Design of Double‐Sided Optical Coatings for Space Cooling Through Vertical Windows

Passive radiative cooling is a promising energy‐saving strategy for space cooling. Dual‐sided thermal emitters offer efficient heat removal from enclosed spaces; however, existing studies predominantly focus on rooftop applications, with limited attention to vertical surfaces, such as walls and windows. Here, a dual‐sided radiative cooling glass (DSRCG) tailored for vertical applications proposed, enhancing enclosure cooling. The DSRCG incorporates multilayer epsilon‐near‐zero materials, including Al 2 O 3 and Si 3 N 4 , layered on a double‐sided indium‐tin‐oxide‐coated glass. The outward side of the DSRCG exhibits angular‐selective emission for efficient heat dissipation, while the inward side minimizes thermal radiation into enclosures. The visibly transparent layers enable a visible transmittance exceeding 72%. The simulation results demonstrate that the DSRCG reduces heat transfer to enclosures by 15 W m −2 compared with the conventional glass (C‐glass) at ambient temperatures above 30 °C. These findings highlight the DSRCG's potential as an energy‐saving window for reducing space‐cooling energy usage.