A
APPENDIX A
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Example Design Requirements:
Design Friction Rate – 0.1 IWC/100 ’ 170 CFM
Duct selection is then based on the intersection of the green lines in the graph above. The intersection occurs between 7” and 8” duct, approximately a 7.5” duct. The size is rounded upward to meet the final selection of 8”.
NOTE: When using a friction chart or duct slide rule ensure that you are using the manufacturers provided slide rule. Slight variations in design and manufacturing can cause the friction numbers to vary between manufactures. If no data is available, use the generic flexible duct friction loss chart in ACCA Manual D. NEVER use a sheet metal friction chart or duct slide rule when sizing a duct. The walls of sheet metal are smoother than flexible ducting which means the friction amounts will differ significantly. Using a sheet metal friction chart will result in an incorrectly sized HVAC duct system.
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