Solar radiation distribution in a tunnel greenhouse

Abstract

A commercial computational fluid dynamics code was used in order to investigate numerically the effect of solar radiation in an arc type tunnel greenhouse equipped with continuous side vents with a tomato crop. For the simulation's needs a two dimensional mesh was used to render the former geometry, and the finite volume method was adopted to carry out the fully elliptic partial differential equations' problem. Climatic data provided by the Greek Centre of Renewable Energy Sources were used in order to approach realistic conditions. Special items like the mechanical behaviour of the covering material or the climatic behaviour of the rows of the tomato crop are taken into account using external user defined functions (UDF). Optical properties of the tested covering materials were defined according to the wave-length of the incoming solar radiation and three spectral areas (UV, PAR and near infrared). Based on the meteorological data of October for the region of Volos (Greece), two parametric studies were carried out concerning different angles of the incoming solar radiation and the different optical properties of the covering materials. Results show the influence of the optical properties of the covering materials and of the incidence angle of the incoming solar radiation on the distribution of solar radiation inside the greenhouse. The flow recirculation due to buoyancy effect shows the importance of internal temperature gradients although the dominance of the forced convection resulting from natural ventilation. The diversification of the temperature patterns, mainly and secondarily of the airflow field indicates that heat transfer due to the solar radiation distribution for different covering materials in the three different spectral areas was successfully simulated.