Proposed Additions to Ventilation Duct-Design Procedures

摘要

The 'duct design' methods describe in Industrial Ventilation (IVM) are designed to aid practitioners in selecting appropriate duct 'sizes' (i.e., duct cross-sectional areas) and in selecting a fan for the system. With the exception of so-called 'branch entry coefficients,' the loss coefficients used in IVM are based on laboratory studies of individual components of the system (e.g., elbows, straight ducts, hood entries, etc.). The branch entry coefficients are based on Alden's estimates of plausible values. The duct design procedure in IVM is an attempt to model the behavior of the system created when the individual components are connected to each other. The 'total pressure method' presented in the American Society of Heating, Refrigerating, and Air conditioning Engineers (ASHRAE's) Fundamentals differs from the IVM method only in its model of junction fittings. The present work does not address the lack of field validation and it does not suggest fundamental changes to the IVM methods. Instead, we assume that the IVM methods are conceptually correct and reasonably accurate but could be modestly improved by incorporating the results of published studies on system modeling and by including the interactive models that will be discussed in succeeding sections. The former would have modest effects on most systems design to control particulates but would be moderately important for some plenum systems. The interactive modeling methods are modestly to moderately important when sizing ducts and selecting a fan but could be very useful when trying to understand the effects of modifying an installed system and for didactic demonstrations of system interactions with the fan and within branches.