A numerical investigation into natural ventilation of double skin façades and the improvement of energy efficiency in high rise buildings

Abstract

Buildings consume a large amount of energy, around 40% of global energy use. Under keeping comfortable environments for building occupants, reduction of buildings’ energy use is significant and also challenging. Passive techniques, such as natural ventilation, are promoted in certain climates to provide low energy cooling and ventilation. However, controlling natural ventilation in an effective manner to maintain occupant comfort can be a difficult task, particularly during warm periods.

One of the passive techniques is carefully designing building façade, e.g., ‘double-skin faҫade’, one of the best options in managing the interaction between the outdoor and internal spaces. Double-skin façade (DSF) building is one of the energy conservation opportunities available through recent intelligent buildings. Not only does the façade constitute the architectural aesthetics of the building, but it is also of great importance due to its impact on energy performance and interior function. Therefore, the development of innovative façade technology continues to be one of the most active research areas for the built environment. In this work, an investigation into the optimal application of a double-skin façade (DSF) for high-rise buildings is presented using computational fluid dynamics (CFD) approaches.

The work firstly reviewed state-of-the-art research, technologies and applications for double-skin façades. Based on the review, the author then proposed some new and innovative forms of double-skin faҫade which are particularly
applicable to high-rise buildings. These façades offer natural ventilations for tall office buildings. The forces driving the ventilations, i.e., buoyancies, are produced from the solar energy. As CFD is applied, the effects of the wind and buoyancy are then investigated separately or in combination.

The overall objectives of the investigations are to determine whether the magnitude of airflow rates and the desired flow pattern through openings can be achieved over a range of specified conditions. Potential conditions where the design goals may not be ensured are identified. It is supposed that a seasonal control could be developed to provide the optimum desired flow pattern, sufficient flow rates for ventilated cooling and uniform airflow rates across floors. Segmented and non-segmented DSF cavity patterns with ventilated double façades are adopted as the main building configurations for coping with the potential magnitude of wind at high levels. The ducts between cavities are designed to control the natural ventilations in tall office buildings. Steady state condition approaches are adopted for investigating these cases. The results show that segmentation has tends to create relatively uniform air pressure, airflow and temperature at various elevations within the building, and therefore has the best performance.

In order to quantitatively assess the performance of the proposed double-skin faҫades, various CFD models were developed. These models are involved in turbulence calculations with kappa-epsilon model heat transfer. Various validations of the CFD models show that the models are able to produce precise
results. Ultimately, the CFD, CFX5 codes were applied to estimate and investigate the performance of the proposed DSFs and produce the optimal application of double-skin façades for high-rise buildings.