INVESTIGATION OF NATURAL VENTILATION SYSTEM FOR A ONE STORY BUILDING

Abstract

Natural ventilation is an energy saving system for the building to ensure occupant’s physical comfort. Wind-driven natural (WDN) and buoyancy-driven natural (BDN) ventilation systems for a one story single room building were investigated. The basic flow field of WDN ventilation system of the scaled model was analyzed by flow visualization, Particle Image Velocimetry (PIV), and Computational Fluid Dynamics (CFD) techniques for three different cross ventilation cases based on the number and location of windows. The satisfactory comparisons between the results obtained from the computation and three experiments were aimed to provide an effective guideline to the numerous CFD users for the validation of future numerical approaches. A novel and intelligent numerical technique was proposed and applied to provide the insight of the mixing level quantification in WDN ventilation system. In each case of WDN ventilation system, the location of window in lateral and vertical directions, wind speed, and wind angle were varied to check the sensitivity of the ventilation performance to the changed design and conditions. The precision of the numerical methodology for BDN ventilation system was established by comparing the computational results with two reputed experimental results from the literature satisfactorily. The governing equations subjected to the corresponding boundary conditions were solved using the package software, ANSYS CFX 12.0 in all computations. The power and the inclination angle of the heating passage (HP) were varied to check the sensitivity of the ventilation performance to those factors. Three dimensionality, turbulence and mixing level of the indoor fluid were visualized in WDN ventilation systems. The overall performance was significantly affected by the particular design of the cross ventilation system. It was found that higher volumetric flow rate didn’t always ensure higher mixing level or vice versa. It also emphasized the necessity of three-dimensional (3D) approach to predict the indoor air movement correctly in studying natural ventilation system. A better location for the windows in each case was proposed. The ventilation purpose was served quite well even if the wind angle was changed in a moderate range from the original design. It was found that ventilation performance was significantly influenced by the lateral and the vertical positions of window and the wall porosity of the building. Furthermore, the velocity components, surface pressure, ventilation rate, ventilation time, mixing level, Air Change per Hour (ACH), ventilation efficiency etc. in each case were investigated and compared extensively with those in other cases of WDN ventilation system. The BDN ventilation system was found capable to serve the ventilation purpose whereas the building only contributed to the increment of the friction force. A proportional relation between the flow rate and the power was obtained. The ventilation rate was found the maximum when HP was attached to the building at 45°. The relations among Ra, Nu, Re and Pr obtained from the present BDN ventilation system were reported.