Solid state caloric material could make fridges 30% more energy efficient by 2025

Scientists at the research consortium CaloriCool® are closer than ever to the materials needed for a new type of refrigeration technology that is markedly more energy efficient than current gas compression systems.

Currently, residential and commercial cooling consumes about one out of every five kilowatt-hours of electricity generated in the U.S., but a caloric refrigeration system could save as much as 30 percent in energy usage.

Consortium members have filed a pair of provisional patent applications on two caloric materials, which are compounds that generate strong cooling effects when acted upon by magnetic, electric, or mechanical forces. One of the materials has a magnetocaloric effect 50 percent better than any material of this class known before. The second patentable discovery corrects a flaw in an already known material, which was formerly thought to be too brittle to use outside of the laboratory setting.

“Both of these materials are composed of common elements, which means they will be reasonably inexpensive to make in mass production,” said Vitalij Pecharsky, an Ames Laboratory scientist and CaloriCool director. “It’s an important hurdle to overcome for adoption of this technology into appliances and HVAC systems.”

CaloriCool’s ultimate goal is to transfer the solid-state cooling system technology into the marketplace for use in commercially available refrigeration appliances and systems.

At Ames Laboratory a new research consortium called CaloriCoolⓇ launched in 2016 with the idea that refrigeration could be radically better—cheaper, cleaner, more precise and energy-efficient—by abandoning vapor compression for something entirely new: a solid-state caloric system. And this research team plans to do it—including adoption into manufactured systems and products—within a decade.

“It’s like replacing the incandescent light bulb with an LED bulb; the new technology does the same thing, but in a completely different and much more efficient and sustainable way,” said Vitalij Pecharsky, director of CaloriCool. “That’s what CaloriCool will do with the refrigeration and heat pumping industries.”

Established as part of the Energy Materials Network, CaloriCool® is sponsored by the DOE’s Office of Energy Efficiency and Renewable Energy through its Advanced Manufacturing Office, and led by the Ames Laboratory at Iowa State University.

CaloriCool designs, discovers, and deploys materials in which reversible, thermal (caloric) response is triggered by magnetic, stress, and electric fields, or combinations thereof.”

CaloriCool Mission

CaloriCool will design and discover high-performance, caloric energy-conversion materials that can be economically adopted by industry for a new generation of energy efficient solid-state cooling/heat-pumping devices and systems, enabling a broad spectrum of applications ranging from residential and commercial air conditioning, refrigeration and freezing, to gas separation and liquefaction.

CaloriCool Background

Unlike current refrigeration technology that uses vapor compression, requiring significant electrical power and use of various greenhouse gases (GHG), caloric solids can generate cooling when acted upon by magnetic, stress, or electric forces using up to 30% less energy and no GHG. Materials with so-called giant caloric effects have existed for nearly 20 years, but they lack the efficiency and cost-effectiveness needed for successful commercial adoption for home refrigerators, air conditioners, and grocery-store freezers.

Ferroelectric Ceramic (bulk and thick film) Fabrication

Development and synthesis of bulk electrocaloric (EC) ceramics which can reach large electrocaloric response under low electric field.

Penn State University is developing bulk electrocaloric (EC) ceramics which can reach large electrocaloric response under low electric field. For electrocaloric ceramics to be used in cooling test station and devices, EC ceramics should be manufactured in multilayer form similar to multilayer ceramic capacitors (MLCC) to attain high EC response at voltages on the order of 200 V with high reliability. A first step to transition these bulk ceramics into EC multilayer ceramics is to study the synthesis conditions of ceramic thick films.

Penn State has extensive bulk ceramic synthesis capabilities, including powder preparation, ceramic synthesis and composition characterization of ceramic materials. In addition, the university operates unique ceramic thick film fabrication facilities that allow the preparation of ceramic layers down to 10 mm thickness. Collaborations with industrial partners enables the further conversion of thick EC films into EC multilayers using the MLCC fabrication technology.

New Testing System

Researchers at the U.S. Department of Energy’s Ames Laboratory have designed and built an advanced model system that successfully uses very small quantities of magnetocaloric materials to achieve refrigeration level cooling. The development marks an important step in creating new technologies to replace 100-year-old gas compression refrigeration with solid-state systems up to 30 percent more energy efficient.

Called CaloriSMARTTM – Small Modular Advanced Research-scale Test-station – the system was designed specifically for the rapid evaluation of materials in regenerators without a large investment in time or manufacturing. The initial test subjected a sample of gadolinium to sequential magnetic fields, causing the sample to alternate between heating up and cooling down. Using precisely timed pumps to circulate water during those heating and cooling cycles, the system demonstrated sustained cooling power of about 10 watts, with a 15 degree Celsius (just under 30° F) gradient between the hot and cold ends using only about three cubic centimeters of gadolinium.

“Despite predictions we would fail because of anticipated inefficiencies and losses, we always believed it would work,” said CaloriCool® project director and Ames Laboratory scientist Vitalij Pecharsky, “but we were pleasantly surprised by just how well it worked. It’s a remarkable system and it performs exceptionally well. Magnetic refrigeration near room temperature has been broadly researched for 20 years, but this is one of the best systems that has been developed.”

Pecharsky credited project scientist Julie Slaughter and her team for designing the system that took roughly five months to build. 3D printing capabilities were used to custom-build the manifold that holds the sample and circulates the fluid that actually harnesses the system’s cooling power. The system also features customized neodymium-iron-boron magnets that deliver a concentrated 1.4 Tesla magnetic field to the sample, and the precision in-line pumping system that circulates the fluid.

“We only need 2-5 cubic centimeters of sample material – in most cases about 15-25 grams,” Slaughter said. “We are setting the benchmark with gadolinium and we know there are other materials that will perform even better. And our system should be scalable (for commercial cooling) in the future.”

“But the main reason we conceived and built CaloriSMART is to accelerate design and development of caloric materials so they can be moved into the manufacturing space at least two to three times faster compared to the 20 or so years it typically takes today,” added Pecharsky, who is also an Anston Marston Distinguished Professor in the Iowa State University Department of Materials Science and Engineering.

The magnetocaloric testing is just the beginning. The plan is to upgrade the system to work with elastocaloric materials – that reversibly heat up and cool down when subjected to cyclic tension or compression – and electrocaloric materials – that do the same when subjected to changing electric field. The system will even operate in a combined-field mode that allows a combination of techniques to be used simultaneously.