Reproduction of Vapor Pressure Deficit Control in Sunlight Type Plant Factory Using CFD Analysis

In sunlight type plant factories, VPD (Vapor Pressure Deficit) control using fine mist evaporative cooling has been reported to increase tomato yields by approximately 10-20%. However, due to the semi-closed environment, seasonal environmental fluctuations are significant, and the development of control methods tailored to such variations requires a substantial amount of experimental data obtained under a wide range of environmental conditions. Therefore, in this study, we developed a digital twin system of the sunlight type plant factory using CFD (Computational Fluid Dynamics) simulation, aiming to perform control experiments under various environmental conditions and to acquire abundant experimental data. Specifically, VPD control was reproduced by simulating fine mist evaporation through a combined approach of the finite volume method and particle tracking method. At each control interval, the simulation was paused, the controlled variable was calculated based on reference values within the simulation model, and the mist spraying parameters were updated accordingly before resuming the simulation. Consequently, the developed system made it possible to evaluate and refine VPD control methods under various environmental conditions, while considering the spatial conditions throughout the entire plant factory.