ASHRAE ST-16-005

Abstract

Scope: The purpose of this research project is to provide a simple yet accurate procedure for calculating the minimum distance required between the outlet of an exhaust system and the outdoor air intake to a ventilation system to avoid reentrainment of exhaust gases. The new procedure addresses the technical deficiencies in the simplified equations and tables that are currently in ANSI/ASHRAE Standard 62.1-2016, Ventilation for Acceptable Indoor Air Quality (ASHRAE 2016a), and model building codes. This new procedure makes use of the knowledge provided in Chapter45of the2015ASHRAEHandbook—HVACApplications (ASHRAE 2015), and was tested against various physical modeling and full-scale studies The study demonstrated that thenewmethod is more accurate than the existing Standard 62.1 equation, which underpredicts and overpredicts observed dilution more frequently than the new method. In addition, the new method accounts for the following additional important variables: stack height, wind speed, and “hidden” intake. The new method also has theoretically justified procedures for addressing heated exhaust, louvered exhaust, capped heated exhaust, and horizontal exhaust that is pointed away from the intake