DEVELOPMENT AND OPTIMIZATION OF LOW-GWP HEAT PUMP SYSTEMS FOR INDUSTRIAL WOOD DRYING.

Abstract

Wood drying is energy-intensive and important for lumber quality, making it a key target for electrification. This thesis develops a schedule-aware modelling framework for heat-pump-driven wood drying and evaluates it using steady-state experiments. The model links kiln schedule targets to psychrometric states, coil duties, electrical power, and specific moisture extraction rate (SMER), using air-side bypass assumptions and a 10-coefficient heat pump performance representation. Validation against industrial data shows good agreement in moisture content trends and captures declines in drying rate, effectiveness, and SMER over time.

Experiments with a closed-loop facility establish baseline R-134a system performance and assess upgrades including low-GWP refrigerant substitution, resized heat exchangers, an expansion valve, and high-temperature air handling. At 40 °C and 50% RH, the upgraded system increases heating capacity from 5.0 to 6.3 kW and SMER from 1.65 to 1.8. Results show broader operating capability, reduced auxiliary heating demand, and improved drying efficiency.