Developed at the U. S. Ames National Laboratory, the novel magnetocaloric heat pump utilizes gadolinium as the working medium and reportedly matches current vapor-compression heat pumps for weight, cost, and performance. The system is based on a packed-particle bed active magnetic regenerator, a magnetic source composed of permanent magnets and high permeability magnetic steel.
Scientists at the US Department of Energy’s Ames National Laboratory have built a prototype of a magnetocaloric heat pump (MCHP) that purportedly matches current vapor-compression heat pumps for weight, cost, and performance.
MCHPs use the magnetocaloric effect to perform heating and cooling. This effect consists of the cooling or heating of magnetic materials with the variation of an externally applied magnetic field. It is commonly utilized to develop highly energy-efficient cooling or heating systems that require no harmful refrigerants.
In MCHPs, the temperature changes through a variation of the magnetic field, with these caloric effects being employed to transfer thermal energy and produce heating or cooling power. All of these systems are relying on an active magnetic regenerator (AMR) concept, where a heat transfer fluid is actively pumped through a bed of magnetocaloric material in order to transfer thermal energy to hot and cold side heat exchangers.
“Magnetocaloric heat pumps are a promising replacement for cooling and heating,” the research’s lead author, Julie Slaughter, said. “They can eliminate refrigerant emissions and require less energy to operate.”
In the study “Scalable and compact magnetocaloric heat pump technology,” which was recently published in Applied Energy, the research team explained that the system is based on a gadolinium packed-particle bed active magnetic regenerator (AMR), as well as on a magnetic source composed of permanent magnets and high permeability magnetic steel.
“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, noting that the evaluations included estimates of a base magnetic refrigerating material known as LaFeSi.
These evaluations were intended to find ways to increase the power density of the proposed heat pump system, with the scientists seeking to optimize magnetic field sources and AMR geometries while reducing space and materials. The estimations were made for cooling powers ranging from 37 W to 43.5 kW.
“These efforts helped to make the core system pieces match the weight of compressors available today,” Slaughter said, adding that the gadolinium material used was specifically designed to exhibit high system power density (SPD). “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.”
The analysis showed that the system’s SPD increased from a baseline of 5.9 W/kg to 81.3 W/kg. “We project that magnetocaloric heat pump SPDs are competitive with vapor compression up to 1 kW of cooling power,” the academics said. ” In the limiting case, the maximum expected power density of MCHPs of a similar design is 114 W/kg, which matches compressors up to approximately 3 kW of cooling power.”
“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
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