Energy and Buildings 76 (2014) 640–653 Contents lists available at ScienceDirect Energy and Buildings j ourna l ho me pa g e: www.elsevier.com/locate/enbuild Air change rates driven by the flow around and through a building storey with fully open or tilted windows: An experimental and numerical study Renate Teppner a,∗ , Bernd Langensteiner b , Walter Meile b , Günter Brenn b , Sybill Kerschbaumer c a AIT Austrian Institute of Technology GmbH, Energy Department, 1210 Vienna, Austria b Institute of Fluid Mechanics and Heat Transfer, Graz University of Technology, 8010 Graz, Austria c Dr. Pfeiler GmbH, 8010 Graz, Austria a r t i c l e i n f o Article history: Received 19 September 2013 Received in revised form 5 February 2014 Accepted 4 March 2014 Available online 13 March 2014 Keywords: Natural ventilation Air change rate Wind tunnel experiments Computational fluid dynamics Residential buildings a b s t r a c t Air change rates (ACH) through open and tilted windows in rooms of residential buildings driven by atmo- spheric 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. © 2014 Elsevier B.V. All rights reserved. 1. Introduction In the planning process of a building, the heating and cooling concepts are developed, and both have the ventilation concept as an integrated part. Mechanical, natural and even hybrid ways of venti- lation are nowadays in use. Natural ventilation of buildings, relying on wind-induced pressure or on differences in temperature, is the most common form of ventilation. The air is exchanged through doors, open or tilted windows. For layout purposes it is important to estimate the magnitude of the air change rates (ACH) correctly. Ventilation through tilted windows is sparsely represented in the literature to date. The amount of air exchange strongly depends on the wind direc- tion as well as on the position and size of the openings of the ∗ Corresponding author. Tel.: +43 505506411; fax: +43 505506613. E-mail address: renate.teppner@ait.ac.at (R. Teppner). building envelope and, in presence of different temperatures inside and outside the building, on thermal buoyancy. The methods for studying natural ventilation are either full scale experiments in real conditions [1–4], wind tunnel experiments in full or model scale [5–8], or computational fluid dynamics (CFD) simulations. CFD results are compared with analytical results or data from wind tunnel measurements [2,5–7,9–13]. Furthermore, network mod- els [14,15] which can be used to predict wind-driven ACH quite accurately, are compared with CFD models in the absence of exper- imental data [16]. The existing literature reports on various experimental and numerical studies aimed to estimate air flow rates through open- ings and the resulting indoor air quality. Allocca et al. [2] and Larsen and Heiselberg [3] investigated both wind-driven and thermally induced air exchange. In their studies, a consistent trend to pre- dict the interaction of the two mechanisms was not found. Schulze and Eicker [14] investigated three cases under mixed conditions applying local weather data. For a single-sided situation they found http://dx.doi.org/10.1016/j.enbuild.2014.03.004 0378-7788/© 2014 Elsevier B.V. All rights reserved.