‘Potential for … large-scale application’

Photo Credit: Hong Kong University of Science and Technology

A team led by researchers at the Hong Kong University of Science and Technology may have found a more eco-friendly alternative to traditional cooling systems, allowing people to stay cool without heating up the planet.

Air conditioning is great for keeping homes cool but also contributes to warming the climate, as some of the electricity consumed to power AC units comes from dirty energy. As detailed in a university report posted by Tech Xplore and a corresponding study published in Nature, the team of researchers developed the world’s first-ever “kilowatt-scale elastocaloric green cooling device.”

Elastocaloric cooling, a form of solid-state cooling, uses shape memory alloys (SMAs) to cool homes without emitting heat-trapping gases, according to the university’s report. It’s also highly energy-efficient, making it a promising alternative to commercial ACs. However, previous elastocaloric cooling devices couldn’t pass the kilowatt-scale threshold needed for commercial ACs.

The researchers discovered two core issues that prevented previous devices from meeting the kilowatt-scale requirement. First, the devices struggled to balance the refrigerant’s specific cooling power with the total active mass. Second, the devices couldn’t transfer heat efficiently enough for high-frequency operation.

To address these issues, the team proposed a multi-cell architecture design they referred to in their study as “SMAs in series — fluid in parallel.” Per the report, this design links 10 elastocaloric cooling units along the force application direction, with nickel-titanium alloy tubes contained in each unit.

The tubes boost the device’s heat exchange efficiency. The parallel fluid channels also help improve efficiency by keeping the system pressure under 1.5 bar, ensuring its stability during high-frequency use.

The proposed design replaced traditional distilled water with graphene nanofluid, a heat transfer medium that can conduct heat 50% more effectively, even at just two grams per liter concentration.

As the Tech Xplore post explained, researchers tested the cooling device in a 2.7-cubic meter model house in a summer outdoor environment and managed to stabilize indoor temperatures at 21-22 degrees Celsius (about 70-72 degrees Fahrenheit) within 15 minutes, even when outdoor temperatures were at 30-31 degrees Celsius (about 86-88 degrees Fahrenheit). This reportedly marked the first time an elastocaloric cooling device has surpassed the kilowatt-scale threshold.

“This achievement demonstrates the potential for the large-scale application of elastocaloric cooling technology,” said Professor Sun Qingping, one of the lead researchers, per the publication. “We are working with the industry to drive its commercialization.”

With global temperatures rising, the demand for air conditioning and cooling also grows. Per Our World in Data, the International Energy Agency has estimated that the demand for air conditioners could triple by 2050.

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Air conditioning accounted for approximately 3% of global heat-trapping carbon pollution and 7% of global electricity consumption as of 2022, according to the same report. These percentages are likely to rise with the growing demand for AC and cooling.

If the research team’s breakthrough allows elastocaloric cooling technology to become commercially available, consumers could be able to lower their electricity bills and reduce their reliance on dirty energy. Pairing it with green energy solutions like installing solar panels could further improve energy efficiency while helping homeowners reduce carbon footprints.

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