The more the planet warms, the more we’ll need to cool down. Yet, our cooling systems are…heating…the Earth as they consume fossil-fueled energy and release greenhouse gases.1 Air Conditioning use is expected to increase from about 3.6 billion units to 15 billion by 2050.2 So, how do we exit this…cold room…trap? What if I told you we could tap into space for electricity free air conditioning and other refrigeration tech?

Putting a freeze on low-efficiency cooling

One of the…chilling…effects of climate change is heatwaves. Last June, a record-breaking temperature of 121.3F (about 50C) triggered 130 deaths in Vancouver.3 And this is going to get worse. You may argue that setting your AC to full blast would fix the problem, right? While it would definitely avoid you melting down in the short term, it will have the opposite effect on a global scale in the long run. Air conditioning and refrigerators use hydrofluorocarbons (HFCs) as coolants. While they have a much shorter lifespan in the atmosphere compared to CO2, HFCs are thousands of times more potent than carbon dioxide as a greenhouse gas. These…uncool…gases leaking from cooling equipment contribute about 4% of global GHG … twice as much as aviation.4 The other issue is that a typical AC unit is a dirty, energy-hungry machine. According to the International Energy Agency’s Future of Cooling report5, if we don’t find more energy-efficient alternatives, by 2050 indoor cooling systems will consume as much electricity as do China and India today. You may see why you’re walking on thin ice on the way to buy a new AC. But it’s not just about the AC in our houses. We need refrigeration in supermarkets to store food safely. Not to mention the facilities to cool down the massive data centers that support and connect our digital world. All these combined currently account for 8% of greenhouse gases released in the atmosphere.6 On the other hand, if we improved the efficiency of cooling, we would cut emissions in half. But how can we do that? A US startup has a cool idea for that: radiative cooling. In short, SkyCool claims they could plug into the biggest freezer in the universe … space … to make our cooling systems more efficient.7 Last February, the California-based company was awarded a $3.5M fund to turn this concept into a reality.8 Let’s take a deep dive into their cool and refreshing space pool.

A cold call to the sky

Everything on Earth, including all of us, emits heat as infrared light based on a phenomenon called thermal radiation. Any sky-facing surface will release this energy in the atmosphere, which absorbs some of it. But there’s a … cool hole … between the 8 and 13 µm (micrometers) wavelengths, where the emitted heat goes past the atmospheric barrier and actually reaches outer space. As a result of the thermal exchange with the cosmos, which can be as cold as -454F (or -270C), the emitting body gets cooler. This is the radiative cooling process, a heat-shedding effect which peaks on cloudless nights. That’s why it’s also known as night-sky cooling, and why you see frost on the windshield of your car in the early morning even when the air temperature is above freezing. And it’s not a new invention. Hundreds of years ago ancient Persians used it to make ice and preserve food in the desert well before artificial refrigeration was introduced.9 They built sky-facing shallow pools and filled them with water. On a clear night in the desert, their ice houses worked like magic. Except it wasn’t magic but radiative cooling that made the water surface drop below the air temperature and reach 32F (or 0C).10

That sounds…cool…right? So all we need to do is channel the infrared thermal radiation into this gateway to space and the heat won’t be trapped in the atmosphere, which means it won’t add to the greenhouse effect. The only problem is, during the day when we would need cooling systems the most, sunshine obscures the space freezing effect. So, what do we do?

Leveraging a combination of nanotechnology and photonics, SkyCool designed a material by alternating 7 layers of a highly reflective component like hafnium oxide and a weakly reflective compound such as silicon dioxide.11 They optimized the thickness of each layer based on ideal solar reflectivity and emissivity over the 8–13 µm wavelength range. As a result of this special setup, their film sends infrared rays out through the sky transmission window and reflects 97% of sunlight.12 That’s pretty impressive if you compare it to commercially available white paint, that reflects only 80 to 90% of sun rays.13 I guess someone may argue this is not a huge difference and that standard white paint could also do the job. However, if you consider a 100 sq meter roof (about 1,000 square feet), an extra 1% of reflectance would give you an additional cooling power of about 1 kW. So when comparing it to commercially available white paint, that could be about 10 kW of additional cooling power for that 100 sq meter roof. That’s more cooling power than a standard central air conditioner we use in our houses.14

40 times thinner than a human hair, SkyCool applies this film on top of their fluid cooling panels that can function at any time of the day and not just at night. The aluminum modules cool a water-glycol fluid flowing within some pipes and their temperature can drop by up to 15F (or 10C) below ambient temperatures even when constantly exposed to blazing sunlight. Using the chilled fluid, SkyCool’s panels lower the temperature of the cooling systems’ refrigerants, which increases their efficiency. By how much? About 12% based on the field trial the startup performed in California back in 2014. But on their website they claim the efficiency could reach up to 40%.

