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Airborne transmission of infectious respiratory diseases in indoor environments has drawn our attention for decades, and this issue is revitalized with the outbreak of severe acute respiratory syndrome (SARS). One of the concerns is that there may be multiple transmission routes across households in high-rise residential buildings, one of which is the natural ventilative airflow through open windows between flats, caused by buoyancy effects. Our early on-site measurement using tracer gases confirmed qualitatively and quantitatively that the re-entry of the exhaust-polluted air from the window of the lower floor into the adjacent upper floor is a fact. This study presents the modeling of this cascade effect using computational fluid dynamics (CFD) technique. It is found that the presence of the pollutants generated in the lower floor is generally lower in the immediate upper floor by two orders of magnitude, but the risk of infection calculated by the Wells-Riley equation is only around one order of magnitude lower. It is found that, with single-side openwindow conditions, wind blowing perpendicularly to the building may either reinforce or suppress the upward transport, depending on the wind speed. High-speed winds can restrain the convective transfer of heat and mass between flats, functioning like an air curtain. Despite the complexities of the air flow involved, it is clear that this transmission route should be taken into account in infection control. r

Building performance can be expressed by different indicators as primary energy use, environmental load and/or the indoor environmental quality and a building performance simulation can provide the decision maker with a quantitative measure of the extent to which an integrated design solution satisfies the design requirements and objectives. In the design of sustainable Buildings it is beneficial to identify the most important design parameters in order to develop more efficiently alternative design solutions or reach optimized design solutions. A sensitivity analysis makes it possible to identify the most important parameters in relation to building performance and to focus design and optimization of sustainable buildings on these fewer, but most important parameters. The sensitivity analyses will typically be performed at a reasonably early stage of the building design process, where it is still possible to influence the important parameters. The methodology is presented and an application example is given for design of an office building in Denmark.

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