Forced-air cooling of iceberg lettuces: Cooling efficiency in relation to commercial operating strategies

Abstract

Commercial forced-air cooling (FAC) of iceberg lettuce is usually not ideal due to multiple uncontrollable factors in the pre-cooling facility, artificial non-standardized operations and operator experience used to select the pre-cooling time. This study aimed to investigate the cooling efficiency (cooling rate, heat load and energy consumption) during commercial FAC of iceberg lettuce under two kinds of operating mode. Our field studies demonstrated that when pallets were loaded in batches with a 20 min interval (Operation A) better cooling effectiveness and less energy consumption was achieved in comparison to when all pallets were loaded and pre-cooled simultaneously (Operation B). The seven-eighths cooling time (SECT) of pallets with the lowest cooling rate in the Operation A (227 min) and Operation B (325 min) were reduced by 43.2 % and 18.8 %, respectively, compared to worker experience estimated time (400 min). In addition, the heat load analysis results indicated that Operation A was an effective way to achieve the goal of enhancing the energy efficiency of the refrigeration unit and keeping the compressor operating under the design condition.