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InverSim A Simulation Model for
Greenhouse   C.A. Bouzo, N.F. Gariglio, R.A.
Pilatti, D.A. Grenón, J.C. Favaro, E.R. Bouchet
and C. Freyre Kreder 2805, S3080HOF
ESPERANZA, Santa Fe, Argentine TE
54-3496-420639. cbouzo_at_arnet.com.ar
Universidad Nacional del Litoral Facultad de
Ciencias Agrarias Departamento de Producción
Vegetal
INTRODUCTION
RESULTS
The Argentine central region stands out for a
tempered weather which causes considerable yield
losses and quality problems for most greenhouse
crops during the warm season. In that case, the
knowledge of the greenhouse climate is essential
to improve the design of structures as well as
the environmental control and management (van
Henten and Bontsema, 1996). Cooling the
greenhouse through natural ventilation is a cheap
alternative for the greenhouse located in warm
climates, but this technique is insufficient to
achieve climatic conditions compatible with the
crops requirements during the warmest months,
when high radiation loads and high temperature
slowed down the yield and the quality of the
production (Hanan, 1997). Ventilation allows the
exchange of energy and mass to take place between
the greenhouse volume and the outside environment
(Kittas et al., 2003). Considering the greenhouse
as a solar collector, its behaviour can be
modelled through the use of a single-energy
balance equation (Boulard and Baille, 1993).
Figure 3. Daily trend of the calculated values of
the air temperature by the InverSim model
and of measured values given by seven sensors
located inside the greenhouse.
AIM
Develop a model aimed to describe the dynamic
behaviour of air temperature and humidity inside
the greenhouse.
MATERIALS AND METHODS
Theory The greenhouse thermal behaviour during
day time is described by means of a simplified
energy balance equation
(1)
The first three terms of Eqn. (1) respectively
represent the greenhouse radiative gain and the
sensible and latent heat exchange by ventilation
(Boulard and Baille, 1993). The fourth term
represents the overall sensible heat transfer at
the cover surface and includes the convective and
radiative (thermal) losses. The water vapour
balance is calculated by the following formula,
modified according to Jolliet (1994), in which
the soil evaporation rate and the condensation
rate at the inner face of the greenhouse cover
are neglected. Crop transpiration (lEt, W
m-2), which was calculated by Combining
equations (1), (2) and (3), we obtain a
two-equation system with two unknown variables,
which allow us to estimate the gradients between
the inside and the outside of the greenhouse, for
water vapour (?e) and air temperature (?T).
Experimental set up To validate the
model a greenhouse with metallic structure
(Figure 1 and 2) was used (ADC Greenhouses) in
Santa Fe, Argentine (31 30' S, 62 15' W). Seven
sensors were placed inside the greenhouse at 2 m
above ground in order to measure the air
temperature (C) and the relative humidity (),
through a weather automatic station LiCor LI-1400
(Lincoln, USA). Outside the greenhouse, a weather
automatic station Davis Weather-Link (Hayward,
USA) was installed containing sensors to measure
outdoor conditions air temperature (C),
relative humidity (C), solar radiation (W m-2)
and wind velocity (m s-1).
Figure 4 Calculated vs. measured values (a) of
the air temperature and (b) of the air relative
humidity.
(2)
(3)
(4)
(5)
Figure 5 Output of the InverSim model in a
personal computer.
CONCLUSIONS
The new model InverSim es able to calculate
inside air temperature and humidity of the a
greenhouse directly from the outside climatic
conditions. The comparison with measurements
shows that the present model allows a good
prediction of air temperature although the
relative humidity was less satisfactory due to
the fluctuations observed in some days between
the measured and predicted values.
Literature Cited
Boulard, T. and Baille, A. 1993. Agric. For.
Meteorol. 65145-157. Hanan, J.J.1997.Greenhouses
Advanced Technology for Protected Horticulture.
CRCPress 720 p. Jolliet, O. 1994. J Agric. Engng.
Res. 57 23-37. Kittas, C., Bartzanas, T. and
Jaffrin, A. 2003. Biosystems Engineering
85(1)87-94. van Henten, E.J. and Bontsema, J.
1996. Acta Hort. 406213-220.
Figure 1
Figure 2
Figure 1 and 2 Greenhouse used to validate the
InverSim model.