A design problem was then studied with the help of the CFD method, as a demonstration of its capabilities. The winddiiven ventilation behaviour of a continuous roof ventilator in a twin-span Mediterranean-type greenhouse was investigated. The dependence of the ventilation efficiency of this greenhouse on its length was analysed. Our results lead to the interesting conclusion that greenhouses of this type with length smaller than 50 m have higher ventilation rate. This may be a useful hint for future designs.