Modeling and characterizing bi-directional airflow in natural ventilation

Abstract

Bi-directional airflow in natural ventilation is an essential but not-well-understood scenario due to the complexity of airflow patterns as well as the strong coupling effect between temperature and ventilation. Neglecting bi-directional natural ventilation will result in problematic solutions and inaccuracy in estimation of ventilation performance. This work is focused on filling the knowledge gap by understanding the bi-directional airflow using computational fluid dynamics (CFD). Two important scenarios are simulated and analyzed: 1. Two-zone model with pure buoyancy forces, 2. Multi-zone model with combined wind and buoyancy forces. In the 1st model, a new concept of "local discharge coefficient" is proposed for its consistency under different boundary conditions. The influence of radiative heat transfer on simulation accuracy and ventilation performance is also investigated. In the 2nd model, the transient behaviors of airflow and the dynamics of wind and buoyant forces are analyzed and characterized. A new physical model is proposed based on simplified assumptions and nondimensionalization. This model is able to predicting the transient behavior of multi-zonal ventilation that involves bidirectional airflow patterns. The result of this study is to be integrated in CoolVent, the software designed by Building Technology Lab.