CONSERVING ENERGY IN BLAST FREEZERS USING VARIABLE FREQUENCY DRIVES

摘要

A stationary blast freezer processing 22-lb cartons of sardines in 19,000 pound lots was modified to improve efficiency and to conserve energy. Baffles were first added to produce uniform air flow. Maximum measured freeze times of 12.6 hours fell to 10.5 hours; total electrical energy savings was estimated to be 12%. A Variable Frequency Drive (VFD) was then installed to slow evaporator fans during the freeze cycle. In one example run when fans were slowed to 75% speed after an initial freezing period, freezing times then increased by about an hour while overall energy consumed fell by an additional 10%. Based on the effect of the VFD alone and $0.05/kWh power in this case, payback period would be in the range of 850 freezing cycles. Mathematical models, calibrated by measurements, analyzed further design and fan control options. Further improvements in freezing efficiency were predicted.