Development of an Innovative Defrosting System for Commercial Chiller Evaporators Through Piezoelectric Elements Application

The present study relates to the design of an innovative defrosting system for commercial chiller evaporators. This system is based on piezoelectric plates connected to the evaporator fins and driven at ultrasonic frequencies by a suitable electronic circuit. The operational frequency of piezoelectric elements is chosen to be close to the first harmonics of the fin resonance frequency in the ultrasonic range. The electronic driving system supplies the electric voltage required at the operational frequency starting from the PVM 0–5V signal output of a microcontroller. Moreover, the measurement of the absorbed current is acquired by the microcontroller as feedback to tune the operational frequency at the variation of the fin mass due to frost deposit and detachment. Experimental results show that the approach inhibits the frost deposit during chiller operation, increasing the period between two consecutive defrosting phases which currently is typically no greater than 6 hours. This is an important result considering that while defrosting the chiller must be shut off, depending on the defrosting methods applied, with negative effects on the goods being preserved. The system was developed in collaboration of ISA S.p.A and patented [1].Copyright © 2004 by ASME