Technical, energy, and environmental performance evaluation of an industrial-scale solar–steam hybrid wood drying system in tropical climate of Vietnam

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Abstract

This study presents an industrial-scale evaluation of a 100 m³ per batch solar–steam hybrid wood drying system operating under tropical climate conditions in Vietnam. A full drying cycle of approximately 480 hours was performed on 13-mm Acacia mangium lumber using a multi-point monitoring system that recorded dry- and wetbulb temperatures, relative humidity, air velocity, solar irradiance, and the thermal and electrical energy inputs at 10-minute intervals. The integrated roof collector achieved an average thermal efficiency of ~46 % (peaking at ~52 %), delivering 15,687 kWh of useful heat and supplying 40 – 52 % of the daytime thermal demand. Compared with a conventional steam kiln, the hybrid system reduced biomass consumption by 50 %, electricity use by 34.3 %, and total energy input by 45.2 %. The Specific Energy Consumption (SEC) decreased from 1.99 to 1.09 kWh/kg of water removed (- 45.2 %), confirming hypothesis H1. The solar fraction reached 44.3 % (thermal basis) and 33.8 % (total basis), supporting hypothesis H3. Wood quality assessments following TCVN 8929/8930 showed that the hybrid kiln maintained comparable levels of product quality, with surface and internal check rates of 2.8 % and 1.0 %, respectively. The average warping was 2.2 mm, exhibiting an improving trend compared with the control kiln (p = 0.054), thereby further supporting hypothesis H2. Environmental analysis following IPCC 2006/2019 guidelines indicated that the hybrid system reduced non-biogenic CO2 emissions by 34.3 %, consistent with hypothesis H4. Overall energy costs decreased by 38.7 % per batch, resulting in a payback period of approximately 3.04 years, which remained below 4 years under CAPEX variations of ± 20 %. Collectively, the findings demonstrate that the solar–steam hybrid system is an efficient, stable, and economically viable solution for industrial wood drying under tropical conditions,contributing to reduced fossil-based CO2 emissions and supporting sustainable production pathways.

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