The Feasibility of Natural Ventilation in Chicago’s Tall Office Buildings Using Double-skin Façades

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Kim, Yohan
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Thirty-one tall buildings (i.e., buildings of or taller than 200 m) have been erected to date in Chicago; 51% accounting for office function, according to the Council on Tall Buildings and Urban Habitat (CTBUH). Their energy- efficiency and healthy environment have become important concerns, given the current environmental challenges and health considerations. Many strategies in improving the properties of windows and building systems have been adopted to save energy and improve the working environment in tall office buildings in Chicago. However, only a few passive design techniques for natural ventilation have been employed. Double-skin façade (DSF) systems can provide an opportunity to apply natural ventilation strategies to tall office buildings, as they can mitigate the high wind speed and pressure through the additional skin and regulate the vertical stack flows through the segmentation. This study will investigate the feasibility of natural ventilation in Chicago’s tall office buildings using DSFs. Computational fluid dynamics (CFD) simulations will be conducted to assess the performance of parametric DSF configurations, including opening size and location, cavity depth, and cavity segmentation based on indoor air velocity, indoor operative temperature, and air change rate calculated under specific climatic conditions in the simulations. These results, as related to thermal comfort and indoor airflow behavior, are important criteria for the ventilation requirements established in the ASHRAE standard. Wind tunnel tests will be conducted to validate the CFD simulation results. The DSF configuration is a key determinant of the distributions of air velocity and indoor temperature on each floor, and the proportion of driving forces between wind and stack effects. In order to assess the feasibility of natural ventilation in tall office buildings, which rely highly on mechanical ventilation, the maximum number of natural ventilation hours throughout the year in Chicago will be predicted based on the analysis of the simulation results and the weather data. The proper DSF configurations with quantified natural ventilation will lead to a better understanding of how DSFs should be designed for tall office buildings and provide a performance-based design guideline for the early design stage in which iterative and rapid design decisions are made.
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