Minimizing Energy Consumption, Eliminating Excessive Noise With Duct Design Best Practices

From Insights Newsletter, July 2021

Ducts in air-distribution systems are designed to transport a given volume of air as efficiently and quietly as possible to minimize energy consumption and eliminate excessive noise. The duct design process requires engineers to consider multiple factors, such as duct system layout, fitting selection, leakage, acoustics and equipment selection.

The recently released Duct Systems Design Guide, written by Herman Behls, P.E., Fellow/Life Member ASHRAE, is a resource to guide HVAC engineers and designers seeking to develop more energy-efficient, accurate, user-friendly and cost-efficient HVAC duct systems. The design guide gives engineers the tools to design properly sized duct systems to minimize fan energy consumption, system-generated noise and the installed cost of ductwork.

“This guide describes procedures useful for entry-level engineers and designers who are first learning about duct design fundamentals. The guide will also be a valuable tool for more experienced engineers and design professionals wishing to refresh their design knowledge,” said ASHRAE Technical Committee 5.2, Duct Design.

The design guide is meant to help engineers design energy-efficient HVAC systems that deliver the proper quantity of air to specific areas of a building or zones while minimizing first costs and operating costs in addition to providing a comprehensive design and a high-quality project with adequate funding and minimum construction disputes to the owner.

Material Selection Guidance

One section of the design guide speaks to a common source of anxiety for engineers. “Engineering specifications are notorious for referencing every manual and handbook that's out there,” said Larry Smith, P.E., Member ASHRAE, chair of ASHRAE’s Technical Activities Committee.

The chapter in the design guide dedicated to material selection and specifications points HVAC designers to credible resources and specifications to consider when conflicting code requirements crop up, said Smith, who is TC 5.2’s duct leaking and sealants subcommittee chair. The chapter points duct designers to the places to find information on design guidance material selections, and what codes they should take into consideration during the design process.

This chapter consolidates material selection and consideration guidance into one place, said Smith. “This information isn’t compiled anywhere else. It doesn't really exist in the Handbook, and it can’t readily be found in any other reference,” he said.

The Design Guide’s Origin Story

The work on this recently released design guide began more than 20 years. In 1998, TC 5.2 began talking about creating a duct design manual that did not exist but was needed. Originally conceived as an ASHRAE research project, TC 5.2 took control of the editorial process and accepted the task of authoring the guide after it became apparent that writing a duct design guide suitable for these disparate audiences was exceptionally challenging.

Behls, a former chair of TC 5.2, volunteered to complete writing the guide. Unfortunately, Behls died in 2017, and Pat Brooks, P.E., Life Member ASHRAE, TC 5.2’s ASHRAE Learning Institute Coordinator; Steve Idem, Ph.D., Member ASHRAE; and Smith saw the project through to completion. Behls is credited with writing the design guide.