ASHRAE ST-16-001

Abstract

Scope: Recent standards have defined a lower minimum air velocity in kitchen exhaust air ducts without compromising performance. Steel ducts are usually specified to a standard steel gage thickness capable of handling the extreme load conditions of high temperatures, possible corrosive conditions, and negative pressure levels within exhaust duct. This paper simulates a typical kitchen exhaust air duct performing under extreme temperature conditions and low air duct velocities. Lower exhaust air velocities should correspond to lower in-duct negative pressure values and, therefore, possibly a reduction in steel duct wall thickness. A computational fluid dynamics (CFD)/thermal stress analysis was carried out under the most extreme load conditions specified under recently issued standards. This analysis demonstrates that a lower-gage steel duct thickness is more than sufficient than what is specified in recent standards, and, therefore, a lower-gage steel thickness can be used.