Airflow and temperature patterns induced by natural convection were characterized in a 1/2 scale modelmono-span greenhouse model simulating the absorption of solar radiation at the floor surface. Temperatures were studiedby means of thermocouples and airflows by means of hot wire anemometry. The main features of the temperature and flowpatterns were observed in permanent regime for Grashof numbers based on the .T between inside and outside and on thewidth of the opening, ranging from 106 to 107. With a single sided vent situated on the roof, inflows at the lower part of theopening were always observed, and a single airflow loop which followed the walls, the floor and the roof of thegreenhouse before escaping through the upper part of the vent opening. With a two sided vent opening, a singleairflow loop always prevailed with a large recirculation rate, some outside air coming in through the lower parts of theopenings, compensated by air exiting through the upper parts of the same openings. In all situations, thermal gradientsextended over thinner layers (5-6 cm) than velocity gradients (about 50 cm). In these conditions, the vertical temperatureprofile was characterized by a strong temperature drop just above the heated soil surface which represents about 70% ofthe total temperature difference between the soil surface and the outside.<br><br>Values for the ventilation rates were deduced by expressing the thermal balance of the greenhouse and compared withthose deduced from Bernoullis theorem. More generally, the measured flow patterns were compared with those reportedin the literature for ventilation and heat transfers in closed greenhouses. The similitude of the inside patterns observed ineach case suggests that both the exchanges between inside and outside the greenhouse and between the warm soil and theroof can be considered as driving forces influencing the flow.