Pseudo bond graph model of coupled heat and mass transfers in a plastic tunnel greenhouse

Abstract

In greenhouses, models built are classified into two kinds; heterogeneous approaches based on computational fluid dynamics (CFD) codes and homogeneous one based on heat and mass balance equations. Bond graph modelling was not seriously introduced in greenhouse modelling in spite of the concordance of the energetic based approach of bond graphs with the nature of the greenhouse plant. In this research work, a pseudo bond graph model of a greenhouse was elaborated to simulate temperature and relative humidity inside. The model proposed is an energetic lumped approach which describes coupled heat and mass transfers in a plastic tunnel greenhouse. This model includes convection, evaporation/condensation phenomena, air change flow and soil heat and mass transfer. Multiport (3 ports) bond graph elements are introduced to describe the state of the two elements (dry air and water vapor) fluid. New bond graph schemes are used to characterize the coupling effect between heat and mass transfer, and for modelling free evaporation/condensation mechanism. Big leaf assumption was used to model the canopy. New boundary layer elements are added in the model, these elements allow a separation of the different phenomena inside greenhouse and thus a simplification of the modelling task. The practical results obtained from an experimental tunnel greenhouse are used here as validation elements for the greenhouse bond graph model. A good correlation is observed between measured and predicted samples.