Thermal behaviour of a tunnel arc greenhouse during a solar day

Abstract

The present study investigates numerically the effect of transient solar radiation distribution during day-time in arc type tunnel greenhouse with continuous side vents and a tomato crop using a commercial CFD code. A two dimensional mesh was used to render the geometry of greenhouse's section, and the finite volume method was adopted to carry out the fully elliptic partial differential equations' problem. The variation of solar incident radiation during the period of a typical day was incorporated as time dependent boundary condition using an external user defined function (UDF). Optical properties of the covering material were defined according to the wave-length of the incoming solar radiation for three spectral areas (UV, PAR and near infrared). Unsteady computations were performed using an appropriate and constant time step in order to ensure the numerical stability for time discretization with a 2nd order scheme for time evolution. The greenhouse thermal pattern is given in terms of velocity and temperature contours. The results of the present study take under consideration the temporal heat diffusion which leads to heat storage and in different results from the steady simulations. The results show that the temperature pattern inside the greenhouse is a combination of the convective flow and the transient radiative heat transfer during a day time.