Experimental and numerical investigation of the tracer gas methodology in the case of a naturally cross-ventilated building

This paper presents the investigation of a naturally cross-ventilated building using both experimental and numerical methods with parameter being the incidence angle of the wind to the openings of the building. The experimental methodology calculates the air change rate based either on measurements of the inlet velocity profile, the outlet velocity profile or the descending rate of the tracer gas mass concentration using the decay method. The numerical investigation is based on the solution of the governing Reynolds averaged NaviereStokes equations in their full three dimensional expression, focusing on the time dependent character of the induced flow field. The numerical results are compared with corresponding experimental data for the three aforementioned experimental methodologies in the case of a full-scale building inside a wind tunnel. The numerical investigation reveals that for large incidence angle the flow is governed by an unsteady character regarding especially the regions close to the inlet and outlet windows. It is concluded that velocity measurements in the inlet window are of high accuracy when the flow in this region has a steady character, whilst the decay method is depicting the effective air change rate in a control volume and not the intended one. Finally, conclusions about the air change rate spatial distribution in the control volume of the building are provided as a function of the incidence angle, revealing that its accuracy as a method for measuring the intended aeration rate depends significantly on the mixing of gas within the control volume of the building.