A Model for the Greenhouse Environment as Affected by the Mass and Energy Exchange of a Crop

Abstract

A mathematical model to compute hourly change of the greenhouse environment was designed. The system considered comprises the soil, crop, air and glass or vinyl cover. The feedback effect of the crop on the greenhouse environment is built in, and the temperature and humidity fields are simultaneously solved. Boundary conditions are the incident short-wave irradiance, the downward long-wave radiant flux density, the air temperature, the air humidity, the wind speed, all measured outside the greenhouse, and the water potential of soil in the greenhouse. The system is characterized by its scale, its properties regarding the heat transfer, the ventilation rate, and physiological characteristics of the crop about the water exchange. With these system parameters and boundary conditions, the model calculates not only the air temperature and humidity inside the greenhouse, but also the radiation balance, sensible and latent heat flux densities on the cover, the heat flux density through the cover, the latent and sensible heat exchange by ventilation, the radiation balance on the crop surface, the surface temperature of crop, and transpiration rate from the crop. The model was used to simulate the air temperature and humidity inside the greenhouse as affected by the ventilation rate. The results accorded qualitatively with experimental results so far reported.