Intermittent versus continuous kiln drying of hardwood boards: comparable-stage analysis of energy use, kinetics, quality, and climate impacts

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Abstract

Intermittent kiln drying is often proposed as an energy-saving strategy, yet integrated experimental evidence for hardwood boards remains limited. This study developed a laboratory-scale convective kiln and generated an experimental dataset for Tauari lumber ( Couratari stellata ) under four drying treatments combining continuous (T1 and T3) and intermittent (T2 and T4) operation with schedule variants. Drying performance was assessed for two wood batches using stage-resolved moisture removal and process time, while intermittency was quantified through cumulative heating time. Empirical drying kinetics were described by moisture ratio trajectories fitted with a global Page model and complemented by stagewise Lewis constants. Post-drying quality was evaluated through distortions, residual stress, and defect incidence. To ensure comparability, performance indicators were evaluated across common stage windows within each lumber batch. Within these windows, intermittent operation reduced cumulative heating time by 58.3% and 69.9%, while total electrical demand decreased by 9.7% and 14.7% relative to the corresponding continuous treatments. The Page model accurately described moisture ratio evolution (R 2 = 0.983–0.998). Bow was consistently lower under intermittent operation, while other distortions and casehardening showed no significant differences. A gate-to-gate life cycle assessment using 1 kg of removed water as the functional unit showed that climate impacts were dominated by electricity consumption for heating and ventilation. Carbon intensity ranged from 841 to 3016 g CO 2 -eq kg −1 depending on the electricity mix, with intermittent drying consistently presenting the lowest emissions. Overall, intermittent drying reduced active heating demand, electrical consumption, and associated GHG emissions under laboratory-scale conditions, while maintaining overall wood quality with a specific benefit for bow reduction. • Intermittent drying reduced electrical demand by up to 14.7% vs continuous. • Specific energy decreased from 6.27 to 5.32 kWh kg −1 water in Schedule 2.1 • Stagewise analysis revealed strong late-stage penalties in drying energy. • Ventilation share dropped from 39.6% to 14.1% under intermittent drying. • Gate-to-gate LCA quantified climate impacts of kiln drying schedules.

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