Radiative Cooling Film Stack for Colored Vertical Surfaces
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Solution Overview
Problem
Existing passive radiative cooling technologies are limited in their ability to effectively cool surfaces below ambient temperature during the day, particularly when oriented vertically, due to issues with surface material properties and orientation relative to the sky.
Innovation Solution
A radiative cooling article comprising a white diffusely reflective microporous layer and a non-white color reflective mirror film, which together reflect a broad spectrum of solar radiation and emit thermal radiation in the atmospheric window, enhancing cooling performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a white diffusely reflective layer is used for passive radiative cooling, then high solar reflectivity is achieved, but the cooling performance on vertical surfaces is limited
Solution Approach 1:
The patent combines a white diffusely reflective microporous layer with a non-white color reflective mirror film to create a composite structure. The white layer provides broad-spectrum solar reflectivity while the colored mirror film enhances reflectivity at specific wavelengths, together achieving superior cooling performance on vertical surfaces that neither layer could achieve alone.
Solution Approach 2:
The invention applies different reflective properties at different locations within the coating structure. The white microporous layer provides diffuse reflection across the solar spectrum, while the colored mirror film provides selective specular reflection at specific wavelengths, creating localized optical properties that optimize both solar reflection and thermal emission for vertical surface cooling.
2Temperature
If surface material properties are optimized for passive radiative cooling, then high emittance in infrared range is achieved, but solar reflectivity may be compromised
Solution Approach 1:
The patent divides the optical functionality into two distinct layers: the white microporous layer handles broad-spectrum solar reflection and infrared emission, while the colored mirror film handles selective wavelength reflection. This segmentation allows each layer to be optimized for its specific function without compromising the other, maintaining high solar reflectivity while achieving the required infrared emittance for radiative cooling.
Solution Approach 2:
The invention changes the optical parameters of the coating by combining materials with different reflectivity and emittance characteristics. The white layer provides high reflectivity across the solar spectrum (0.3-2.5 micrometers), while the colored mirror film adjusts the reflectivity profile at specific wavelengths, together achieving the dual requirement of high solar reflectivity and high infrared emittance (8-13 micrometers) needed for effective passive 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 combination achieves passive radiative cooling to below ambient temperature under direct sunlight, with high reflectivity and emissivity, suitable for commercial graphics and vehicle applications.
Implementation Method 1
a white diffusely reflective microporous layer that has a solar weighted reflectivity at normal incidence of electromagnetic radiation over a majority of wavelengths in a range of 350 nanometers (nm) to 2500 nm of 0.8 or greater
Implementation Method 2
a non-white color reflective mirror film having a plurality of first optical layers and a plurality of second optical layers... the non-white color reflective film reflects a wavelength bandwidth of at least 30 nm within a wavelength range of 350 nm to 700 nm
Implementation Method 3
For cooling surfaces below air temperature by passive radiative cooling, the surface may have high emittance in the infrared wavelength range of 8 to 13 micrometers
Implementation Method 4
a white diffusely reflective microporous layer... having a solar weighted reflectivity at normal incidence of electromagnetic radiation over a majority of wavelengths in a range of 350 nanometers (nm) to 2500 nm of 0.8 or greater
Data Source
AI summary
The present disclosure provides a radiative cooling article including a white diffusely reflective microporous layer and a non-white color reflective mirror film having first and second optical layers. The white diffusely reflective microporous layer has a solar weighted reflectivity at normal incidence of electromagnetic radiation over a majority of wavelengths in a range of 350 nanometers (nm) to 2500 nm of 0.8 or greater, 0.85, 0.9, or 0.95 or greater. The non-white color reflective film is disposed adjacent to a major surface of the white diffusely reflective microporous layer and the non-white color reflective film reflects a wavelength bandwidth of at least 30 nm within a wavelength range of 350 nm to 700 nm. The non-white color reflective film can be tuned to reflect light of a specific color (e.g., blue light, green light, or red light). The radiative cooling article may be useful for applications including commercial graphics located outdoors (e.g., on vehicles or buildings). The present disclosure further provides a composite cooling article including the radiative cooling article attached to a vehicle or a trailer. Also, the present disclosure provides a multi-surface passive cooling article including first and second elements in which at least one of the elements includes the radiative cooling article.