modelNaturalVentilationRate_1
Air exchange rate from the greenhouse air to the outside air function of wind and temperature by De Jong (1990)
Information
The 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.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Units.SI.Angle | phi | 25/180*Modelica.Constants.pi | inclination of the roof (0 if horizontal, 25 for typical cover) |
| Real | fr_window | 0.078 | number of windows per m2 greenhouse |
| Modelica.Units.SI.Length | l | length of the window | |
| Modelica.Units.SI.Length | h | width of the window | |
| Boolean | thermalScreen | false | presence of a thermal screen in the greenhouse |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Units.SI.Velocity | u | 0 | Wind speed |
| Modelica.Units.SI.Angle | theta_l | 0 | window opening at the leeside side |
| Modelica.Units.SI.Angle | theta_w | 0 | window opening at the windward side |
| Modelica.Units.SI.TemperatureDifference | dT | 10 | |
| Real | f_vent | ||
| Real | f_vent_wind | ||
| Real | f_vent_temp | ||
| Real | C_f | constant of discharge of energy caused by friction in the window opening | |
| Real | beta | thermal expansion coefficient | |
| Real | f_vent_top | Air exchange rate at the top air compartment in presence of a thermal screen | |
| Real | f_vent_air | Air exchange rate at the main air compartment |