A Comparative Analysis of Displacement Ventilation with the Overhead Mixing Systems
ASHRAE Winter Conference, Dallas, TX, 2013
Computational Fluid Dynamics (CFD) models are developed to compare the performance of displacement ventilation with the overhead mixing ventilations system for the same space with identical heating and cooling loads. As expected, during the summer cooling conditions, the displacement ventilation system creates stratified temperature distribution with cold air near the floor and hot air near the ceiling of a two-story lobby. In contrast the overhead system with side wall linear diffusers creates well mixed uniform temperature. Both the systems can provide similar thermal comfort for the occupants. Due to narrow width of the lobby the occupants sitting in the vicinity of the displacement diffusers may experience draft at their feet level. During the winter heating conditions the supply airflow rates for both systems were reduced to meet only the ventilation requirements whereas the finned-tube heat exchangers were placed near the perimeter of the lobby to meet the heating needs of the space. The CFD simulation results indicate that when equipped with separate heating systems both displacement and overhead systems can provide well mixed uniform temperature conditions without stratification. During the winter heating conditions also both systems can provide acceptable and comparable thermal comforts for occupants.