Modelling the effect of the position of cooling elements on the vertical profile of transpiration in a greenhouse tomato crop

Semi-closed greenhouse management may increase greenhouse productivity. However, it relies on the application of mechanical cooling. Cooling can be applied from above or below the canopy. The positioning of the cooling affects the vertical climate profile in the canopy. In order to determine how this affects the vertical profile of transpiration and crop temperature, in this work we used the energy balance of different crop layers to develop a modified “big leaf” model for its temperature and transpiration. The model was validated with data from a large greenhouse experiment (tomato) where the position of cooling elements and climate set-points ensured different vertical profiles of air properties. In particular, we had the combination of two positions of cooling elements (above and below the crop) and two temperature set-points; and a control (not cooled and naturally ventilated) compartment. For the validation we used measurements of crop temperature at different heights in the canopy and of transpiration of the whole crop. Finally we used the model to determine and discuss the effect of the various types of air conditioning on the vertical profile of transpiration within the crop. The compartment with natural ventilation had the highest simulated transpiration (which agreed with the measurements) and the largest uniformity of distribution of transpiration among layers. The least homogeneous distribution was with the cooling elements below, which had also the smallest total transpiration, which was 95% of the transpiration of the crop cooled from above.