This cooling tech could replace AC systems in some cases, reducing energy consumption by up to 90%. According to the company, their panels save up to 3x more energy than a standard solar panel generates in electricity using the same space. The icing on their panel cake is that they don’t need water evaporation to cool and can be recycled at the end of their life. All this sounds amazing, right? So, what about practical applications?

SkyCool is currently running a few commercial pilots to solve real-world problems. For instance, they installed 15 rooftop cooling panels and connected them to the walk-in freezer of a convenience store in Sacramento, California.15 The freezers’ daily energy consumption went down by 15%. The company also replaced the condensers of the ice machines inside the store with 15 more panels, achieving a 25% reduction in its energy use.

SkyCool also came to the rescue of a Grocery Outlet supermarket in Stockton, California. The store was spending $40,000 per year to run its electricity-hungry refrigeration system and keep their food safe. By installing an array of 32 panels on the store’s roof, SkyCool estimated a 36 MWh energy reduction per year, which translates into nearly $6,000 of annual savings.

Another hot topic SkyCool is quenching is energy-demanding data centers. With 80% of these powered by fossil fuels, data centers alone account for ca. 0.3% of the global carbon footprint.16 17 Their emissions are partly caused by inefficient cooling systems, which is based on the traditional vapor compression. Using their panels to reject heat from the server racks, Skycool attained an energy saving of 1,036 kWh/m2/year without relying on any compressors or fans. While the startup pilots are promising, are there any other companies in this space? And what about the technology’s economic viability?

The air conditioner of the future?

Since SkyCool’s film discovery, researchers have developed other materials harnessing the radiative cooling principle. For instance, a recent study from the University of Buffalo suggested that the passive cooling strategy could be used as an electricity-free system on its own.18 Scientists designed a polymer-aluminium hybrid film, whose structure can tune the direction of the emitted infrared rays skywards and radiate heat from buildings. This innovation makes the technology less dependent on environmental conditions and more effective in urban areas with many obstacles such as skyscrapers. But it’s not just about films.

PARC engineered a self-cooling paint that cools any surface up to 10C/18F below the surrounding air.19 The Silicon Valley-based company already tested their spray-on solution on a number of substrates, ranging from steel to carbon fibers. With a daytime cooling power of around 100 W/m2 in summer, PARC tailored their paints to the building and automotive industries.

Engineers from Purdue University created an ultrawhite paint that reflects 98.1% of sunlight. They achieved this whopping mirror effect by using barium sulfate particles of different sizes, which reflects multiple wavelengths.20 Given the low-cost raw material, scientists said their paint could be competitive on the market within a couple of years.

But are these ultra-pale paints more cost-effective than conventional ones? Australian researchers painted a picture about that. Based on their review, scientists concluded you would be better off using standard paints in moderate climate zones. This is because the benefit of using whiter heat-reflective paints is too small to justify their added costs.21 Yet, another study confirms cool paint can be an efficient and profitable solution in tropical climates like Singapore.22 Scientists estimated coating cement roofs with cool paint would reduce energy expenses by up to $57/m2 per year and its implementation costs would be paid back in as early as 2 years.

Besides inorganic materials, it turns out we can use organic ones as well. A refreshing collaboration between the University of Colorado and the University of Maryland gave birth to a sort of … woody ice cube.23 By removing lingnin, the component giving the brown color and strength to wood, the researches were left with a pale wood made of cellulose nanofibers. They then compressed the treated material to increase their strength and added a super hydrophobic coating to keep water away. The bright white wood brick can be used to build heat-repellent roofs. When testing it on a farm in Arizona, the processed wood stayed 12 degrees cooler than the natural material. Researchers estimated that US buildings constructed after 2004 would save on average 20% of cooling costs by using their wood. Their efforts led to the creation of the InventWood startup which is working on commercializing the product.24

