| The ventilation of a two-dimensional four and one-half span greenhouse with roof vents and side vent and bench grown potted plants was simulated in a computational fluid dynamics (CFD) numerical model. The greenhouse was designed with a windward side vent and leeward roof vents for achieving maximum ventilation with a west wind. The volumetric flow rates and the air exchange rates from the CFD model were compared to a control volume energy balance model to investigate the validity of the CFD model. Environmental data were collected inside and outside the simulated double polyethylene, commercial greenhouse and used in the models. While good agreement was obtained between predicted values from the models, the results showed mostly negative errors in the morning and positive errors in the afternoon due to heat storage in the floor, benches, and framing of the multispan greenhouse. The most significant factor for the CFD model was the wind speed with a correlation coefficient of 0.967 and for the energy balance model was solar radiation at 0.814.; The maximum recorded air temperature difference between inside and outside the greenhouse was 3.51{dollar}spcirc{dollar}C during the hottest (34.7{dollar}spcirc{dollar}C) recorded sunny day. The air temperatures within the greenhouse were very uniform with the maximum difference between six inside air temperatures being 1.67{dollar}spcirc{dollar}C.; The CFD predicted results showed that the wind speed, wind direction, vent opening sizes, and the presence of plants and benches all affected natural ventilation. The effect of the side vent opening size was not significant when the roof vents were totally closed. The side vent and fourth roof vent had the highest volumetric flow rates among all vent openings. The CFD predicted results also showed that, during data collection, the average, minimum, and maximum air change rates in the greenhouse were 1.157 A.C./min, 0.364 AC./min, and 2.661, respectively with the west wind and they were 0.636 A.C./min, 0.124 A.C./min, and 1.675 A.C./min, respectively with the east wind. The plants and benches slightly modified the natural air exchange in the greenhouse and slightly decreased the total predicted air exchange by 12.0%. |
