1. ´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@arnet.com.ar Universidad Nacional del Litoral Facultad de Ciencias Agrarias Departamento de Producción Vegetal 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). INTRODUCTION AIM Develop a model aimed to describe the dynamic behaviour of air temperature and humidity inside the greenhouse. Theory The greenhouse thermal behaviour during day time is described by means of a simplified energy balance equation: 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 ( Et, 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 ). (1) (2) (3) (4) (5) MATERIALS AND METHODS Figure 1 Figure 2 Figure 1 and 2: Greenhouse used to validate the ´InverSim´ model. RESULTS 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. 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. CONCLUSIONS Figure 4: Calculated vs. measured values (a) of the air temperature and (b) of the air relative humidity. Boulard, T. and Baille, A. 1993. Agric. For. Meteorol. 65:145-157. 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. 406:213-220. Literature Cited Figure 5: Output of the ´InverSim´ model in a personal computer.