CFD simulations of the night-time condensation inside a closed glasshouse: Sensitivity analysis to outside external conditions, heating and glass properties

Abstract

Humidity and temperature are key factors in greenhouse climate management since they impact crop growth. For example, under high humidity and low temperatures, condensation may occur and lead to crop damage. In order to assess the condensation mechanism inside a closed greenhouse during the night, a closed monospan 100-m2 Venlo glasshouse was considered and 2D transient CFD simulations were conducted with particular attention paid to condensation and crop transpiration since this combination had rarely been considered before in CFD models. Radiative exchanges were included through a specific submodel and a user-defined function was activated to take account of both heat and mass transfers induced by crop transpiration and by condensation along the greenhouse walls. The aim was, to validate the CFD model by comparing simulations with experimental results and to analyse in detail the influence of external conditions, heating and glass properties on the greenhouse climate. Five parameters were successively tested: external temperature, wind velocity, sky temperature, emissivity of the glass and ground heat flux. Results revealed the ability of the model to predict both the air and wall temperatures of the greenhouse. The root-mean-square difference between the simulations and measurements was <1 K for all temperatures and <11% for relative humidity. Condensation appears to have a strong impact on the resulting relative air humidity inside the greenhouse. A sensitivity analysis showed that low external or sky temperatures may increase condensation because they lead to a considerable decrease in wall temperature.