A physical model for water balance in a semi-closed greenhouse
The dynamic water balance in a greenhouse can be a complicated process consisting of submodels, most of which require the estimation of several parameters. A general water mass balance model represents a big research step for the semi-closed greenhouse, located at the Institute for Agriculture and Horticulture Sciences at Humboldt University of Berlin. This particular work focuses on two cases: a completely closed greenhouse where only the processes of condensation and transpiration are taking place. The second model includes transpiration, condensation and also natural ventilation is allowed for short periods of time. Both models were calibrated to find the optimal parameter values to improve their predictions. A sensitivity analysis was performed only for the second model, because the number of parameters was bigger. The purpose of both models was to simulate the air humidity behavior under closed and semi-closed conditions, and to find the most important parameters which affect humidity. The models were implemented using Simulink in Matlab. In the first model four parameters were calibrated: the two parameters that changed the most were the boundary layer resistance and the radiation extinction coefficient. The sensitivity analysis for the second model revealed that the latent heat of vaporization and radiation extinction coefficients were the most sensitive parameters. Seven parameters were calibrated being the aerodynamic resistance and the dimensions of the windows the parameters with more changes after calibration. The Mean Absolute Error and the correlation coefficient obtained in both models, indicates that absolute and relative humidity can be simulated with acceptable accuracy, when the semi-closed greenhouse is completely closed or when natural ventilation is allowed.
Salazar, R., López-Cruz, I.L., Mauricio, A.M., Schmidt, U. and Miranda, L. 2017. A physical model for water balance in a semi-closed greenhouse. Acta Hort. (ISHS) 1170:183-192
transpiration, condensation, ventilation, Simulink