rethink sustainability
How do we stop cooling systems heating the planet?
Although artificial refrigeration has been in widespread use for scarcely a century, refrigeration itself is an ancient practice. As early as 1780 BC, the Mesopotamians harvested ice from shallow pools that they filled with water on clear winter nights for storage in specially designed ice houses1. There, it would stay frozen for use throughout summer in food storage, cold drinks and perhaps the occasional sorbet. That this was possible is fairly astonishing since, in these desert climates, subzero temperatures are meteorological unicorns.
Happily, we’ve since replaced such techniques with artificial cooling systems that offer cold on tap. Happily, that is, but for the fact that these systems aren’t sustainable. In search of a solution, some scientists and entrepreneurs are turning to the phenomenon that allowed the Mesopotamians to conjure ice in the desert almost 4000 years ago.
Cause and effect… and cause
Artificial cooling systems have had a profoundly positive impact on society, and not just in democratising fresh food storage. They also enable us to stay cool year-round; which is vital not just for comfort, but also cognitive performance. Cooling systems are, therefore, vital economic drivers in warmer climates, many of which host developing nations.
So, we have every reason to want more artificial cooling. Except one. In a cosmic irony, cooling systems are a significant contributor to global warming. They account for 17% of global energy consumption and use refrigerants that release greenhouse gasses thousands of times more potent than carbon dioxide2. Worse, cooling systems will proliferate more quickly as the planet warms, and the concurrent drop-off in emissions from heating systems won’t be enough to compensate3.
In short: the demand for cooling systems is driving climate change, and climate change is driving demand for cooling systems. While a favourable tailwind from renewable and nuclear energy would ease this dangerous feedback loop, an issue as existential as climate change demands a broader range of proverbial egg baskets.
The ancient Mesopotamian ice trick
So, how did the Mesopotamians make ice in the desert?
If left to its own devices, a relatively warm puddle of water will usually lose heat until its temperature is equal to that of its environment. One way it does this is via a process known as radiative cooling: water cools when it radiates more infrared light than it absorbs from its surroundings. Crucially, though, air can’t absorb infrared with wavelengths within a specific range4. So, on nights without clouds that would otherwise radiate heat back down to Earth, any infrared light the puddle emits within this range—known as the transmission window—will escape through the atmosphere into space. The counterintuitive result: the puddle actually gets colder than the surrounding air, freezing if its temperature drops below 0ºC.
In today’s world of artificial cooling systems, this quirk of physics that was once so useful for making ice in the desert might seem like nothing more than a cool piece of trivia. But what if we could somehow use this trick to make these systems more efficient?
One startup, SkyCool Systems, aims to do just that, using a new, high-tech material with two key features. First, it’s too reflective to be heated up by the sun. Second, its nanostructure is designed to radiate as much infrared light as possible through the atmosphere’s transmission window. As a result, this material does something even weirder than water on a clear night: it gets cold when placed outside under the sky, even when placed in direct sunlight. Using this material, SkyCool has built panels that can cool water without electricity, and without evaporating water, which, when integrated into an air conditioning system, will make them 15% to 30% more efficient depending on how many panels are used5.
The technology is mature and ready for market deployments. With further investment and development, research suggests that we could eventually create a material that stays an astonishing 42ºC colder than the surrounding air, even under direct sunlight. Such a material could allow us to make cooling systems up to two-thirds more efficient, or even to create new cooling systems that need no electricity at all.
A cool future?
The need for such solutions is only going to become more urgent, and not just for keeping people cool.
As of 2016, data centres were responsible for 3% of the world’s energy consumption—more than the entire UK—and 2% of the world’s greenhouse gas emissions—about the same as the aviation industry. Server cooling is responsible for a significant proportion of data centres’ overall energy consumption—and that consumption is doubling about every four years6.
Radiative cooling could also be harnessed to improve the output of renewables. Solar panels, for instance, would generate more electricity if they could be made to stay cool under the sun’s rays.
And if we could leverage the vast temperature difference between Earth’s surface and outer space to power a heat engine, radiative cooling could itself become a source of renewable energy.
Of course, such innovations are a way off. But, for investors, this potential represents a tantalising opportunity both for significant returns and to propel a paradigm shift in sustainability. With their capital, investors have the means to power R&D. And, as new radiative cooling technologies become available, investors can incentivise businesses that manufacture or use cooling systems to incorporate these innovations for energy efficiency.
Renewable and nuclear energy will play an essential role in solving climate change. But the challenge is too urgent, and the consequences of failure too grave, not to explore more options. Radiative cooling is an exemplar of how science and innovation can reveal whole new avenues toward a more sustainable future, with extraordinary investment opportunities besides.
1 James, P. and Thorpe, N. (1994) Ancient Inventions, United States, Ballantine Books.
2 Coulomb et al. (2015) ‘The Role of Refrigeration in the Global Economy’. Available here.
3 Henley, J. (2015) ‘World set to use more energy for cooling than heating’. Available here.
4 Specifically, infrared light with wavelengths between eight and 13 microns.
5 Raman, A. (2018) ‘How we can turn the cold of outer space into a renewable resource’. Available here.
6 Bawden, T. (2016) ‘Global warming: Data centres to consume three times as much energy in next decade, experts warn’. Available here.
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