.Greenhouses.Flows.HeatAndVapourTransfer.VentilationRates.ForcedVentilationRate .Greenhouses.Flows.HeatAndVapourTransfer.VentilationRates.ForcedVentilationRateThe natural ventilation rate due to roof ventilation is described by Boulard and Baille (1995):
where
(-) is the control of the aperture of the roof vents,
(
) is the maximum roof ventilation area,
() is the greenhouse floor area,
(-) is the discharge coefficient which depends on the greenhouse shape and on the use of an outdoor thermal screen,
(
) is the gravitational acceleration,
(
) is the vertical dimension of a single ventilation opening,
(
) is the mean temperature of the greenhouse air and outside air,
(-) is the global wind pressure coefficient which depends on the greenhouse shape and on the use of an outdoor thermal screen,
(
) is the wind speed.Since it is considered that the greenhouse does not have side vents, the whole ventilation rate is through the roof vents.
The discharge coefficients 
and 
depend on the use of an external shading screen. However, it is considered that in the studied greenhouse there is no external shading screen.