CoA numerical model was implemented to investigate the radiative and convective heat transfers in a closed glasshouse during the night. Simulations were carried out using a 2D turbulence closure model. Long-wave radiative fluxes were included by solving the radiative transfer equation. For the purpose of the study, a four-span greenhouse divided into two compartments was considered. Validation was undertaken on the basis of temperatures recorded on the walls and inside the greenhouse. The model showed its ability to reproduce the main characteristics of the climate inside the greenhouse. Several night climatic conditions from clear to cloudy sky were then analyzed for a 273 K outside air temperature in order to get an insight of the frost risks inside the building. Under clear conditions, the heat loss through the cover is not compensated by the heat flux from the ground and the temperature remains below 273 K in the whole greenhouse. Conversely, under cloudy conditions, the greenhouse gains energy and the inside air is almost 2 K warmer than the outside air. Due to the radiative emission of the glass, roofs are systematically 2 K cooler than the inside greenhouse air. The impact of the wind velocity on the greenhouse response was also investigated. The linear dependence of the convective heat transfer coefficient with respect to wind velocity is simulated with a slope comparable to values found in the literature.