Simulation of the cooling effect of the night time natural ventilation: a 3D numerical application to the "Maison Ronde" of Mario Botta.

The present research applies the N3S 3D finite element CFD code to the air flow simulation on a well-known dwelling building located in South of Switzerland, the " Maison Ronde " of the architect Mario Botta. The summer night refreshing effect is examined when crossing ventilation due to the wind creates indoor air motion and for cooling walls and ceilings surfaces. To be realistic, the simulation takes simultaneously into account the three main aspects of the problem: - determining boundaries conditions. To avoid to set artificial or non realistic conditions at openings, the 3D mesh of the house is immersed in a numerical " wind tunnel ", at the frontier of which the wind profile is imposed. The incoming air flow is therefore the result of the outdoor aerodynamic effect of the building geometry and of the location of opened windows; - simulating the air flow with thermal conditions. The N3S code uses a thermal boundary layer at the walls that enable to compute the mixed convection effect induced by the temperature gradient between the wall and the surrounding air; - calculating the cooling effect of the air flow on the wall structure. A thermal model is integrated into the CFD code to model the transient behavior of the mass inertia walls. This paper presents firstly the technical aspects of the implementation of the cooling effect in a summer night ventilation situation and secondly its application to the "Maison Ronde" The simulation evaluates the transient evolution of the air flow, internal air and wall surface temperatures from realistic initial conditions corresponding to the beginning of the night. Obtained results are analyzed in relation to the architectural specificities of the house to explain its thermal behavior and appreciate the night cooling effect.