Elastocaloric Technology To Heat Pumps: Hold My Beer

July 22, 2024July 22, 20247 months ago Tina Casey 0 Comments

Sign up for daily news updates from CleanTechnica on email. Or follow us on Google News!

Last Updated on: 22nd July 2024, 11:43 am

The heat pump revolution is providing buildings, factories, and other facilities with the power to ditch fossil energy from climate control systems. That’s just for starters. Another wave of energy efficient, planet-saving technology is also emerging in the form of new elastocaloric heating and cooling systems, and the US Department of Defense is there for it.

The Heat Pump Revolution Is Here To Stay

To be clear, heat pumps aren’t going away any time soon. They are widely acknowledged to be significant drivers of decarbonization, as an economical means of replacing oil and gas HVAC systems with electricity. Heat pumps are also far more energy efficient than baseboard electric heating systems.

In past years, residential heat pumps were mainly popular in warmer parts of the US. Following a recent series of technology improvements, they are also making inroads all over the country, including regions that experience severe winters. A healthy assist from the 2022 Inflation Reduction Act is also spurring interest. As a result, heat pumps are now outselling conventional furnaces in the US.

Heat pumps are also getting bigger and more powerful, to handle industrial-scale chores. Volkswagen’s new Scout Motors electric vehicle factory in South Carolina, for example, has commissioned a massive pair of heat pumps for its HVAC system.

Heat Pumps, Meet Elastocaloric Technology

In contrast, elastocaloric technology has some catching up to do. The R&D phase been building momentum over the past 10 years or so, but the most recent milestone is a couple of projects that demonstrate a cooling system the size of a mini-fridge.

Still, the progress has been substantial enough to attract notice from the PV Magazine. Last week, the publication reviewed ongoing R&D work at the University of Saarland in Germany under the headline, “Elastocalorics could replace heat pumps, air conditioning systems.”

“Elastocalorics have the potential to replace current air conditioning and heating systems, offering significant energy savings when paired with technologies such as photovoltaics,” the subheading emphasized.

Closer to home, researchers at the University of Maryland’s James A Clark School of Engineering have also been working on an elastocaloric system. “Caloric materials, including magnetocaloric, electrocaloric, and elastocaloric materials can undergo phase transition and release and absorb heat upon application of various fields,” the school explained in an article last year.

“The key feature of the elastocaloric system is the compression and release of fatigue-resistant nitinol (NiTi) tubes configured in a versatile, multimode heat exchange architecture,” they added.

Nitinol has crossed the CleanTechnica radar here and there in recent years. The NASA-developed, shape-memorizing alloy of nickel and titanium has been put to use in airless bicycle tires as well as medical implants and aerospace applications.

In terms of the potential to replace heat pumps and other HVAC systems, nitinol generates a cooling effect simply by being stretched. It can also be tweaked to generate heat.

On Beyond Heat Pumps

That sounds simple enought, but the devil is in the details. The Clark School cites research team co-leader Professor Ichiro Takeuchi, who indicates that the road to a working NiTi system was a long one. “More than a decade ago, we were just playing with a NiTi wire,” Professor Tekeuchi explained. “By stretching it, you could get a substantial cooling effect one could feel by hand.”

“That was when we started thinking about applying the concept to a cooling device,” he continued.

If that thing about stretching indicates that the material will eventually break, the Clark team is already on the case. The school has been getting a healthy assist from the US Department of Energy, which lent its Ames National Laboratory in Iowa to aid in the development of a 3D-printing process to fabricate a highly durable nitinol structure.

The 3D process was described in a 2019 study in the journal Science under the title, “Fatigue-resistant high-performance elastocaloric materials made by additive manufacturing.”

Elastocaloric Cooling For Military Vehicles

Last year, the Clark team developed a prototype with a capacity of 200 watts, which the school describes as “enough to power a compact wine fridge.” With scale-up in sight, the researchers are working towards window AC units and the eventual goal of whole-house and commercial HVAC systems.

In the meantime, researchers at Ames are focusing on an elastocaloric project with the goal of developing a new AC system for military vehicles. The Department of Defense needs a new AC system because older refrigerants are being phased out due to their impact on global warming. A new, less harmful refrigerant called HFO-1234yf is on the market, but the DOD has determined that it is not suitable for use in military vehicles due to fire hazards.

The new AC system will leverage nitinol with some special military tweak engineered by the Ames team, spearheaded by researcher Julie Slaughter.

“Normally, if you take a metal and you stretch it, the force gets bigger as you stretch it more. For superelastic materials, you stretch it a little bit, and then, all of a sudden, it just moves with very little added force,” Slaughter explained in a press release dated March 14.

“The material is going through a phase transition when it does that and when that phase transition happens, you also release heat, which causes a temperature change,” she added.

The problem is that the larger the temperature change, the more stress and potential for breakage. A change of around 5°C is manageable, but the Ames project has set a target of around 25°C for the new system to operate as effectively as a conventional cooling unit.

To get there, Slaughter’s team is working with industry partners ATI Specialty Alloys and Components and the German firm G.RAU Inc. to develop a system that deploys a corps of water-based regenerators.

“I see this project as a good first step,” Slaughter explains, indicating that the day of a nitinol-cooled military vehicle is somewhere off in the future.

Meanwhile, we’ll always have heat pumps. In addition to heat pump applications in HVAC systems, heat pumps are also turning up in electric clothes dryers and water heaters, and they are becoming essential equipment for electric vehicles, too.

Follow me via LinkTree, or @tinamcasey on Threads, LinkedIn, and Instagram.

Image (cropped): Researchers are developing high-efficiency elastocaloric technology to replace heat pumps and other HVAC systems, eventually. Credit: Jiaqi Dai, courtesy of University of Maryland Clark School of Engineering.