.Greenhouses.Flows.HeatAndVapourTransfer.Ventilation .Greenhouses.Flows.HeatAndVapourTransfer.VentilationVentilation replaces greenhouse air by outdoor air. In most cases this exchange is governed by natural ventilation through windows, from which the aperture of the windws is controlled by the greenhouse climate controller. However, since greenhouses are not completely air tight, there is also a small uncontrolable ventilation flux caused by leakage.
The heat transfer between the inside and outside air due to natural ventilation is computed as a function of the air exchange rate by using the NaturalVentilationRate_2 model. This rate, derived by [1], depends mainly on two factors. The first one is the windows opening, a required input which is set by the climate controller. The latter are characteristics of the windows (e.g. the wind pressure coefficient and the coefficient of energy discharge caused by friction at the windows), which in order to simplify the model, have been set to constant values relative to standard roof windows.
If a mechanical ventilation system is installed, the heat flow caused by this system also needs to be taken into acount. The heat flow from forced ventilation is also computed as a function of the air exchange rate, which depends on the capacity of the mechanical ventilation system (parameter of the model) and the position of the control valve (required input set by the climate controller). This computation is done in the ForcedVentilationRate model.
Depending on the status of the thermal screen, the heat flow can originate either from the top or the main air zones. Therefore, the user must indicate which zone is being modeled through a Boolean parameter. The screen closure (control variable from the climate controller) is a required input.
This model also takes into account the leakage rate through the greenhouse structure, which is dependent on the wind speed (input of the model) and the leakage coefficient of the greenhouse (parameter of the model, characteristic of its structure).
[1] T. Boulard and A. Baille. A simple greenhouse climate control model incorporating effects of ventilation and evaporative cooling. Agricultural and Forest Meteorology, 65(3):145–157, August 1993. ISSN 0168-1923. doi:10.1016/0168-1923(93)90001-X.