Use of model-artificial leaves for monitoring aerodynamic conductance in greenhouses

Improving the design, control and management of greenhouse ventilation systems requires a better comprehension of the coupling and feedback mechanisms between the crop, the internal climate and the outside climate. The objective of this work was to characterize the leaf boundary-layer conductance (g b) under greenhouse conditions and to study its dependence on ventilation rate and outside conditions. For this purpose, continuous estimation of gb was carried out in a greenhouse cultivated with rose plants, using rose leaf replicas consisting of a pair of model artificial leaves, one being heated and the other unheated. The boundary layer conductance was derived from the energy balance of the pair of model leaves. Inside air velocity measurements were made by means of a 3-D sonic anemometer. The analysis of the data indicated that, for a given vent aperture and wind direction, there is a clear link between gb and the outside wind speed, and therefore between gb and the ventilation conductance. This relation can be described by a simple linear function in the conditions of our experiments. Using this function for expressing the global greenhouse conductance as a function of the leaf area index allowed getting a better insight on the coupling between the crop and the outside climate. The results also confirm that this model sensor (artificial leaves) might have potential applications in the evaluation of the ventilation performances, as well as in greenhouse climate control and management