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Multi-column attachment ventilation (M-CAV) is usually delivered to the occupied zone by floor-attached airflows in large spaces. However, after the floor-attached airflow converges, the original air distribution will change, which will have an important impact on the traditional air distribution design. In this paper, airflow convergence patterns and air distribution characteristics in the most common double-column and tri-column layouts are studied by experiments and computational fluid dynamics (CFD) simulations. A 1:3 scaled-down model was established for velocity experiments and flow field visualization, and the results were used to verify and optimize the CFD model. The results indicated a seagull-like convergence flow pattern under the symmetric double-column layout. Under the axisymmetric layout with different column spacings, the floor-attached airflow in the half-open air outlet mode exhibited full convergence with the merging point (point MP) and combined point (point CP), partial convergence with point MP, and non-convergence without point MP and point CP. Under the centrosymmetric layout, an M-shaped velocity distribution was formed, and no airflow converged. For equal-velocity conditions, the dimensionless convergence axial velocity distributions for different air supply velocities was approximately consistent. In the fully-open air outlet mode, the floor-attached airflow could be divided into the collision-dominated region, the combined collision and convergence-dominated region, and the convergence-dominated region based on the forms of airflow interaction. For unequal-velocity conditions, the high-velocity airflow restricted the diffusion of the low-velocity airflow. • Airflow convergence of multi-column attachment ventilation affects air distribution. • Characteristics of flow convergence are studied by visualization flow field and CFD. • Converging airflow forms a seagull-like flow pattern under the axisymmetric layout. • The half-open air outlet mode has no flow convergence in the centrosymmetric layout. • The calculation formulas of airflow diffusion width and axial velocity are given. [ABSTRACT FROM AUTHOR]

The conventional (square and circular) column attachment ventilation theory has been developed for many years. However, it is still unclear whether the cross-shaped column can be effectively applied to column attachment ventilation. This paper compared three column attachment ventilation models (i.e., circular, square and cross-shaped) by numerical simulation and experimental methods, the latter of which were mainly employed to verify and optimize the CFD model. The air distribution of these three ventilation models was studied in isothermal mode. Five cross-shaped column air supply outlet opening modes under cooling conditions were proposed, and their effects on the thermal environment distribution in the occupied zone were investigated. The intersection of the two attached airflows in the inner concave surface of the cross-shaped column changed the trends of the axial velocity variation. The attached airflow created a larger impinging zone near the internal corner of the cross-shaped column compared with the other surfaces. With the fixed air supply parameters, the kinetic energy loss at the column bottom under cross-shaped column attachment ventilation (CS-CAV) increased by approximately 60 % compared with that under square column attachment ventilation (S-CAV). CS-CAV is not only an effective ventilation method but can also meet the comfort needs of different occupied zones, providing a design basis for CS-CAV in buildings. • Cross-shaped column attachment ventilation is as effective as other ventilation. • Airflows interact at column internal corner, affecting indoor air distribution. • Cross-shaped column has five air supply modes because of multi-section slot outlet. • Cross-shaped column attachment ventilation creates different thermal environments. [ABSTRACT FROM AUTHOR]

Column attached ventilation (CAV) is a new form of air distribution based on pillars widely distributed in buildings. Due to thermal buoyancy in the room, the airflow mechanism and performance of CAV is uncertain when it is applied for winter heating, especially in buildings with large space. In this study, a simplified three-dimensional model was established based on a shopping mall. A Computational Fluid Dynamics (CFD) method was employed to simulate the airflow in the room. Archimedes number (Ar) was used to study air distribution and ventilation performance. Results indicated that CAV could be used for room heating, and inertia force was the main driving force of the airflow. In the occupied zone, air velocity and temperature could be controlled by supply air velocity and temperature. Ar was related to air distribution and ventilation effect. In selected cases, Ar less than 2.241 × 10−3 was the prerequisite for effective air distribution. Heat removal effectiveness was linearly related to Ar, and it increased by about 0.01 when Ar reduced by 0.1. CAV saved more energy than mixing ventilation to achieve the same parameters of the occupied zone. These results provide a theoretical basis for the application of CAV in winter conditions. • Column attached ventilation (CAV) can be used for room heating. • Archimedes number can determine whether CAV forms effective air distribution. • In the occupied zone, the inertial force dominates the CAV air distribution. • Average room temperature increases linearly with increasing supply air temperature. • CAV has a higher heat and CO 2 removal effectiveness than mixing ventilation. [ABSTRACT FROM AUTHOR]