New convection correlations for cooled ceiling panels in room with mixed and stratified airflow

Models for buildings' surface convective boundary conditions are important components Of building design and simulation programs. This is especially true for cooled ceiling (CC) panels, which extract major cooling loads from rooms. This paper introduces new convection correlations for rooms with CC panels, developed from laboratory measurements conducted in a full-scale experimental facility. The new convection correlations were developed for CC panels used with or without a ventilation system. When the ventilation system was used, the air was supplied through a high aspiration diffuser. High aspiration diffusers, recommended for use with CC systems, create a specific airflow pattern characterized by narrow and directional jets with a large entrainment of surrounding air. To account for the forced airflow and local buoyancy effects, new convection correlations for CC surfaces were developed as functions of temperature difference and normalized volume flow rate. i.e., the number of air changes per hour (ACH) in the room. Results show that the high aspiration diffuser, even though installed at the ceiling, produces enough air motion in the vicinity of the floor and vertical wall surfaces to affect the convective heat transfer at these surfaces as well. In fact, the effect of forced convection due to the presence of a high aspiration diffuser increases the total convection coefficient at CC surfaces by 4% to 17%.