A method of coupling CFD and energy balance simulations to study humidity control in unheated greenhouses

•A new method to couple CFD and EB simulations to improve greenhouse modelling is presented.•Ventilation rates and convective coefficients in a ventilated greenhouse using CFD have been obtained.•Ventilation strategies to improve the night-time climate in winter in unheated greenhouses are presented.

A coupling method is presented to study the night-time climate in greenhouses. The approach is based on two simulation methods: energy balance simulations (ES) and computational fluid dynamics (CFD). The coupled approach takes advantage of the strengths of each method and reduces their weaknesses. Two CFD parametric studies were carried out. The first one analysed the effects of different wind speeds and ventilator opening degrees on the ventilation rate. The second study assessed the effects of different sky temperatures and ventilator opening degrees on convective heat transfer coefficients. The CFD method was then coupled with the ES through the exchange of two variables: the CFD simulations provided the ventilation rates for the ES and the CFD method supplied the convective heat transfer coefficients used by for the ES. This coupling approach was applied to the study of night-time ventilation in an unheated, polyethylene-covered greenhouse where two important scenarios were addressed: clear-sky conditions and an overcast sky. Results from the two studies indicate that ventilation during the night-time in winter improves greenhouse climate; in the clear-sky case, relative humidity was reduced and the temperature was raised since ventilation reduced or eliminated thermal inversion, whereas in the covered-sky situation, ventilating reduced the humidity content, but the temperature dropped. As expected, the increases and drops in temperature and humidity also depended on external conditions. Minor opening angles produced the greatest changes in terms of greenhouse air temperature and relative humidity.