In-situ modelisation of a greenhouse climate including sensible heat, water vapour and CO2 balances

Abstract

While thermal structures such as greenhouses are complex to model under transient conditions because of coupled heat and mass (H2O and CO2) exchanges between their different parts, systems theory allows a simple analysis of the input/output behaviour of the model. In particular, parameters of the reduced dynamic models can be derived from in-situ measurements on these systems. This paper describes an application of the systems approach to a greenhouse climate model which incorporates CO2 balance, crop transpiration and photosynthesis and the effects of heating, CO2 enrichment, natural ventilation and evaporative cooling. In a first stage, system parameters such as the equivalent thermal mass, the wind dependent coefficient of natural ventilation and the various heat exchange coefficients were identified in situ from sequences of input-output data concerning the heat and water vapour balance, recorded over the crop production period from December to July. Good agreement between measured and computed values of air temperature, air humidity was observed. In a second stage, we have considered simultaneously the sensible heat, water vapour and CO2 exchanges and tested the model against experimental data measured using a commercial greenhouse climate control computer. The identified values of the physical and physiological parameters are close the theoretical values and the accuracy of temperature, humidity and CO2 content is rather good. © Owned by the authors, published by EDP Sciences, 2013.