A critical review on the performance and design of combined cooled ceiling and displacement ventilation systems

This paper reviews the studies and design of cooled ceiling and displacement ventilation (CC/DV) systems in buildings. If properly designed, the combined CC/DV systems can provide better indoor air quality and thermal comfort level compared to the widely used variable air volume (VAV) mixing systems. The cooling load removed by DV is a key design parameter. A low DV load has a positive effect on thermal comfort due to a small vertical temperature gradient, yet also has a negative effect on indoor air quality due to the increased mixing of room air. The impact of the room height on the temperature and contaminant concentration profiles is negligible in the occupied zone. The CC/DV systems are more effective in removing active contaminants (as indicated by CO2) than passive contaminants (e,g. VOCs). The condensation risk on the chilled ceiling panel is high because of the high humidity ratio in the region close to the panel. To prevent condensation on the panel, it is important to properly control the system for transient regimes, such as startup and shutdown periods, and to minimize infiltration of humid outdoor air. Whether a CC/DV system may or may not reduce energy consumption depends on the supply air temperature, outdoor airflow rate, and cooling load. Therefore, it is necessary to develop design guidelines for CC/DV systems for US buildings because the climate, building layout, and cooling load can be different from those studied elsewhere. (C) 2002 Elsevier Science B.V. All rights reserved.