Solar Control Coating Structure for High SHGC Window Insulation
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Solution Overview
Problem
Conventional solar control coatings provide low solar heat gain coefficients (SHGC) that are not suitable for northern climates where trapping solar heat inside buildings during winter months is desirable, while maintaining low heat loss.
Innovation Solution
A coating system with a high SHGC and low overall heat transfer coefficient (U-value) is achieved through a layered structure comprising a dielectric layer, metallic layer, primer layer, and overcoat, optimized for architectural transparencies, allowing for efficient solar heat retention and reduced heat loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional solar control coatings are used to block solar radiation, then the solar heat gain coefficient (SHGC) is reduced, but the overall heat transfer coefficient (U-value) remains high
Solution Approach 1:
The coating is divided into multiple functional layers: a first dielectric layer (zinc oxide and zinc stannate) for solar heat rejection, a metallic layer (silver) for infrared reflection, and a second dielectric layer for additional thermal control. This segmentation allows each layer to target specific wavelengths and mechanisms of heat transfer, achieving both low SHGC and low U-value simultaneously
Solution Approach 2:
The coating combines multiple materials with complementary properties: zinc oxide and zinc stannate dielectric layers for solar radiation control, silver metallic layer for infrared reflection, and titanium dioxide overcoat for durability and UV protection. This composite structure enables the coating to address both solar heat gain and conductive heat loss through different physical mechanisms
2Loss of energy
If a low SHGC coating is used to block solar heat, then cooling load is reduced in summer, but heat trapping ability is lost in winter
Solution Approach 1:
The coating's optical properties are optimized to dynamically respond to different solar angles and intensities throughout the year. The multi-layer interference structure creates wavelength-selective transmission that naturally adapts to seasonal variations in solar spectrum, providing high solar rejection when needed while maintaining visible light transmission for winter sunlight utilization
Solution Approach 2:
Different layers of the coating are optimized for specific functions: the zinc oxide and zinc stannate layers target solar infrared radiation, the silver layer targets thermal infrared, and the titanium dioxide layer targets ultraviolet. This local optimization of each layer's properties enables the overall coating to achieve both cooling and heating benefits across different seasons
3Reliability
If a metallic layer is added to reduce U-value, then heat loss is reduced, but the solar heat gain coefficient may increase
Solution Approach 1:
The metallic silver layer is extracted and positioned at a specific depth within the multi-layer structure, surrounded by dielectric layers with carefully controlled thicknesses. This positioning allows the metallic layer to reflect infrared radiation effectively while the dielectric layers above and below it create optical interference that blocks solar radiation, preventing the metallic layer from directly increasing solar heat gain
Solution Approach 2:
The dielectric layers (zinc oxide, zinc stannate, and titanium dioxide) act as intermediary layers between the metallic silver layer and the external environment. These intermediaries control the optical paths of incoming solar radiation, preventing direct interaction with the metallic layer while still allowing the metallic layer to perform its infrared reflection function for heat retention
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 coating system effectively traps solar heat and reduces heat loss, enhancing energy efficiency in northern climates by providing a SHGC of greater than or equal to 0.6 and a U-value of less than or equal to 0.35, optimizing thermal performance for buildings.
Implementation Method 1
The coating blocks or filter selected ranges of electromagnetic radiation, such as in the range of solar infrared or solar ultraviolet radiation
Implementation Method 2
absorbed and subsequently released inwardly
Implementation Method 3
The metallic layer having a thickness less than 8 nm... provides a low emissivity to give a low U-value
Data Source
AI summary
A coating provides a high solar heat gain coefficient (SHGC) and a low overall heat transfer coefficient (U-value) to trap and retain solar heat. The coating and coated article are particularly useful for use in architectural transparencies in northern climates. The coating includes a first dielectric layer; a continuous metallic layer formed over at least a portion of the first dielectric layer, the metallic layer having a thickness less than 8 nm; a primer layer formed over at least a portion of the metallic layer; a second dielectric layer formed over at least a portion of the primer layer; and an overcoat formed over at least a portion of the second dielectric layer. When used on a No. 3 surface of a reference IGU, the coating provides a SHGC of greater than or equal to 0.6 and a U-value of less than or equal to 0.35.