A comprehensive review of heat pump wood drying technologies

Wood drying is one of the most energy-intensive processes in lumber production, and most wood drying kilns rely on combustion for the process heating. Heat pumps are a promising technology for electrifying industrial heating processes, including wood drying. However, the application of heat pumps has been limited, largely due to the long-established popularity and cost-effectiveness of combustion-based technologies. While previous reviews have covered wood drying technologies more generally, this paper aims to bridge the gap between the wood drying and heat pump fields that have largely been investigated separately. This paper reviews the current wood drying process, including standard operating procedures, wood properties, and conventional drying kilns. Then, the current state-of-the-art heat pump wood drying technologies are reviewed, including heat pump cycle options, energy recovery, refrigerant selection, component enhancement, controls, and renewable energy integration. Additionally, other electrically driven technologies that can be combined with heat pumps to improve the efficiency and control of wood drying systems are reviewed. As the electrification of wood drying can significantly reduce global carbon emissions, this review article is a strong foundation for developing innovative systems and components for heat pump wood drying.