Analysis of Greenhouse Ventilation Efficiency based on Computational Fluid Dynamics

摘要

The effect of wind speed and roof vent opening configuration on airflow and temperature patterns in a compartmentalised glasshouse was numerically analysed by means of two-dimensional computational fluid dynamics (CFD). The numerical model was first successfully validated against ventilation rate data collected in a 2600 m{sup}2 four-span glasshouse divided into two compartments separated by a plastic partition. The model was later used to study the consequences of three different opening configurations on the natural ventilation in a compartmentalised glasshouse with only windward or leeward roof vents, or a combination of both. The ventilation process was assessed on the basis of the estimation of the ventilation rate, which is often considered as crucial, and the analysis of the distributed climate inside the greenhouse. This study was completed by considering the velocity and temperature profiles at plant level (1 m), i.e., where the physiological mechanisms controlling plant growth take place. Results show that opening configurations combined with wind speeds strongly affect inside ventilation and microclimate parameters. Moreover, inside partition hinders the air circulation between the different parts and causes significantly different internal microclimates within each compartment. Thus, for an outside wind speed and air temperature of 1 ms{sup}(-1) and 30℃, respectively, computed ventilation rates varied from 9 to 26.5 air changes per hour in the windward compartment and from 3.7 to 12.5 air exchange per hour in the leeward one. Likewise, under the same conditions, simulations showed that air velocity at crop cover level varied according to vent arrangements and compartment positions from 0.1 to 0.5 ms{sup}(-1), whereas temperature differences varied from 2 to 6℃. This study also showed that other parameters such as climate heterogeneity must be investigated in order to define the best ventilation configuration, and that temperature and velocity rises at crop level can be balanced by opening both windward and leeward roof vents.