Effect of outdoor wind on the hybrid natural ventilation performance of monitor roofs

Abstract

The monitor roof of a building has a raised structure running along the gable ridge, with its smaller roof parallel to the lower main roof. As a common building ventilation design, monitor roofs are expected to induce indoor airflow through thermal buoyancy and/or wind; however, studies on the design details and the induced natural ventilation performance are limited. In this study, how outdoor wind affects the efficiency of induced hybrid natural ventilation of monitor roofs was analyzed through computational fluid dynamics (CFD). Based on engineering practice and weather conditions, the Grashof number (Gr) was 2.11x1011-5.67x1011, and the Reynolds number (Re) was 2.5x105-1.7x106. The results indicated that for a larger monitor roof (width = 3 m, height = 1.2 m), the presence of outdoor wind combined with thermal buoyancy increased the ventilation rate to 1.5–3.5 times that found when only buoyancy was present. For a smaller monitor roof (width = 1.2 m, height = 0.3 m), Gr/Re2 = 0.45–3.2 was the transition range over which the presence of outdoor wind decreased the ventilation rate below that found when only buoyancy was present. Therefore, attention should be given to this disadvantage in ventilation design.

Keywords

• Natural ventilation
• Buoyant ventilation
• Monitor roof
• Roof
• CFD