Analysis of Climate Uniformity in a Naturally Ventilated Greenhouse Equipped with High Pressure Fogging System Using Computational Fluid Dynamics

High pressure fogging systems and control strategies in naturally ventilated (NV) greenhouses has been investigated as an alternative cooling mechanism to mechanical ventilation systems with aims of saving energy and water and potentially helping to improve climate uniformity in the greenhouse. Studies on analyzing the climate uniformity under NV with fogging, including the analysis of greenhouse aerodynamics, climate uniformity lacks. A 3D Computational Fluid Dynamics (CFD) analysis was used to simulate environment conditions of a NV greenhouse equipped with high pressure fogging. The study utilized models including porous media to simulate crop canopy, the Solar Load model and the Discrete Ordinates radiation model to simulate solar radiation, the species transport and the discrete phase to simulate evaporation of droplets and evapotranspiration. Experimental data collected from a single-span greenhouse was used to validate combined model. Simulated environmental variables are compared between a scenario with fogging activated and the same scenario without fogging. The simulated temperature and relative humidity at 21 points were compared to corresponding experimental measurements with percentage errors of 6-16% and 14-27%, respectively (99% confidence). There were no statistically significant differences between the simulated and experimental data sets determined by ANOVA (alpha=0.1). The results showed that there is a significant effect of fogging on temperature and VPD uniformity. In addition, it was shown that the air flow pattern had a significant effect on the internal environmental variables. The positions and angels of the fogging nozzle affected the interior climate.