In addition to saving electricity bills, radiative cooling could be a geoengineering strategy to freeze Earth’s global warming.25 However, this would mean coating up to 2% of the planet’s surface with super cool materials, which is pushing it a bit. While being the most ready-to-cool technology, SkyCool’s energy savings have been based on a limited amount of data so far. To add to that, local climate conditions can negatively impact the panels’ performance. Clouds and especially low fog could reduce their efficiency by up to ca. 30%. Same applies to water vapor that captures some of the infrared radiation before it could reach space. Also, even though the company touts being able to provide renewable electricity-free cooling, they still need electricity to power the pump for recirculating the fluid within their panels. As said by their founders, while SkyCool’s scientific innovation is promising, they will have to tinker with the technology to make it cheaper before it could be commercialized.26 The main challenge is to drive down the module’s manufacturing and installation costs. Based on a Pacific Northwest National Laboratory study, if the cost of making and setting up SkyCool-like materials was to be kept below $6.25 per square meter of rooftop, it’ll be paid off by the energy savings in five years.27 Thanks to the partnership with 3M and the recent $3.5 million grant they received, SkyCool believes their films can hit a market-friendly price by 2023, with a payback time as short as 3 years.28

Space for future improvement

With the planet becoming hotter and hotter, the introduction of more efficient and eco-friendly cooling tech can’t be kept on ice. SkyCool has dug out a galactic sink to dump heat into … and more are diving into it. While the mass production of space powered cooling materials isn’t viable today, technology advancements could make this a reality soon.

  1. “The air conditioning trap: how cold air is heating the world | Energy ….” 29 Aug. 2019 ↩︎
  2. UN Environment Program – “Climate-friendly cooling could cut years of Greenhouse Gas Emissions and save US$ trillions: UN” ↩︎
  3. “Canada weather: Dozens dead as heatwave shatters records – BBC ….” 30 Jun. 2021 ↩︎
  4. “How cleaning up coolants can cool the climate – why HFCs are ….” 4 May. 2021 ↩︎
  5. “The Future of Cooling – Analysis – IEA.” ↩︎
  6. “Aaswath Raman: How we can turn the cold of outer space into … – TED.” 1 Jun. 2018 ↩︎
  7. “SkyCool Systems: Home.” ↩︎
  8. “$3.5m funding for radiative cooling technology – Cooling Post.” 9 Feb. 2021 ↩︎
  9. “Radiative cooling – Wikipedia.” ↩︎
  10. “The Persian ice house, or how to make ice in the desert – Field Study ….” 4 Apr. 2016 ↩︎
  11. “Passive radiative cooling below ambient air temperature … – Nature.” 26 Nov. 2014 ↩︎
  12. “Passive radiative cooling below ambient air temperature … – Nature.” 26 Nov. 2014 ↩︎
  13. “‘Whitest ever’ paint reflects 98% of sunlight – BBC News.” 16 Apr. 2021 ↩︎
  14. “‘Whitest ever’ paint reflects 98% of sunlight – BBC News.” 16 Apr. 2021 ↩︎
  15. “Convenience Store Case Study – SkyCool Systems.” ↩︎
  16. “‘Tsunami of data’ could consume one fifth of global electricity by 2025.” 11 Dec. 2017 ↩︎
  17. “How to stop data centres from gobbling up the world’s … – Nature.” 13 Sept. 2018 ↩︎
  18. “A polydimethylsiloxane-coated metal structure for all-day … – Nature.” 5 Aug. 2019 ↩︎
  19. “Self-Cooling Paint – Passive Radiative Cooling Technology | PARC.” ↩︎
  20. “Super-white paint could cut air conditioning bills … – Popular Science.” 22 Apr. 2021 ↩︎
  21. “(PDF) A Review of Heat-reflective Paints – ResearchGate.” ↩︎
  22. “(PDF) Life Cycle Analysis of Cool Roof in Tropical … – ResearchGate.” ↩︎
  23. “CU Boulder and University of Maryland create cooling wood, an eco ….” 23 May. 2019 ↩︎
  24. “Transparent Wood – InventWood.” ↩︎
  25. “The super-cool materials that send heat to space – Nature.” 31 Dec. 2019 ↩︎
  26. “How Aaswath Raman and SkyCool are modifying an ancient ….” 7 Oct. 2020 ↩︎
  27. “Energy Savings Potential of Radiative Cooling Technologies – PNNL.” ↩︎
  28. “This California company wants to make modern AC obsolete.” 27 Jul. 2021 ↩︎

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