The main difficulty in the choice of the model is that greenhouse systems cover
a range of length and velocity scales that generally require different modeling
approaches (Bournet and Boulard 2010).
12.4.6 Humidity
Roy and Boulard (2005) simulated wind directions of 0, 45, and 90° with respect to
the orientation of the greenhouse to determine wind speed, temperature, and
humidity distributions inside the greenhouse, getting a good approximation for the
humidity. In agreement with Demrati et al. (2001), models allow estimation, with
better accuracy of water requirements for a banana crop under cover and improved
water saving in regions where water is the main limiting factor for agriculture. Roy
et al. (2008) studied moisture on the surface of leaves at low light levels; crop
transpiration and airflow were integrated into a single parameter model of leaf
stomatal response to airflow and radiation. Campen (2008) showed that climate
through a ventilation system is more homogeneous and the control is more efficient
than with the conventional method of steam extraction. Dehumidifiers and cooling
reduce the overall difference in humidity between the middle and lower areas of a
greenhouse, as demonstrated by Kim et al. (2008) who used a 3D model to identify
the heterogeneous distribution of relative humidity in a greenhouse. According to
Majdobi et al. (2009), an increase in air temperature precedes a more moderate
increase in specific humidity.
12.4.7 Incorporation Crop Effects and Crop Modeling
The effect of plants on greenhouse ventilation has also been studied in the past. For
instance, Bournet and Ould Khaoua (2007), assumed that a crop of 90 cm high and
low density decreases between 12 and 15 % greenhouse ventilation. Dayan et al.
(2004) built a representative model of a greenhouse for three vertical segments,
horizontally oriented to the directions of energy and vapor transfer between the
segments containing plants, considering the external environment. They concluded
that Representative Plant Temperatures (RPTs) can be calculated instead of
measured. Roy and Boulard (2005) developed a 3D model for the characterization
of climatic conditions in a greenhouse, incorporating five rows of ripe tomatoes as
a porous medium where the buoyancy, heat, and moisture transfer between the
crop and airflow inside were considered. The heat and moisture transfer coefficients are deduced from the characteristics of the laminar boundary layer of the
leaf, which are calculated with the velocity of flow in the crop. Khaoua et al.
(2006) found that under external conditions of 1 m s
-1 air velocity and 30° of
temperature, wind speed at crops’ height vary according to the modalities of
ventilation from the windward 0.1 and 0.5 m s
-1 for the leeward side, while
12 Advances in Computational Fluid Dynamics Applied to Biosystems
353
a range of length and velocity scales that generally require different modeling
approaches (Bournet and Boulard 2010).
12.4.6 Humidity
Roy and Boulard (2005) simulated wind directions of 0, 45, and 90° with respect to
the orientation of the greenhouse to determine wind speed, temperature, and
humidity distributions inside the greenhouse, getting a good approximation for the
humidity. In agreement with Demrati et al. (2001), models allow estimation, with
better accuracy of water requirements for a banana crop under cover and improved
water saving in regions where water is the main limiting factor for agriculture. Roy
et al. (2008) studied moisture on the surface of leaves at low light levels; crop
transpiration and airflow were integrated into a single parameter model of leaf
stomatal response to airflow and radiation. Campen (2008) showed that climate
through a ventilation system is more homogeneous and the control is more efficient
than with the conventional method of steam extraction. Dehumidifiers and cooling
reduce the overall difference in humidity between the middle and lower areas of a
greenhouse, as demonstrated by Kim et al. (2008) who used a 3D model to identify
the heterogeneous distribution of relative humidity in a greenhouse. According to
Majdobi et al. (2009), an increase in air temperature precedes a more moderate
increase in specific humidity.
12.4.7 Incorporation Crop Effects and Crop Modeling
The effect of plants on greenhouse ventilation has also been studied in the past. For
instance, Bournet and Ould Khaoua (2007), assumed that a crop of 90 cm high and
low density decreases between 12 and 15 % greenhouse ventilation. Dayan et al.
(2004) built a representative model of a greenhouse for three vertical segments,
horizontally oriented to the directions of energy and vapor transfer between the
segments containing plants, considering the external environment. They concluded
that Representative Plant Temperatures (RPTs) can be calculated instead of
measured. Roy and Boulard (2005) developed a 3D model for the characterization
of climatic conditions in a greenhouse, incorporating five rows of ripe tomatoes as
a porous medium where the buoyancy, heat, and moisture transfer between the
crop and airflow inside were considered. The heat and moisture transfer coefficients are deduced from the characteristics of the laminar boundary layer of the
leaf, which are calculated with the velocity of flow in the crop. Khaoua et al.
(2006) found that under external conditions of 1 m s
-1 air velocity and 30° of
temperature, wind speed at crops’ height vary according to the modalities of
ventilation from the windward 0.1 and 0.5 m s
-1 for the leeward side, while
12 Advances in Computational Fluid Dynamics Applied to Biosystems
353