Radiative Cooling of Any Sky-Facing Surface

John Roehling | 21-LW-006

Project Overview

The number of air-conditioning units worldwide is expected to triple by midcentury. With temperatures increasing and heat waves occurring more frequently due to climate change, the possibility of creating electricity-free, 24-hr cooling is increasingly attractive. In this project, we created aerogels from common salts that effectively acted like a one-way valve for heat, allowing an underlying surface to cool to sub-ambient temperatures by losing heat to the sky. NaCl and KCl are inexpensive, naturally abundant, and highly IR-transparent materials. By freeze drying flash-frozen solutions of these salts and optimizing their microstructure, NaCl+KCl aerogels were fabricated that scattered visible light, transmitted infrared radiation, and provided thermal insulation to a sky-facing surface. After packaging the aerogel into a mechanical support, these aerogels were shown to cool a surface 24 hours a day, even while the sun was shining. This work demonstrated an affordable, electricity-free cooling technology with great potential to be manufactured on a large scale for practical applications, such as supplemental cooling for buildings or remote refrigeration. It can also be used with a variety of underlying materials and can improve the performance of many already proven radiative cooling technologies.

Mission Impact

This work continues the Laboratory's core competency in advanced materials and manufacturing. Materials to provide electricity-free cooling have importance for the lab's mission in energy security and climate resilience. This project leverages the investments made in advanced manufacturing and creates new applications for aerogels. The patent applications will hopefully provide future industrial partnerships.

Publications, Presentations, and Patents

Roehling, J., et al. "Infrared Transparent Foam Composite for Deep Sub-Ambient Cooling of Virtually Any Surface." U.S. Patent No. 17/935.396. September 26, 2022.