Air change rates driven by the flow around and through a building storey with fully open or tilted windows: An experimental and numerical study

Air change rates (ACH) through open and tilted windows in rooms of residential buildings driven by atmospheric motions are investigated to evaluate natural ventilation concepts. Model experiments in wind tunnels, numerical flow simulations (CFD) and thermal building simulations are used. Pressure profiles are measured on the facade of a building model for selected wind directions and velocities. A separated sample storey and a sample single room in larger scales were used to measure air transport through window openings under the influence of the external pressure distribution. The ACH was obtained by velocity measurements in the window cross sections and by tracer gas measurements using the decay method.ACH from CFD computations of the wind tunnel environment agreed well with the experimental values. Therefore the numerical simulations were extended to real dimensions. The dependency of the ACH on the position in the external flow field and a scaling law for the ACH are presented. The wind-driven ACH obtained are much larger than the temperature-driven values prescribed in the Austrian standard Ö-NORM B 8110-3 on the prevention of high room temperatures during summer. A comparison of the impact of temperature-driven with wind-driven ACH, i.e. natural ventilation concepts, in thermal building simulations is presented.