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Baseline model with a wedge cut out to show the interior. Credit: U. S. Department of Energy Ames National Laboratory
Scientists have developed a magnetocaloric heat pump that matches conventional systems in cost, weight, and performance, eliminating harmful refrigerants. By optimizing materials and design, the pump achieves comparable power density, offering a greener and efficient alternative for heating and cooling.
Researchers from the U.S. Department of Energy’s Ames National Laboratory have developed a magnetocaloric heat pump that rivals traditional vapor-compression heat pumps in terms of weight, cost, and performance. Vapor-compression technology, which has been the foundation of heating and cooling systems for over a century, relies on refrigerants that pose significant environmental risks. These refrigerants contribute to global carbon emissions and, when leaked, release chemicals harmful to both humans and ecosystems.
Magnetocaloric heat pumps offer a promising alternative for heating and cooling by eliminating refrigerant emissions and operating with greater energy efficiency. However, until now, magnetocaloric devices have struggled to match vapor-compression systems in all three critical areas: weight, cost, and performance. This new advancement marks a significant step toward more sustainable heating and cooling technology.
Julie Slaughter, the research team leader, explained that their investigation began by building a magnetocaloric heat pump. “We first looked at what is out there, and how close the existing magnetocaloric devices are to matching compressors,” she said. “Next we developed a baseline design and then asked, ‘Okay, now how far can we push the technology?’”
A magnetocaloric heat pump works by changing the magnetic field applied to a magnetocaloric material while pumping fluid to move heat. Slaughter explained that this is typically done with permanent magnets. The core of the device involves spinning permanent magnets relative to the magnetocaloric material and using magnetic steel to keep the magnetic field contained. The arrangement of these three pieces plays a major role in the team’s predictions as they examined how to make the heat pump more power-dense.
Advancing Material Use and Efficiency
Another part of their investigation involved evaluating the two most common magnetocaloric materials used in these heat pumps. Gadolinium and lanthanum-iron-silicon-hydride-based material.
“In our baseline device, we kept it simple by using a single material, gadolinium. Lanthanum-iron-silicon materials have a higher power capability than gadolinium. So, that naturally increases the power density. They’re just not as readily available and require multiple materials in one device to get good performance,” said Slaughter. “In our evaluations, we included estimates of LaFeSi performance for the most power-dense devices.”
Slaughter’s team focused on using space and materials more efficiently, and reducing the amount of permanent magnet material and magnetic steel needed for the pump to operate efficiently. These efforts helped to make the core system pieces match the weight of compressors available today.
“We were able to show that we are competitive with the power density of some of the compressors that are out there today,” said Slaughter. “The permanent magnets and the magnetic steel make up most of the mass rather than the expensive magnetocaloric material, and that’s really helpful for affordability. We assumed, if a device weighs about the same, the cost will be about the same in mass production.”
Reference: “Scalable and compact magnetocaloric heat pump technology” by Julie Slaughter, Lucas Griffith, Agata Czernuszewicz and Vitalij Pecharsky, 28 October 2024, Applied Energy.
DOI: 10.1016/j.apenergy.2024.124696
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