Comparative Computational Fluid Dynamics Analysis of Span-Less and Multi-Span Soilless Greenhouses With Vapor Pressure Deficit Assessment and Experimental Validation

Abstract This study investigates the microclimatic conditions of a Tunisian hydroponic greenhouse using computational fluid dynamics (CFD) in ansys fluent 16.2, combined with experimental validation. Numerical simulations assessed the impact of span configurations on indoor thermal behavior, including temperature, airflow, and solar irradiation. A notable increase of 10.5 K inside the greenhouse compared to ambient conditions highlights the strong influence of structural and crop-related factors on the internal climate. The six-span greenhouse exhibited compartmentalized thermal zones with temperature differences of up to 2 K across planes, providing flexibility for multi-crop cultivation but reducing overall uniformity. In this configuration, average vertical temperatures were higher at y = 9.6 m and y = 14.4 m, while airflow velocities ranged from 0 to 0.5 m · s−1, increasing near exhaust fans. The structural divisions also acted as thermal barriers, shaping airflow circulation and light distribution, with implications for photosynthetic efficiency and crop management. In contrast, the zero-span greenhouse maintained more uniform thermal and airflow conditions with smoother gradients, making it better suited for crops requiring homogeneous environments. Overall, the six-span configuration supported stable temperature and vapor pressure deficit (VPD) conditions favorable for tomatoes and basil, while the zero-span design offered consistent microclimates across the entire growing space. These findings provide practical guidance for optimizing greenhouse design, enhancing microclimate control, and improving agricultural productivity in comparable climatic regions.