.Greenhouses.Flows.HeatAndVapourTransfer.VentilationRates.NaturalVentilationRate_1 .Greenhouses.Flows.HeatAndVapourTransfer.VentilationRates.NaturalVentilationRate_1The natural ventilation rate due to roof ventilation is described by De Jong (1990):
![[m^3*s^(-1)*m^(-2)]](modelica://Greenhouse/Images/equations/equation-6K5EcVLa.png)
where
(
) is the number of windows per square meter of greenhouse floor,
(
) is the wind driven ventilation,
() is the temperature driven ventilation.
The contribution of the temperature driven vetilation in the total ventilation is small but can be important during nighttime and in winter. It is described by:
![[m^3*s^(-1)*window^(-1)]](modelica://Greenhouse/Images/equations/equation-Uu7SYX78.png)
where
(-) is the discharge coefficient caused by friction in the window opening,
(
) is the length of the window
(
) is the gravitational acceleration,
(
) is the thermal expansion coefficient,
(
) is the temperature difference of the greenhouse air and outside air,
(
) is the height of the front opening of the window (
with 
the window width, 
the roof slope and 
the opening angle of the window).The wind speed driven ventilation is computed differently for vents in the windward side and the leeside side. De Jong used 'Window Functions' to relate the air exhange with the wind speed and the opening of a window. The air exchange is described by:
where
(
) is the opening angle of the leeside ventilators,
(
) is the opening angle of the windward ventilators,
(
) is the surface of a window (
),
(
) is the wind speed.