Computational fluid dynamic modeling to improve the design of the Spanish parral style greenhouse

The Parral greenhouse is a simple, low cost, naturally ventilated structure that is very common around the Mediterranean Sea for production of vegetables. Natural ventilation is by roof vents that are covered with either a rolling cover or flap cover. Some also use limited sidewall openings. Their designs limit air exchange which results in high summer temperatures that create major heat stress to the plants. Computational Fluid Dynamic (CFD) models to numerically solve the continuity and momentum equations for the greenhouses were developed to study alternative designs. The models were verified against existing tracer gas data. The models were two-dimensional, steady state using either the standard kappa - epsilon or the renormalization group (RNG) viscosity models. The results for the airflow through the vent openings and the actual vent opening areas were used to calculate air exchange rates for wind speeds of 2, 3, 4, and 5 in s(-1). These results compare favorable to earlier tracer gas measurements. The choice of viscosity model was critical when the rolling flap cover was on the windward roof. Using the model, the effects of steeper roof slopes were evaluated. At wind velocities of 2 in s(-1) or less, the roof slope had very little effect. At higher wind speeds, the air exchange rate increased with roof slope. Increasing the roof slope above 27 degrees provided minimal additional air exchange rate.