scope:

ABSTRACT

Incomplete mixing of outdoor and return airstreams in HVAC mixing boxes can lead to coil freezing in extremely cold weather, nonuniform temperature distribution issues, and control issues and other difficulties. In this study, computational fluid dynamics (CFD) was used to see how it might contribute to a better understanding of mixing boxes including mixing, dampers, and controls. Three geometries were considered with outdoor airflow entering from the side, back, and top of the mixing box, respectively. Many simulations suggested that good mixing is not obtained under a wide variety of conditions, dampers interact with each other, and good control of outdoor airflow requires an independent means of measurement and control with feedback.