Enhancing Electrocaloric Heat Pump Performance by Over 99% Efficient Power Converters and Offset Fields
Stefan Moench, Richard Reiner, Patrick Waltereit, Christian Molin, W. Gebhardt, D. R. Bach, Roland Binninger, Kilian Bartholomé
Abstract
This work analyzes how an over 99% efficient charging circuit and electrical offset fields enhance the coefficient of performance (COP) of electrocaloric heat pumps, an emerging technology with zero global warming potential. The COP is studied for Carnot-like cycles regarding the material’s permittivity and dissipation factor, and the system’s charging efficiency. Compared to the Carnot limit, a relative material COP of 50.4% is calculated for a lead magnesium niobate (PMN) ceramic, and enhanced to 87.4% by an offset field. The offset avoids high loss at low fields, where the non-linear permittivity-related dissipative loss is highest. A 99.2% efficient gallium nitride half-bridge switched-mode converter is used as charging circuit. Including the charging loss, the calculated relative system COP of 11.9% is significantly enhanced to 28.6% by an offset field. The 0.8% external loss exceeds the material loss (dissipation factor below 0.2%), reducing the system COP from the material COP. Compared to 80% efficient state-of-the-art resonant circuits for electrocalorics, this work’s approach reduced charging loss 20 times. The work contributes to transfer the high COP of electrocaloric materials also to electrocaloric heat pump systems.