Effect of gable roof with various roof pitches and obstacle heights on natural ventilation performance for an isolated building

Abstract

Numerical analysis based on CFD steady RANS equations was used to study the  airflow characteristics around and within an isolated gable roof building. Parameters that are the main study focus of this research include: streamlines of normalized velocity, pressure coefficient and ventilation rate. The effect of gable roof with four different roof pitches namely 15º, 25º, 35º & 45 were investigated against varying obstacle heights of 40, 50, 60 & 70 mm. From the simulation results, the streamlines show that larger roof pitch leads to increased velocity at the window and roof openings due to the external and internal pressure difference in the building. The corresponding increment in internal obstacle height on the other hand leads to gradual alteration of airflow direction in front of the obstacle, and also an increase of the pressure coefficient inside the building because of wind blocking effect. This pressure coefficient also sees a reduction in value at the windward and inside of the building with an increase in steepness of the roof pitch due to increasing internal velocity. Hence, airflow behavior and characteristics are clearly dependent on roof pitch and internal obstacle height which indicates a good agreement with the findings from the previous studies. Gable roof with a steeper roof pitch building coupled with lower internal obstacle height will therefore yield better ventilation rates.