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A new duct sizing calculator from ASHRAE and the Air Distribution Institute (ADI) enables designers of air distribution systems in HVAC to obtain greater precision in duct size, especially flexible ducts in various amounts of compression, based on research results.
The Duct Size Calculator is a quick reference tool for approximating duct sizes and equivalent sheet metal vs. flexible duct sizes. The calculator uses information from ASHRAE's Research Project 1333, "HVAC Duct Efficiency Measures," and was developed with financial support from ASHRAE and ADI. The ASHRAE 5.2 Technical Committee, Design Conduit, sponsored the project.
"While the calculator resembles a wheel similar to those used during slide rule days, it incorporates three new fields for sizing equivalent ducts," said Chris Van Rite, developer of the calculator. "These new fields help demonstrate significant loss of airflow due to improper installation of flexible ducts."
The calculator includes fields for compression of 4, 15 and 30 percent in flexible ducts. Van Rite points out that the calculations used to create these size references are based on straight-line compression performed in the lab on a flat surface. Flexible ducts installed in the field with curves, kinks and excessive lengths will have additional strength, resulting in decreased airflow.
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