LV-22-005 -- The Use of CFD to Understand Mixing, Controls, and Dampers in Air-Handling Units

Incomplete mixing of outdoor and return airstreams inHVAC mixing boxes can lead to coil freezing in extremely coldweather, nonuniform temperature distribution issues, andcontrol issues and other difficulties. In this study, computationalfluid dynamics (CFD) was used to see how it mightcontribute to a better understanding of mixing boxes includingmixing, dampers, and controls. Three geometries were consideredwith outdoor airflow entering from the side, back, and topof the mixing box, respectively. Many simulations suggestedthat good mixing is not obtained under a wide variety of conditions,dampers interact with each other, and good control ofoutdoor airflow requires an independent means of measurementand control with feedback.