Low-E Film Surface Roughness for Glazing SHGC and U-Value
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Solution Overview
Problem
Existing multiple-glazed glass units have limited ranges for Solar Heat Gain Coefficient (SHGC) values, which restrict their ability to maintain comfortable indoor environments and reduce energy consumption throughout the year, while also having a high heat transmission coefficient (U-value).
Innovation Solution
A multiple-glazed glass unit design featuring two glass panes with low-emissivity (Low-E) films on both principal surfaces, where one film has an arithmetic average surface roughness of 14 nm or less, and a specific multilayer structure including metal, dielectric, and sacrificial layers to enhance heat shielding and insulating properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If low-emissivity films are formed on both principal surfaces of glass panes to improve heat shielding properties and reduce U-value, then heat insulation performance is improved, but the range of SHGC values is limited
Solution Approach 1:
The patent applies different surface roughness characteristics to different Low-E films: the first Low-E film (facing outdoor space) has Ra > 14 nm for scattering solar radiation and controlling SHGC, while the second Low-E film (facing indoor space) has Ra ≤ 14 nm for maintaining optical clarity and heat reflection. This local differentiation allows independent optimization of heat shielding and solar control properties
Solution Approach 2:
The patent changes the surface roughness parameter (Ra value) of Low-E films to achieve different optical functions. By controlling the arithmetic average surface roughness to be greater than 14 nm for the outdoor-facing film and 14 nm or less for the indoor-facing film, the patent expands the achievable SHGC range while maintaining low U-value through the dual Low-E film configuration
2Loss of energy
If multiple Low-E films are formed on glass panes to achieve low U-value, then heat insulation is improved, but manufacturing complexity increases
Solution Approach 1:
The patent segments the Low-E film functionality into two distinct films with different surface roughness characteristics: the first Low-E film (Ra > 14 nm) primarily handles solar radiation scattering and SHGC control, while the second Low-E film (Ra ≤ 14 nm) focuses on heat reflection and optical clarity. This segmentation allows each film to be optimized for its specific function, simplifying the overall design compared to attempting to achieve all functions in a single complex film structure
Solution Approach 2:
The patent uses composite film structures where each Low-E film comprises multiple layers including metal layers (silver, aluminum), dielectric layers (oxides, nitrides), and organic-inorganic hybrid layers. These composite materials provide both the low-emissivity property for heat insulation and the controlled surface roughness for optical management, achieving low U-value without excessive structural complexity
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 design achieves a higher SHGC value and lower U-value, improving indoor comfort and reducing energy requirements year-round, while maintaining good decontamination properties and durability.
Implementation Method 1
a second low-emissivity film is formed on the other principal surface of the one glass pane, the other principal surface facing the indoor space, and the second low-emissivity film formed on the other principal surface facing the indoor space has an arithmetic average surface roughness Ra of 14 nm or less
Implementation Method 2
a specific multilayer structure including metal, dielectric, and sacrificial layers to enhance heat shielding and insulating properties
Implementation Method 3
a multiple-glazed glass unit including a first glass pane and a second glass pane which are opposed to each other across a gap layer to be spaced at a predetermined distance from each other
Data Source
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AI summary
A multiple-glazed glass unit of the present invention is adapted to separate an indoor space and an outdoor space and includes a pair of glass panes opposed across a gap layer to be spaced at a predetermined distance from each other. Low-emissivity (Low-E) films are formed on both principal surfaces of one of the pair of glass panes that is located closer to the indoor space. The low-emissivity film formed on one of the two principal surfaces that faces the indoor space has an arithmetic average surface roughness Ra of 14 nm or less. This multiple-glazed glass unit is configurable to have a higher SHGC value ever than before as well as keeping a low U-value.