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Comprehensive Guide to HVAC Duct Design for Residential Systems

This detailed guide covers the airflow patterns, static pressure distribution, fan selection, and duct design considerations for residential HVAC systems. Learn how to calculate pressure drops, select duct diameters, and optimize airflow efficiency. The process involves defining duct sizes, pressure drops, diffuser placement, flow rates calculation, and more. Explore various topics, including dynamic pressure, total pressure, fittings, local losses, and non-circular duct design. Dive into frictional losses, Moody's diagram, and local loss coefficients to enhance your understanding of duct design principles.

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Comprehensive Guide to HVAC Duct Design for Residential Systems

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Presentation Transcript

  1. Objectives • Airflow in Ducts • Fluid dynamic review • Duct Design

  2. Static pressure distribution Fan P+ Patm Patm P-

  3. Static pressure distribution in a residential HVAC system Supply 2 Supply 1

  4. For non-uniform duct diameter - apply Bernoulli equation Dynamic pressure 0 0 Fan We need fan for this Dynamic pressure ∆P total ∆P static Patm

  5. Relationship Between Static and Total Pressure

  6. Use of Static to Dynamic Pressure Conversion (and reverse)

  7. Duct design • Two objectives: • Define the size of duct sections • Define the pressure drop • Process: • Position and size diffusers • Layout desired pattern for supply • and return ducts • Calculate the flow rates for each duct • section • Select the duct diameter for each section • Measure the length for each section • Calculate the pressure loss for each section • Count the number, and define the type, of fittings and elbows • Calculate the pressure drop in fittings and • elbows • - Calculate the total pressure drop

  8. Local losses • Losses associated with • Changes in velocity • Obstructions • Bends • Fittings and transitions

  9. Fittings and elbows

  10. Pressure drop in duct v D L MOODY'S DIAGRAM Relative roughness e/D For unit length L=1

  11. Frictional Losses Shaded area

  12. Ductulator Same as the table in previous slide

  13. Non-circular Ducts • Also you can use hydraulic diameter

  14. Local Loss Coefficients ΔP local = CoPdynmaic

  15. Example Size the ducts and calculate pressure drop from - A to C - B to C A a c C b B Tabulated calculation: ……..

  16. Reading asignement • Chapter 18 • 18.1-18.4 (including 18.4)

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