Numerical prediction of the effect of vent arrangements on the ventilation and energy transfer in a multi-span glasshouse using a bi-band radiation model

The distributed climate inside a greenhouse mainly results from mass, momentum and energy transfers occurring through the openings or through the cover. These transfers can be assessed using computational fluid dynamics (CFD) techniques. However, to date very few studies considered properly the radiative exchanges between the surfaces inside the calculation domain by solving simultaneously the radiative transfer equation (RTE) and the convective ones. The object of this work is to implement this equation in order to get an overview of the resulting climate inside the greenhouse. The analysis focuses on the heterogeneity of the climatic parameters in the canopy vicinity as well as on the ventilation rate. For the purpose of the study, a two-dimensional steady-state CFD model was developed. It is based on the resolution of the Navier-Stokes equations with the Boussinesq assumption and a k-epsilon closure. Solar and atmospheric radiations were included by solving the RTE and distinguishing short [0-3 mu m] and long wavelength [3-100 mu m] contributions. The virtual tracer gas technique was implemented to assess the ventilation rate. The model was first successfully validated against experimental data considering a glasshouse divided into two compartments separated by a plastic partition and comparing simulated and recorded temperatures inside the shelter and along the walls (roof and sides). Simulations were then carried out for a 2500 m(2) four-span sloped-roof glasshouse covered with a 4-mm-thick horticulture glass and equipped with continuous roof vents and one side-opening. Results show that roof-opening configurations combined with side-vent location strongly affect inside ventilation and microclimate parameters. Thus, for hot summer conditions with relatively low wind, computed ventilation rates varied from 2 to 40 air changes per hour whereas temperature differences varied from 3 to 13 degrees C. This study also showed that other characteristics such as climate heterogeneity must be investigated in order to define the best ventilation configuration and that strong velocity and temperature heterogeneity can occur at the plant level. Simulations, however, suggest that the symmetric roof-vent configuration seems to be a good compromise between cooling and homogeneity performances. (C) 2007 IAgrE. Published by Elsevier Ltd. All rights reserved.