Drying Kinetics, Energy Performance, and Quality Characteristics of Kelp Under Hybrid Infrared–Heat Pump Drying

A hybrid infrared (IR)–heat pump (HP) drying system was investigated for vertically suspended kelp under four operating conditions, including infrared drying alone (IR) and three heat pump-assisted drying conditions with low (IR–HP-L), medium (IR–HP-M), and high (IR–HP-H) dehumidification intensities. The effects of heat pump operation on drying kinetics, energy performance, and product quality were evaluated under a fixed nominal infrared power density and airflow condition. The results showed that heat pump integration effectively reduced the humidity of the circulating air and accelerated moisture removal without substantially altering the drying temperature. The drying time decreased from 6.00 h for IR to 5.25, 4.65, and 4.40 h for IR–HP-L, IR–HP-M, and IR–HP-H, respectively. However, the improvement obtained by increasing the heat pump intensity from medium to high was limited compared with the additional compressor energy input. The specific energy consumption (SEC) decreased from 7.46 kWh kg−1 water for IR to 5.82 kWh kg−1 water for IR–HP-M, whereas it increased to 6.05 kWh kg−1 water under IR–HP-H. Thin-layer drying models showed good agreement with the experimental moisture-ratio profiles, and model evaluation indicated that fitting accuracy should be considered together with model complexity. Quality evaluation showed that IR–HP-M provided favorable mean values for color retention, rehydration performance, moisture uniformity, and mechanical characteristics, although the statistical significance of individual quality indicators should be interpreted based on batch-level variability. A comprehensive performance evaluation incorporating drying efficiency, energy utilization, and quality characteristics identified IR–HP-M as a favorable compromise under the tested conditions. Sensitivity analysis further indicated that the preferred operating condition depended on the weighting scheme and normalization method. These results provide experimental evidence for selecting appropriate heat pump dehumidification intensity in infrared-assisted drying of high-moisture sheet-like marine biomass.