It’s been a productive snow day. Footprints and sled tracks cover the ground, and twenty-two rows of little snowmen line the backyard. But alas! The sun has numbered the miniature army’s days. Freezers could prolong their lives, but it would require ten freezers to fit all the snowmen, which would cost two thousand dollars per year… if only there were a cheaper way to protect them.
But then, a flash of hope! A factoid from physics springs to memory. “The average temperature in space is -negative two hundred and fifty-five degrees Fahrenheit! The cold of space to save the snowmen!”
Is it unreasonable? Probably. But impossible? Not at all!
The secret is radiative cooling, a strategy in which excess heat is absorbed by the sky. Instead of inputting energy to keep things cool, as a fridge does, the unwanted heat would instead be exchanged with the cold of the atmosphere. This naturally happens all the time, especially when an object such as a car or building is directly exposed to the sky on a clear night. In fact, in ancient times people living in hot desert climates like North Africa and India would capitalize on this convenient consequence of the greenhouse effect to make ice. In the evening, they would line ceramic trays with reeds and fill them with water, the sky would absorb the water’s heat all night, and by morning, the water would be frozen (Kaplan). Today the trick to harnessing radiative cooling as an economical method of refrigeration lies in finding a material that will reliably transmit heat to space, no matter what time it is or what the weather may be.
Over the past decade, engineers were searching for such a material, and they finally found it: reflective films made from microscopic layers of mixed polymers and oxides. Carefully manipulated through nanotechnology, these films maximize only the radiation of wavelengths between eight to thirteen micrometers, the exact wavelength of the unwanted heat. Much like solar panels, these films can be installed on roofs and connected to current refrigeration systems to effectively banish the warmth to space without requiring any outside energy whatsoever, even during the day.
Only recently developed, this space-powered cooling technology is expensive to produce. However, as one such company, SkyCool, boasts, their radiative cooling panels reduce electricity costs by fifteen to forty percent. So, why stop with refrigerators? Scientists hope to use radiative cooling to replace air conditioning, providing a much-needed alternative as air conditioners make up ten percent of all global electricity consumption (International Energy Agency). Companies are already connecting radiative cooling panels to existing cooling systems in grocery stores, universities, hospitals, and offices. As production costs decrease, its reach will only spread.
It could still be a while until space powers freezers for snowmen. But it’s possible—and engineers are developing technology right now to make it a reality.
“The Future of Cooling.” IEA, May 2018, https://www.iea.org/reports/the-future-of-cooling. Accessed 18 January 2021.
Kaplan, Sarah. “Bringing the Chill of the Cosmos to a Warming Planet.” The Washington Post, 7 October 2020, https://www.washingtonpost.com/climate-solutions/2020/10/07/radiative-cooling-climate-change/?arc404=true. Accessed 18 January 2021.
“SkyCool Systems – Bringing electricity-free cooling to the world.” YouTube, uploaded by SkyCool Systems, 10 December 2020, https://www.youtube.com/watch?v=CMaZfuInd9c. Accessed 18 January 2021.
Smith, G., Gentle, A. “Radiative cooling: Energy savings from the sky.” Nat Energy 2, 17142, 4 September 2017. https://doi.org/10.1038/nenergy.2017.142
Sun, Xingshu, Sun, Yubo, Zhou, Zhiguang, Alam, Muhammad Ashraful, and Bermel, Peter. Radiative sky cooling: fundamental physics, materials, structures, and applications. de Gruyter, 29 July 2017, https://www.osti.gov/biblio/1424949. Accessed 18 January 2021.
Photo credit: https://web.colby.edu/humanslashnature/files/2015/09/fridge-in-space.jpg