July 24, 2023
Source: Energy & Management Powernews
Fraunhofer researchers are developing electrocaloric heat pumps as an alternative to the currently common compressor technology. They should be more efficient and do without refrigerants.
Heat pumps are considered a central component of the heat transition. To increase the efficiency of heat pumps, researchers from six Fraunhofer institutes are working in the lead project "Electrocaloric Heat Pumps" - short "ElKaWe" - on novel heat pumps, which should allow a particularly efficient heat dissipation and at the same time require neither compressor nor refrigerant. The Fraunhofer Institute for Physical Measurement Techniques IPM is in charge of the project.
About the status quo: Due to their technology, today's heat pumps achieve only about 50 percent of the physical Carnot limit, i.e. the theoretically highest possible efficiency when converting thermal energy into mechanical energy. Electrocaloric heat pumps, on the other hand, achieve 85 percent - at least in theory. But how efficient electrocaloric heat pumps ultimately are also depends largely on the efficiency of the integrated power electronics.
The Fraunhofer Institute for Applied Solid State Physics IAF is responsible for optimizing the power electronics as part of the Elkawe project. It researches devices based on the semiconductor gallium nitride (GaN) to increase power density and efficiency. Now, for the first time, the researchers have developed power electronics specifically for electrocalorics. They have succeeded in implementing an ultra-efficient circuit topology for voltage converters based on GaN transistors, achieving an electrical efficiency of 99.74 percent in the electrical power path. The GaN-based multilevel DC/DC converter, they now announce, far exceeds the previous research level of less than 90 percent conversion efficiency for electrical driving of these novel heat pumps.
Until now, the scientists write, electrocaloric heat pump systems have been limited by electronics losses, for example. The increased electrical efficiency brought about by their development, they say, leads directly to a higher coefficient of performance for the overall heat pump system.
"Our ultra-efficient power electronics make it realistic for the first time to achieve significantly more than 50 percent of the maximum theoretical coefficient of performance with electrocaloric heat pumps, even at the system level," explains Dr. Stefan Mönch of Fraunhofer IAF. While there is still a lot of research to be done, he adds, in the future this technology could become a more efficient and completely emission-free solution for heating and cooling.
The electrocaloric effect
The principle behind the electrocaloric heat pump is formed by the electrocaloric effect: if an electrical voltage is applied to an electrocaloric material made of special ceramics or polymers, the material heats up. As soon as the voltage is removed, the material cools down again, and the entire process is almost completely reversible.
Since electrocaloric materials form an electrical capacitance, the power electronics in the system have the task of electrically charging and discharging the electrocaloric capacitances several times per second as highly efficiently as possible, and thus as losslessly as possible, with heat being pumped in each cycle.
Author: Davina Spohn
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