Researchers at Fraunhofer have made significant progress in the development of solid-state heat pumps that operate without compressors. As part of the recently completed ElKaWe research project, a team from six Fraunhofer institutes worked on electrocaloric heat pump technology, focusing on material innovation, system design, and heat transfer efficiency. The project culminated in the creation of three demonstrator systems showcasing the potential of this technology.
Electrocaloric Materials: Key to Efficiency and Durability
Electrocaloric materials are central to the efficiency and durability of these heat pumps. The Fraunhofer IAP team developed thin polymer films with high dielectric strength, forming multilayer components that set new international standards. Meanwhile, Fraunhofer IKTS created ceramic multilayer components using PMN-PT (lead magnesium niobate/lead titanate), which proved highly stable in initial long-term tests, showing no degradation after 70 million cycles. The project also explored lead-free barium-strontium-stannate-titanate (BSSnT) as a promising material compliant with RoHS guidelines.
Fast Heat Transfer Without Harmful Refrigerants
One of the main challenges for electrocaloric heat pumps has been heat dissipation. To address this, researchers employed active elastocaloric heat pipes (AEH) that use ethanol and water as working fluids, providing an environmentally friendly alternative to traditional refrigerants. Fraunhofer IPM integrated a patented AEH design into an electrocaloric system, enabling faster cycle frequencies—up to ten cycles per second—allowing for efficient heat transport with minimal material use. Additionally, Fraunhofer FEP developed super-hydrophilic coatings to enhance evaporation, while Fraunhofer LBF embedded electrodes in epoxy resin to prevent electrical breakdowns.
High-Efficiency Electrical Controls
Efficient electrical control is crucial for electrocaloric heat pumps. Fraunhofer IAF designed a GaN-based multilevel DC/DC converter with a 99.74% electrical efficiency, surpassing the previous benchmark of 90%. This advancement contributes to the overall performance and energy efficiency of the system.
Demonstrators Show Promise for Marketability
The research team successfully integrated these components into three different demonstrator systems, achieving expected performance levels. Simulations indicate that electrocaloric heat pumps with current materials already match the efficiency of traditional compressor-based systems, with potential for further improvement. "ElKaWe has generated a leap forward in terms of material, electronic components, and heat transfer. While we still have a long way to go, these advances are promising steps towards marketability," said Dr. Kilian Bartholomé of Fraunhofer IPM.
Christian Vogel, a member of the project advisory committee, emphasized the significance of the work, stating, "The interdisciplinary team worked together extremely well, solving key questions. The great potential of electrocaloric technology was clearly demonstrated."
With continued research and development, electrocaloric heat pumps could offer a more efficient and environmentally friendly alternative to traditional heating and cooling systems.
