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A research team from the University of Notre Dame has developed a groundbreaking window coating capable of cooling a space irrespective of the angle at which the sun’s rays strike the glass. This technology, which hinges on the significance of the sun’s angle when passing through the window, represents a substantial innovation compared to existing market solutions.
Why is the angle at which the sun’s rays fall on the window important? The variability of the angle between direct sunlight and the window’s normal vector, particularly pronounced during midday hours when the sun is highest and temperatures peak, poses a challenge for traditional filters designed to function only with direct sunlight.
Tengfei Luo, the lead author of the study, elucidated that their coating remains effective and functional regardless of changes in the sun’s position throughout the day. The coating comprises layers of silicon dioxide, aluminium oxide, and titanium dioxide applied to a glass substrate, supplemented by an extremely thin layer of silicone polymer that reflects heat radiation, thereby enhancing cooling.
Silicone polymers, renowned for their flexibility and durability, effectively dissipate heat away from the source, preventing overheating.
The challenge in developing this coating lay in selecting the optimal combination of layers to enable efficient reflection of the sun’s rays at various angles. Luo observed that owing to the myriad possible combinations, the trial-and-error method proved impractical.
By employing quantum cooling to identify the ideal combination, the researchers experimentally confirmed the optical characteristics and the photonic structure’s ability to reduce temperature rise within the room when combined with a thermal radiation layer. Through simulations, they demonstrated that this coating can lower temperatures by 5.4°C to 7.2°C, resulting in annual energy savings of approximately 97.5MJ/m2.
Further tests with horizontally positioned windows showcased the outstanding cooling performance of the photonic structure, reducing temperatures by up to 7.2°C. Luo likened the coating to polarised sunglasses: it diminishes light intensity without compromising visibility, even as the viewing angle changes. This characteristic renders the coating ideal not only for buildings but also for vehicles.
The research concludes that this window coating could find widespread application and make a significant contribution to energy efficiency in cities across the United States and worldwide, particularly in areas with tropical climates.