Retroreflective Optical Body for Window Heat Island Mitigation
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Solution Overview
Problem
Existing window coatings that reflect near-infrared light to reduce heat gain either specularly reflect sunlight, causing local temperature rises and the heat island effect, or absorb light, leading to thermal stress and poor weatherability, making them unsuitable for high-rise buildings.
Innovation Solution
An optical body with a wavelength-selective reflecting layer formed on a concave-convex surface created by arraying asymmetrical triangular pillars, which directionally reflects light in a particular wavelength band while allowing other wavelengths to pass through, reducing heat absorption and improving upward reflectance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a wavelength selective reflecting layer is formed on a flat window glass to reflect near infrared light, then the thermal shielding ability is improved, but the reflected light causes local temperature rise and heat island effect
Solution Approach 1:
The patent applies asymmetry by forming the wavelength selective reflecting layer on a corner cube structure with three mutually orthogonal reflective surfaces instead of a flat surface. This asymmetric three-dimensional geometry enables the light to be reflected back toward its source direction rather than specularly forward, preventing the heat island effect while maintaining thermal shielding ability.
Solution Approach 2:
The corner cube structure utilizes curved or angled surfaces to redirect light. The three orthogonal reflective surfaces of the corner cube create a retroreflective effect that sends light back toward its origin, converting the harmful specular reflection into a beneficial retroreflection that prevents local temperature rise.
2Temperature
If an optical multilayer film is used as a reflecting layer on window glass, then the near infrared reflectance is improved, but the structure becomes complex and costly
Solution Approach 1:
The patent changes the geometric parameter of the substrate from a flat two-dimensional surface to a three-dimensional corner cube structure. This parameter change allows the use of simpler, single-layer metallic reflective films instead of complex multi-layer optical films, reducing manufacturing complexity while achieving the same near infrared reflectance.
Solution Approach 2:
The invention creates a composite structure by combining a corner cube geometric form with a metallic reflective layer. This composite approach achieves wavelength-selective reflection through the geometric configuration rather than requiring complex material layering, simplifying the overall structure.
3Temperature
If a corner cube structure is used for retroreflection, then the upward reflection performance is improved, but the number of reflections increases heat absorption
Solution Approach 1:
The patent applies local quality by making the wavelength selective reflecting layer wavelength-dependent. The layer is designed to be highly reflective only in the near infrared range (where heat absorption occurs) while remaining transparent in the visible range. This allows the corner cube to provide retroreflection for thermal radiation while minimizing unnecessary heat absorption across all wavelengths.
Solution Approach 2:
The wavelength selective reflecting layer provides partial reflection only where needed (in the near infrared range) rather than reflecting all wavelengths. This partial action approach maintains upward reflection performance for thermal shielding while avoiding excessive heat absorption that would occur with broadband reflection.
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
This solution effectively reduces heat generation and improves energy efficiency by minimizing light absorption, while maintaining high upward reflectance and transparency, thus addressing the limitations of existing window coatings.
Implementation Method 1
a wavelength selective reflecting layer which selectively reflects light in a particular wavelength band
Implementation Method 2
selectively reflecting light in a particular wavelength band while allowing passage of light other than the particular wavelength band therethrough
Implementation Method 3
incident light is directionally reflected by the wavelength selective reflecting layer
Implementation Method 4
The optical body can retro-reflectively reflect the incident light by reflecting the incident light three times with the wavelength selective reflecting layer
Implementation Method 5
the wavelength selective reflecting layer absorbs light in amount about three times that absorbed by a flat plate and an amount of generated heat increases
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3B
AI summary
An optical body includes a first optical layer having a concave-convex surface, a wavelength selective reflecting layer formed on the concave-convex surface, and a second optical layer formed on the wavelength selective reflecting layer and embedding the concave-convex surface. The wavelength selective reflecting layer selectively directionally reflects light in a particular wavelength band while transmitting light other than the particular wavelength band therethrough. The concave-convex surface is made up of a plurality of triangular pillars arrayed in a one-dimensional pattern, and the triangular pillar has an apex angle α and a slope angle β, the apex angle α and the slope angle β satisfying a predetermined relationship.