An energy-efficient multi-drying-chamber-based heat pump wood drying system.

The lumber industry is a carbon-intense industry that relies on the combustion of fossil fuels for wood drying. Heat pumps offer an efficient, electrically-driven alternative for the process heating in wood drying systems, though a unique system design is required to achieve substantial energy savings. In this work, we present a theoretical model for single-effect and two-effect heat pump wood drying systems, where the two-effect system recovers heat from one drying chamber and uses that heat to run a second drying chamber. Various low global warming potential (GWP) and natural refrigerants are evaluated, with propane standing out as the most advantageous. Under nominal conditions, the two-effect system could achieve a specific moisture extraction ratio (SMER) of up to 11 kg/kWh for an ideal dryer and an SMER of 4.5 kg/kWh under more practical conditions. The two-effect system achieves an SMER nearly two times that of the single-effect dryer.