The seawater greenhouse in the United Arab Emirates: Thermal modelling and evaluation of design options

Abstract

The Seawater Greenhouse combines a solar desalination system with an environment for cultivating crops in which transpiration is minimised. Results from the prototype greenhouse in the United Arab Emirates (UAE) are used to calibrate a computational fluid dynamic (CFD) model. With the UAE design taken as a baseline, the model is used to evaluate three proposed options for improving performance. These differ with respect to how the plants are shaded and how air flows through the greenhouse. In the baseline design, a semi-opaque plastic sheet is used to provide shade. The first option uses a similar sheet; however the air flows in a C-shaped path, travelling in opposite directions above and below the sheet. The second option uses a perforated sheet through which air is drawn. In the third option, an array of plastic pipes carrying seawater provides shade. The warmed seawater from the pipes is fed into the back evaporator to boost fresh water production. We present results for freshwater production, evapotranspiration and temperatures inside the greenhouse, covering a range of ventilation airflows. The first option gives only marginal improvements in freshwater production and cooling. In contrast, the second option significantly increases water production. Air temperature in the greenhouse increases, whereas the mean radiant temperature decreases. The third option gives the greatest increase in water production in addition to slightly lower air temperature in the greenhouse and significantly lower mean radiant temperature. Evapotranspiration varied little over all the cases studied. The reasons for these findings and their implications for the design of the system are discussed.