Experimental study of five different VAV air terminal devices under variable heat gain conditions in simulated office and meeting rooms

Demand control of the air distribution systems is crucial to the satisfactory thermal environment under variable heat gain conditions in an energy efficient manner. In this study, the airflow patterns, ventilation performance and local thermal comfort have been experimentally investigated in mock-up meeting and office rooms with a variable air volume (VAV) system. The Active Diffuser, which had a constant inlet air velocity, was compared with some commonly used diffusers: Rectangular; Swirl-Radial; Swirl-Compact and Multi-Nozzle Diffusers. In the test, there were four different heat gain levels: high heat gain (46 W/m²) in a meeting room setting; high (46 W/m²), medium (24 W/m²) and low (11 W/m²) heat gain in an office room setting, respectively. The corresponding specific supply airflow rates in the high, medium and low heat gain cases were 4.3 L/s m², 2.1 L/s m², 1 L/s m², respectively. Visualized figures showed the effect of VAV on airflow patterns were quite different among different diffusers. The indexes including air velocity, ventilation effectiveness, effective draft temperature, draught rating and so on were therefore analysed. By using the Active Diffuser, the airflow distribution and most of these indexes were more uniform and more stable under the VAV. Although the Rectangular, Swirl-Compact, Swirl-Radial and Multi-Nozzle Diffusers might perform better in one or two cases regarding some indexes, their airflow patterns and performances of indexes were unstable under the VAV. Thus, the Active Diffuser was recommended for the VAV system for the application where heat gains vary significantly.