Experimental and numerical study of heat and mass transfer occurring at plant level inside a greenhouse

Over the past two decades, the modelling of greenhouse climate with CFD techniques mainly focussed on the understanding of the physical behaviour of greenhouses (ventilation, light transmission). Only few numerical CFD studies however, properly describe the interaction of the crop with the local climate and most authors have to cope with a lack of data for validation. The impact of the crop on the climate may be significant as it is known to slow the flow and to exchange heat and mass (water vapour) with the inside ambient air. The present study aims at validating numerical simulations on the basis of both latent and sensible heat transfers occurring at plant level and considering the major climatic/physical components which govern these exchange processes (such as the leaf temperature, or the stomatal and aerodynamic resistances). Experiments were conducted in a 100-m2 greenhouse compartment. Potted impatiens plants growing on shelves were considered. A set of sensors including a sonic anemometer, thermocouples, air-humidity/temperature probes, pyranometers, pyrradiometers and balances was used to assess the greenhouse micrometeorology and to estimate the heat and mass transfers from the canopy. Two-dimensional simulations were carried out with a computational fluid dynamics software. The calculation domain reduced to a parallelepipedic shape including the plants. The Navier-Stokes equations were solved using the standard k-ε turbulence model and a radiative submodel was activated. A porous medium model (Darcy Forchheimer) was adopted for the crop and a specific routine was developed to take account of latent and sensible heat transfers. Comparison with experimental data provided reasonable agreement for the air and leaf temperatures in particular. Even if some discrepancies remain, the modelling approach appears to be a useful tool to predict the impact of the canopy on the local climate inside the greenhouse.