This paper presents the results of the simulation of the temperature and air humidity distributions in a 960 m2 semi closed greenhouse with a tomato crop and equipped with fourteen air cooling and dehumidifying ducts. These units are distributed between the crop rows and the sucking inlets are alternately located at high or low locations. The computational model of the aerial domain was developed using the Fluent Computational Fluid Dynamics code. For simulating radiative exchanges, a Discrete Ordinates (DO) model was considered. Sensible, latent and radiative heat transfers together with crop activity (stomatal resistance) and induced water vapour transfers were computed within the crop stands using a porous and semi-transparent medium model. In order to limit both computing time and mesh size, the geometric domain was limited to the greenhouse walls. Experimental conditions for temperature and humidity conditions were applied to the outlets of the ducts. Air leakages and airflow through the vents during the opening period were simulated with sink terms located on the mesh connected with the roof and the walls. Simulations were performed for a single summer day from 8:00 am to 22:00 pm with a 30 min. time step. A new set of boundary values was applied before each simulation. Simulated and measured values of temperature and water vapour concentration inside the greenhouse are presented and commented together with a sensibility study on the influence of the air conditioning device.