Coating with smart sub-ambient radiative cooling
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Solution Overview
Problem
Current sub-ambient daytime radiative cooling (SDRC) technologies face challenges such as high costs, environmental impact, and limited scalability due to the use of sophisticated materials and designs, which result in inadequate daytime cooling and excessive nighttime cooling, leading to thermal stress on building structures.
Innovation Solution
Development of a smart sub-ambient radiative cooling (SSRC) coating using TiO2 particles, inorganic particles, fluorescent pigment particles, and a polymer, which enhances solar reflectance and broadband emissivity, allowing for effective daytime cooling while suppressing nighttime overcooling, thus overcoming the limitations of conventional SDRC systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional TiO2-based cool roof coatings are used, then the coating is cost-effective and easy to manufacture, but the solar reflectance is only approximately 85%, which is not sufficiently high to meet the stringent requirements of sub-ambient daytime radiative cooling
Solution Approach 1:
The patent combines TiO2 particles with fluorescent pigment particles and inorganic particles to create a composite coating material. This composite structure enables the coating to achieve both high solar reflectance (ESR≥90%) and broadband infrared emissivity (≥0.90) while maintaining ease of manufacture using conventional building coating materials and processes.
2Temperature
If sophisticated photonic microstructures, noble metal mirrors, or metamaterials are used to achieve sub-ambient daytime cooling, then the cooling performance is improved, but the cost increases and environmental impact worsens due to hazardous chemical processes
Solution Approach 1:
The patent replaces expensive and environmentally harmful materials (noble metal mirrors, metamaterials, hazardous chemicals) with inexpensive, eco-friendly conventional building coating materials such as TiO2 particles, fluorescent pigments, and inorganic particles. This substitution maintains effective sub-ambient daytime cooling performance while dramatically reducing manufacturing complexity and environmental impact.
3Temperature
If existing SDRC materials are designed to reflect most sunlight to achieve daytime cooling, then daytime cooling is improved, but nighttime cooling becomes excessively strong leading to overcooling effect in cold winter
Solution Approach 1:
The patent employs broadband infrared emissivity materials that emit across the entire mid-infrared spectrum (3-50 μm) rather than only in the narrow atmospheric transparency window (8-13 μm). This broadband emission capability allows the coating to adaptively exchange heat with the sky at different wavelengths, achieving effective daytime cooling while suppressing excessive nighttime cooling and enabling heating assistance in cold winter conditions.
4Temperature
If existing SDRC designs are used, then daytime cooling is achieved, but the diurnal temperature difference is enlarged which may jeopardize the service life of building envelopes due to thermal stresses
Solution Approach 1:
The patent utilizes materials with broadband infrared emissivity characteristics that enable adaptive thermal radiation across different wavelengths and time periods. This parameter-based approach (broadband emissivity ≥0.90 across 3-50 μm) allows the coating to modulate its cooling effect, reducing the extreme diurnal temperature difference and thereby protecting building envelopes from thermal stress damage while maintaining effective daytime 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 SSRC coating achieves enhanced daytime radiative cooling of 6°C under direct sunlight and 4°C at nighttime, with a cooling power of 64.5 W/m², demonstrating a cost-effective and eco-friendly solution for large-scale building applications, reducing energy demands and thermal stress on buildings.
Implementation Method 1
daytime radiative cooling materials were designed, using various approaches, to reflect most of the sunlight such that the heat absorption from the sun is below the level of radiative cooling
Implementation Method 2
These radiative cooling materials exploit the infrared transparency window of the atmosphere, in the wavelength range of 8-13 μm, to directly transmit heat from an object at ambient temperature, through blackbody radiation, to the cold outer space which has a temperature of 3 K
Implementation Method 3
through the addition of fluorescent materials, part of the absorbed solar energy is effectively converted to fluorescence emission to yield an improved effective solar reflectance (ESR)
Data Source
AI summary
A smart sub-ambient radiative cooling composition including TiO2 particles; inorganic particles selected from the group consisting of SiO2, CaCO3, SiC, ZnO, Al2O3, ZnO, and mixtures thereof; fluorescent pigment particles; and a polymer useful for sub-ambient radiative cooling, methods of preparation, and use thereof.