Fraunhofer institutes developing electrocaloric solid-state heat pump without compressors

Six Fraunhofer institutes are developing new electrocaloric heat pumps that use elastocaloric heat pipes instead of compressors to extract heat from the sources. The first pilot systems developed by the research team achieved an electrical efficiency of 99.74%.

Germany's Fraunhofer Institute for Physical Measurement Techniques (Fraunhofer IPM) is developing new solid-state heat pumps that do not utilize compressors and are reportedly more efficient than compressor-based counterparts.

In conventional heat pumps, compressors move the refrigerant through the refrigeration cycle and the heat exchanger to extract heat from the source. Rotary and scroll compressors are commonly utilized in commercially available heat pumps. The researchers utilized, instead, active elastocaloric heat pipes (AEH) to enhance the heat transfer rate and achieve latent heat transfer through the evaporation and condensation of the fluid on the caloric material, with ethanol and water being used as fuels.

“The approach based on heat pipes makes for considerably faster cycle frequencies than conventional active pumping of a liquid,” they explained. “The liquid should evaporate and condense on the surface of the electrocaloric material up to ten times per second. This allows a lot of heat to be transported using little material, making it possible to build particularly cost-efficient systems in the future.”

The research team also utilized super-hydrophilic layers developed by the Fraunhofer Institute for Electron Beam and Plasma Technology (Fraunhofer FEP) to make evaporation from the surface particularly efficient and a process to embed the electrodes of the electrocaloric segments in epoxy resin, which was developed by the Fraunhofer Institute for Structural Durability and System Reliability (Fraunhofer LFB), to prevent electrical breakdowns.

Moreover, researchers from the Fraunhofer Institute for Applied Solid State Physics (Fraunhofer IAF) designed a multilevel DC/DC converter based on gallium nitride (GaN) to improve the heat pumps' electrical controls. The device reportedly helped the system achieve an electrical efficiency of 99.74%, a value that is said to set new global standards in conversion efficiency, as efficiency previously stood below 90%.

“Across three different demonstrator systems, the researchers showed that all the components function together, achieving the expected system performance,” the Fraunhofer ISE said, without providing more details on the pilot schemes. “According to simulations, the efficiency of electrocaloric heat pumps with today’s materials is already equal to that of compressor systems.”

The new technology is part of ElKaWe, short for electrocaloric heat pumps research, a research collaboration of six Fraunhofer Institutes under the direction of Fraunhofer IPM.

“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 project manager Kilian Bartholomé of Fraunhofer IPM.