A recent study published in Advanced Photonics Research introduces a dual-sided radiative cooling glass (DSRCG) designed for vertical applications like windows. This innovative technology aims to enhance energy efficiency and provide a sustainable cooling solution to address global energy consumption and climate challenges.
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Advancements in Radiative Cooling Technology
The growing concern over climate change and energy consumption has driven the development of passive cooling technologies.
Traditional cooling systems account for approximately 20 % of global energy use, contributing significantly to air pollution and fossil fuel depletion. In contrast, passive radiative cooling enables heat dissipation without mechanical systems or carbon emissions by emitting thermal radiation in the mid-infrared range, allowing heat to escape into space.
While passive cooling has been explored in roofing, solar panels, electronics, and clothing, most research has focused on horizontal surfaces. Vertical surfaces like windows and walls have received less attention, despite their potential impact on indoor temperature regulation.
Previous studies on dual-sided thermal emitters, or Janus emitters, have shown promise in improving heat removal, but urban environments present challenges due to obstructed heat dissipation. This study proposes a novel radiative cooling glass tailored for efficient vertical performance.
Introducing the Dual-Sided Radiative Cooling Glass
Researchers designed and validated the DSRCG, which consists of a double-sided indium tin oxide (ITO)-coated glass substrate layered with epsilon-near-zero (ENZ) materials, mainly silicon nitride (Si3N4) and aluminum oxide (Al2O3).
The outward-facing side features angular-selective thermal emission for effective heat dissipation, while the inward-facing side minimizes thermal radiation into enclosed spaces by acting as a thermal reflector. This configuration is particularly useful in urban areas, where buildings are closely packed, limiting skyward heat dissipation.
To evaluate its performance, the researchers developed a theoretical model that accounted for nearby objects, enclosure conditions, and convection effects. Advanced simulation tools, including DiffractMOD for optical property calculations and MATLAB for thermal simulations, were used to analyze the DSRCG’s performance under typical summer conditions.
The study examined the glass’s emissivity properties while maintaining a high visible transmittance of approximately 72 %. The material configuration was also designed to generate Berreman modes, which enhance directional thermal emission.
Key Findings: How This Glass Enhances Cooling
Simulations showed that the DSRCG reduces heat flux into indoor spaces by over 16 W/m2 compared to conventional soda-lime glass at temperatures above 20 °C. It maintained strong cooling performance even in high-temperature conditions (>30 °C) and windy environments (>10 m/s), making it well-suited for urban settings with limited airflow.
The DSRCG’s dual functionality—directing heat outward while reducing heat gain inside—improves its energy-saving potential. It maintains high visible light transmission (72 %), making it suitable for windows without blocking natural light.
The study also quantified the DSRCG’s potential impact on energy use, estimating cooling energy savings between 28.9 % and 40.5 % per household. In an average apartment (75.5 m2 floor area), this translates to annual energy savings of approximately 355.3 kWh. These findings suggest that integrating DSRCG into building design could significantly reduce reliance on air conditioning, particularly in hot climates.
Practical Applications and Future Potential
The DSRCG has promising applications across residential, commercial, and industrial settings. It can be integrated into urban infrastructure, office buildings, and specialized environments such as cold storage facilities, where minimizing heat transfer is critical. By reducing cooling loads, this advanced glass can enhance air conditioning efficiency, lower energy costs, and improve sustainability in building design.
What’s Next for This Cooling Innovation?
The development of DSRCG marks a significant step in passive cooling technology, offering a practical way to improve building energy efficiency. As cities face rising temperatures, adopting this glass in architecture could play a key role in reducing cooling energy demand.
Future research should focus on optimizing directional thermal emission, fabricating prototypes, and conducting real-world tests to validate theoretical findings. Refining material composition and surface structure could further improve performance, while expanding research into various building types will help determine its adaptability.
With continued advancements, DSRCG technology could become a widely used solution for sustainable cooling in modern architecture.
How Are Material Advancements Shaping Energy-Efficient Cooling?
Journal Reference
Kwak, H., Kim, D, H., Song, Y, M. (2025). Design of Double-Sided Optical Coatings for Space Cooling Through Vertical Windows. Advanced Photonics Research. DOI: 10.1002/adpr.202400205, https://advanced.onlinelibrary.wiley.com/doi/10.1002/adpr.202400205
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