Duct sizing chart - pressure loss

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SUMMARY

The discussion centers on a duct sizing chart that highlights pressure loss, particularly noting a change in the upper pressure loss limit to 0.7 Pa/m for ducts larger than Ø800. This change is attributed to velocity issues rather than pressure losses. Participants mention using a duct sizing calculator, specifically a rotary slide rule, which lacks similar markings. The chart can be accessed at a provided link, which contains relevant information for understanding duct design limits.

PREREQUISITES
  • Understanding of duct sizing principles
  • Familiarity with pressure loss calculations in HVAC systems
  • Knowledge of airflow velocity and its impact on duct design
  • Experience with duct sizing calculators, such as rotary slide rules
NEXT STEPS
  • Research the impact of airflow velocity on duct pressure loss
  • Explore advanced duct design techniques for systems exceeding Ø800
  • Learn about the economics of duct material selection
  • Investigate noise reduction strategies in duct systems
USEFUL FOR

HVAC engineers, duct design specialists, and anyone involved in optimizing ventilation systems will benefit from this discussion.

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I found this sizing chart for ventilation ducts. Notice the gray area for what I suppose is the accepted pressure loss area. What I wonder is why it changes as the sizes pass Ø800. From here on the upper pressure loss limit goes down to 0,7 Pa/m. Is this because of velocity issues or something else?
 

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That's something I should probably know, but I don't. It could be an issue of duct strength, economics, noise. I'm really not sure. I use a duct sizing calculator (rotary slide rule, basically) which has no similar markings. where did you get it?
 
I'm pretty sure it's a limit on velocity, and not on pressure losses. 200,000 l/s of gas rocketing through a pipe at 40 m/s is not within typical design limits.
 

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