A numerical study on the effect of column layout on air distribution and performance of column attachment ventilation

Based on the structural characteristics of existing buildings and the disadvantages of current mixed ventilation mode in the application to large space buildings, an original column attachment ventilation (CAV) has been proposed. In this study, the experiment utilized a room space with four columns uniformly distributed in the space to visualize the movement of attached airflow along the cylinder surface and the floor, the numerical technique was employed to study the effects of the column layout (i.e., uniform, centralized, dispersed, and crossed distribution) on the air distribution of CAV mode in a standard four-column full scale model of a shopping mall. Seven indices, including airflow pattern, air diffusion performance index (ADPI), air temperature distribution, heat removal effectiveness, draught rate (DR), predicted mean vote (PMV), and carbon dioxide (CO2) concentration, were used to assess the ventilation performance. In the CAV mode with a uniform column layout scheme, the experimental results indicated that the air supply flows downward along the wall surface, forming a secondary attachment with the ground and spreading along the floor in a fan radiation flow mode. Further, an "air lake"-like speed and temperature distribution similar to displacement ventilation (DV) was formed in the occupied zone. In all simulation cases, it was found that the average air velocity was less than 0.25 m/s in occupied zone, the effectiveness for heat removal was more significant than 1.0, DR value was less than 20%, the PMV level can also satisfy most people. The average CO(2)concentration was around 470 ppm in the occupied breathing zone. These results indicated that the CAV mode could be an efficient air distribution method. They demonstrated the technical feasibility of applying the CAV in the space under different column layout schemes.