Reducing ventilation requirements in semi-closed greenhouses increases water use efficiency

We explore an under-appreciated side effect of semi-closed greenhouses: the ability to recover transpired water, thereby increasing water use efficiency. Semi-closed greenhouses are fit with cooling equipment, to limit natural ventilation requirements for temperature and humidity control. We assess the effect of cooling system capacity on ventilation needs of semi-closed greenhouses under different climate conditions and provide a general framework to evaluate potential water savings using the semi-closed greenhouse concept in different regions. We simulate greenhouse climate and crop yields for various cooling system capacities in Central Europe (The Netherlands) and Mediterranean (Greece and Algeria) by implementing a cooling module into an existing greenhouse model (KASPRO) and validating it using concurrent experimental data. Increasing the capacity of the cooling system has a double effect on water use efficiency (WUE): increase of fruit yield due to improved microclimate and lower water use, due to collection and reuse of vapour condensed in the heat exchanger and, to a lesser extent, lower crop transpiration. Thus WUE is strongly associated to the capacity of the cooling system. Finally, we show that there is a unique relationship between water use efficiency and the coupling of greenhouse environment to the outside air (an indicator of ventilation requirements), for all regions studied. (C) 2015 Elsevier B.V. All rights reserved.