The use of forced ventilation for greenhouse cooling and air humidity regulation purposes has been expanded around Mediterranean area. The aim of the present study was the experimental investigation of the variables, as well as their interaction, affecting the air temperature in a fan-ventilated greenhouse. On this purpose, measurements concerning both the greenhouse ventilation rate and climate variables inside and outside the greenhouse (air temperature and solar radiation inside and outside the greenhouse and outside wind speed and direction), were carried out in a multi-span fan-ventilated greenhouse. The greenhouse was cultivated with a rose crop and located near Karditsa, central Greece. The results showed that the difference between inside and outside air temperature was strongly related to the ventilation rate as well as to the incoming solar radiation. This finding allowed suggesting a simplified model of the greenhouse energy balance and finally an equation relating the greenhouse air temperature to the outside climate variables (air temperature, solar radiation and wind speed) and the greenhouse characteristics (cover transmission and ventilation rate). The calibration of the model gave satisfactory results and showed that it could be incorporated in algorithms used for greenhouse climate control and also that it could be used as a functional tool for more accurate estimations of ventilation needs. (c) 2004 Elsevier B.V. All rights reserved.