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May, 2018

The concept of recycling is well known in the context of refuse, but the analogous concept of recycling energy has been hitherto ignored in the context of electrocaloric cooling devices, even though one of the main motivations is to achieve good energy efficiency. These devices are based on ferroelectric capacitors, which typically become hot when charged, and cold when discharged, as a consequence of accessing the entropy associated with the electrically driven ferroelectric phase transition. Each and every cooling cycle necessarily requires the capacitors to be charged and discharged, but until now the capacitors have always been discharged without any attempt to recover any of the electrical energy that they store.

The present paper addresses the issue of energy recovery in three stages. First, it shows that there should be plenty of energy to recover, even after taking into account that perfect recovery is impossible because work must be done to pump heat. Second, it shows that one can recover 80% of the recoverable stored energy when two ferroelectric capacitors transfer charge on demand. Third, it shows that energy recovery can enhance the energy efficiency of a prototype cooling device by a factor of 2.9. The implication is that all electrocaloric cooling devices should in future attempt to recycle and not waste electrical energy. Otherwise they should be binned. Or recycled.

Figure: electrocaloric cooling device based on two plates (12C1 and 12C2) that each comprise twelve multilayer capacitors. The two plates operate in antiphase, and discharge into each other rather than wastefully into a resistor.

E. Defay, G. Despesse, R. Faye, H. Strozyk, D. Sette, S. Crossley, X. Moya and N. D. Mathur, "Enhanced electrocaloric efficiency via energy recovery", Nature Communications 9 (2018) 1827

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