In the realm of urban development, where approximately 40% of the world’s energy consumption is attributed to buildings, the infiltration of heat through windows has emerged as a significant contributor to wasted heating and cooling energy. A groundbreaking ‘smart window’ technology has been engineered by a team of researchers at KAIST, designed not only to diminish heating and cooling energy consumption in urban structures but also to combat the prevalent issue of ‘light pollution’ in urban environments.
Pioneering Pedestrian-Friendly Smart Window Technology
Professor Hong Chul Moon and his team at KAIST’s Department of Chemical and Biomolecular Engineering have unveiled a revolutionary ‘smart window technology’ that empowers users to regulate the light and heat entering through windows based on their preferences, effectively mitigating glare from external sources.
Advanced Control with Real-time Operation
Their findings, recently published in ACS Energy Letters, shed light on the emergence of active smart window technology, enabling dynamic adjustment of light and heat through user intervention in real-time. Unlike traditional windows that passively respond to environmental changes, this cutting-edge system can be actively managed via electrical signals.
The RECM System: A Game-Changer in Window Technology
The research team’s latest innovation, the RECM (Reversible Electrodeposition and Electrochromic Mirror) system, represents a single-structured electrochromic device that offers active control over visible light transmittance and near-infrared heat.
Achieving Glare-Free Windows
By effectively addressing glare issues caused by external reflected light, a common drawback in conventional reflective smart windows, through the integration of electrochromic materials, a ‘pedestrian-friendly smart window’ suitable for urban building exteriors has been realized.
Operational Modes of the RECM System
The RECM system developed by the team functions in three distinct modes based on voltage control:
- Mode I (Transparent Mode): Ideal for allowing sunlight penetration during winter months, resembling ordinary glass in transmitting both light and heat.
- Mode II (Colored Mode): In this mode, the window adopts a deep blue hue through the formation of Prussian Blue (PB) and DHV+• chemical species, enabling privacy and controlled indoor temperature.
- Mode III (Colored and Deposition Mode): Involves the deposition of silver (Ag+) ions on the electrode surface to reflect light and heat, simultaneously absorbing reflected light to eliminate glare for pedestrians outside.
Practical Temperature Reduction and Instantaneous Response
The team demonstrated the tangible indoor temperature reduction benefits of the RECM technology through experiments conducted in a miniature model house. The results showcased a remarkable temperature drop of approximately 27.2°C when operating in Mode III, compared to traditional glass windows.
Moreover, the system’s ability to transition between states solely through electrical signals positions it as a proactive smart technology capable of swift responses tailored to seasonal, time-dependent, and user-specific needs.
Anticipating Diverse Applications
Professor Hong Chul Moon envisions a broad spectrum of applications for this innovative smart window technology, spanning from urban buildings to vehicles and trains. By surpassing the limitations of existing smart windows focused solely on visible light control, the platform presented in this study offers a comprehensive solution for active indoor thermal management and pedestrian visual safety.
More information:
Hoy Jung Jo et al, Glare-Free, Energy-Efficient Smart Windows: A Pedestrian-Friendly System with Dynamically Tunable Light and Heat Regulation, ACS Energy Letters (2025). DOI: 10.1021/acsenergylett.5c00637
