As the planet warms, researchers and startups are developing innovative technologies for a cooler and more energy-efficient future
As our planet heats up, so too does demand for cooling technology. Energy use for space cooling will more than triple by 2050 according to a 2018 report by the International Energy Agency. But air conditioning units are power hogs — accounting for about 10% of worldwide electricity consumption — and contain a hydrofluorocarbon refrigerant that is a more potent greenhouse gas than carbon dioxide.
“It’s a vicious cycle,” says environmental engineer Shelie Miller, director of the University of Michigan’s Program in the Environment. “It becomes warmer, so we turn up our air conditioners, which consume more energy. When we use more energy, more greenhouse gases are released, causing it to get even warmer.”
How do we deal with this conflict? It’s a problem that scientists and engineers are working to solve by developing more sophisticated, energy-efficient cooling technologies.
The concept of air conditioning dates back centuries.
“Enhancements in HVAC (heating, ventilation, and air conditioning) technology are continually improving the efficiency of cooling services, and switching to renewable energy sources that reduce greenhouse gas emissions can reduce the overall impact,” Miller says. “Throughout history, people have come up with innovative ways to cool buildings without the use of energy-intensive air conditioning.”
The concept of air conditioning dates back centuries. Ancient Persian engineers built “badgirs,” which are wind catchers that funnel cool breezes down to houses, and “yakhchāls,” conical structures used to make ice that were one of the first refrigerators in the desert.
In 1820, inventor Michael Faraday discovered that compressing and liquefying ammonia and then allowing it to evaporate could cool the air. In 1902, engineer Willis Carrier designed an apparatus for the Sackett & Wilhelms Lithographing and Printing Company in New York that circulated air over coils chilled by compressed ammonia to control humidity when printing in color. Carrier eventually turned his design into the world’s first electrical air conditioner, which debuted in 1925 in Times Square’s Rivoli Theater, heralding the days of watching summer blockbuster films in air-conditioned theaters.
Air conditioners were considered a luxury when first introduced for consumers, but their ability to remove humidity from the air and reduce air temperature during warm conditions rapidly made them a necessity in hot climates. The vast postwar migration to America’s Sun Belt states would have been impossible without the spread of air conditioning, as would the growth of tropical cities like Hong Kong and Singapore. (Lee Kuan Yew, Singapore’s founding father, dubbed air conditioning the most important invention of the 20th century.)
Cooler air is vital for keeping produce fresh, preserving medicine and vaccines, and cooling down data centers that power the internet. Keeping cool has been shown to be important for health, well-being, and increased productivity. Today, researchers and startups are harnessing more energy-efficient sources to generate the coolness we crave — from shape-shifting metal alloys to renewable energy and the cold of the sky.
A research team at Saarland University in Germany is eliminating the need for refrigerants by developing shape-memory alloys. Deforming or pulling a nickel-titanium wire or sheet creates stress for the alloy and raises its temperature. When the material is brought back to its original shape, it cools down to around 20 degrees below ambient temperature.
“The basic idea was to remove heat from a space — like the interior of a refrigerator — by allowing a pre-stressed, super-elastic shape memory material to relax and thus cool significantly,” explained Stefan Seelecke, professor for intelligent material systems at Saarland University, when the project was announced.
The team has created a prototype, a patent-pending cam drive that is a rotating bundle of shape-memory wires used to amplify cooling power. The device could operate as a heat pump, an air conditioner, or even a refrigerator, all without any environmentally harmful refrigerants. The German Research Foundation has been funding the project since 2016, with the European Commission and the U.S. Department of Energy considering it a promising alternative technology to existing vapor-compression refrigeration systems.
For clean-tech startup Blue Frontier, renewable energy is key to a more efficient cooling system. The company started in Florida in 2013 as Be Power Tech, which developed an air conditioner that produced its own electricity using a natural gas fuel cell. But CEO Daniel Betts found that the market for the technology was limited to buildings powered by natural gas, and fuel cells were too expensive for early market adoption.
Betts then partnered with engineers from the National Renewable Energy Laboratory to redesign the system. The result was an air conditioner with thermochemical lithium chloride energy storage, which stores a high-concentration salt solution and converts it to chemical energy for later use. “Solar power generation grows throughout the morning and wanes starting in the early afternoon,” says Betts. “The electric load in buildings tends to peak in the early to late afternoon, leading to a mismatch between generation and consumption.” Blue Frontier’s air conditioner is equipped with the ability to store cooling energy, so it only uses electricity during maximum solar power production. “With our technology,” Betts says, “we can consume electricity only when there’s no grid congestion and when renewable energy is a bigger part of the electricity mix.”
Meanwhile, California-based SkyCool Systems turned to the night sky for its cooling technology. Founded in 2016, the startup originated at Stanford University and has since raised $990,000 in funding from grants provided by the university’s StartX Fund and the U.S. Department of Energy’s Advanced Research Projects Agency.
To understand how SkyCool Systems’ cooling technology works, consider any material facing the sky at night. “If it’s looking up at the sky, it would naturally send out its heat as something called thermal radiation,” says scientist and co-founder Aaswath Raman. “When this thermal radiation is sent to the sky, some fraction of it escapes into space. Because of that, any surface facing the sky at night will naturally cool down to below the air temperature.”
Mimicking this natural phenomenon during the day proves more difficult. “The sun will naturally heat up any material — enough to counteract this cooling effect,” says Raman. “We need a material that reflects sunlight really well but continues to send out heat. When you have those two things together, you could enable this effect during the day as well. That becomes compelling because then you have access to free passive cooling in the middle of the day, which is when we need cooling the most.”
“The target energy savings and demand reduction might be anywhere between 10% and 30%.”
SkyCool Systems developed silver panels that look like solar panels but are instead covered in an optical film that converts heat into a mid-infrared wavelength range to slip through the atmosphere and get cast into space while also reflecting sunlight away. The company’s panels are currently deployed at five sites, including an office building and a convenience store, and are integrated with existing cooling systems, such as coolers, freezers, ice machines, and air conditioning systems.
Engineer and co-founder Eli Goldstein says the benefits of SkyCool Systems’ cooling panels are threefold. “One is energy savings, another is demand reduction, and the third is increasing the cooling capacity of a system,” he says. “The target energy savings and demand reduction might be anywhere between 10% and 30%.”
Moreover, the cooling mechanism requires no energy or water. “It’s effectively passive in its form of cooling, so it doesn’t use any energy and water,” says Goldstein. “There’s no evaporative water loss to generate this cooling, so it’s a much more sustainable approach.”
These cooling technologies are not without their challenges. SkyCool Systems is trying to scale up as quickly as possible to keep up with market demand, and though Blue Frontier’s technology has been proven through various prototypes, the company still needs to establish mass production and field trials.
They might not have reached wide-scale adoption yet, but these innovations are paving the way for a cooler and more energy-efficient future. Blue Frontier plans to move toward an “air conditioner as a service” model while SkyCool Systems envisions replacing air conditioning systems with its panels.
“Cooling is important to our everyday lives,” Goldstein says. “We need to work together to get more efficient systems and run them in a sustainable way.”
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