant cooling rates and durability, capable of maintaining temperatures below ambient air temperatures, even under harsh conditions, and can be integrated with heat exchangers for enhanced cooling performance.
Implementation Method 1
a thermal emissivity of at least 0.8 in spectral range of 5 μm to 15 μm
Implementation Method 2
The material exhibits strong ultraviolet absorption or reflection in the spectral range of 275 nm to 375 nm
Implementation Method 3
the material is capable of reflecting greater than 93% of the weighted solar spectrum from 300 nm to 4 μm in free-space wavelength
Data Source
AI summary
A material may be included in a cooling film or cooling panel to achieve cooling even under direct solar irradiation. The material includes one or more constituent materials and an outer surface configured to interact thermally with the atmosphere and with solar radiation. The material exhibits an emissivity of at least 0.8 in spectral range of 5 μm to 15 μm, an ultraviolet reflectivity of at least 0.5 in the spectral range of 275 nm to 375 nm, an ultraviolet absorptivity of at least 0.75 in the spectral range of 275 nm to 375 nm, or a combination thereof. A cooling film, or cooling panel, may be affixed to an exterior surface of a vehicle, structure, or system to provide cooling even under direct solar irradiance.