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System Effects

AMCA International Technical Seminar 2009. System Effects. Presented by: Joe Brooks, AMCA International, Inc.

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System Effects

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  1. AMCA International Technical Seminar 2009 System Effects Presented by: Joe Brooks, AMCA International, Inc.

  2. The Air Movement and Control Association International (AMCA), has met the standards and requirements of the Registered Continuing Education Providers Program. Credit earned on completion of this program will be reported to the RCEPP. A certificate of completion will be issued to each participant. As such, it does not include content that may be deemed or construed to be an approval or endorsement by NCEES or RCEPP.

  3. Describe system resistance of components • Know how a fan interacts with the system • Define System Effect and System Effect Factor (SEF) • Know how to avoid system effect factors Learning Objectives

  4. Two Components of System Design • Calculate flow resistance losses for each component in the system • Select and position fan to avoid system effect loss • If loss cannot be avoided, estimate loss and select fan for higher pressure

  5. Ductwork Example System Effect Controlled by Inlet and Outlet Conditions System Resistance

  6. Causes of Non-Performing Systems • System resistance miscalculated. • Fan not properly selected. • Defective fan (or fan rating). • There is a system effect loss.

  7. Fan Manufacturer’s Responsibility • Provide accurate fan performance ratings. • Provide a fan built within tolerance so that it is capable of meeting its rating.

  8. What is System Effect? • A factor used to correct for system induced installation effects. • The difference in performance between a fan tested in the laboratory and one tested in a real installation.

  9. Inlet Connections ASHRAE Guidelines

  10. Outlet Connections ASHRAE Guidelines

  11. Outlet Connections ASHRAE Guidelines

  12. What is Missing? • Only guidelines to avoid losses. • No way to quantify losses.

  13. AMCA Publication 201-02 • The bible of system effects • Generated from ASHRAE funded research

  14. Credibility Gap • Are system effects just fudge factors that the fan manufacturers made up? • System effect video.

  15. Definition of System Effect • Fan ratings are established using AMCA 210 test codes that are close to ideal conditions. • Fans in actual systems are often less than ideal. • The difference in performance for the same fan tested in both conditions is the “System Effect”.

  16. Purpose of Discussion • Aimed primarily at the fan system designer There are two goals: • Avoid poor fan system configurations • When optimum conditions cannot be met, use the “system effect” factors to estimate any losses during system design.

  17. Why System Effect is Important • May have to accept deficient performance, or... • Speed up the fan (if possible) • May require more energy to meet performance • May exceed motor horsepower limit • Many cause excessive noise • Many cause excessive vibration

  18. Normal System Performance 1 Calculated duct system curve Fan curve Design volume

  19. Deficient Performance With System Effect System effect at actual flow volume • Operating point is at point 3 • Operating point is not on fan curve! 4 Calculated duct system with no allowance for system effect 1 3 Original fan curve Deficient volume Design volume

  20. Correcting For System Effect System effect at actual flow volume Actual duct system with system effect Calculated duct system with no allowance for system effect 2 System effect loss at design volume 4 1 New fan curve 3 Original fan curve Deficient volume Design volume

  21. With System Effects Added: • The fan will be selected for the higher pressure (no need to speed up). • The motor will be selected to include the anticipated loss.

  22. What are the Causes of the Losses? • Inlet losses are caused by: • Unequal loading of the fan blades (eccentric flow). • Improper fan blade attack angle. • Turbulence which disrupts the flow. • Outlet losses are caused by: • Loss of conversion of local high velocity into pressure.

  23. Inlet vs. Outlet Losses • Inlet induced losses tend to be higher than outlet losses. • Losses induced on the inlet can often exceed 20%. • Losses as high as 50% have been reported.

  24. Good Flow Conditions for a Fan: • Straight uniform flow directed only in the axial direction--on the fan inlet • For Ducted fans - a straight length of outlet ductwork

  25. AMCA Publication 210-07 • Defines standard methods of testing fans for rating purposes

  26. How are the Losses Quantified? • AMCA 201 publishes data for a variety of configurations • Most identify a “Loss Curve” which is based on the configuration and identified by a letter • Most also need the air velocity as a parameter.

  27. System Effect Curves Curve T Add 0.55 to Static Pressure 4000 FPM

  28. Outlet System Effects • In addition to the flow velocity, may need to know: • effective duct length • blast area

  29. System Effect Curves for Outlet Ducts - Axial Fans

  30. Fan Outlet Velocity Profile - Centrifugal

  31. System Effect Curves for Outlet Ducts - Centrifugal Fans

  32. Outlet Duct Elbows - Centrifugal Fans WORSE BAD

  33. S. E. Curves for Outlet Elbows on Centrif.

  34. S. E. Curves for Outlet Elbows - Axial

  35. S. E. Curves for Inlet Elbows - Axial

  36. Percentage of Unobstructed Inlet Area

  37. Fans and Plenum – Two Losses • Distance L / (Inlet Dia.) gives one loss • Loss factors given for 0.3 to 0.75 clearance • Note: Spacing for two fans is important • Keep inlet centerline on centerline of unit • No loss factors given

  38. Elbows Change the Velocity Profile Fan inlet here will create a system effect loss for any type of fan

  39. Right Angle Turns At Fan Inlet Inlet with special designed inlet box Inlet with rectangular inlet Duct (POOR) Inlet with 3-piece elbow All methods will induce some system effect loss. Some methods are better than others

  40. S y s t e m E f f e c t C u r v e s S y s t e m E f f e c t C u r v e s N o 2 D 5 D N o 2 D 5 D R / D R / D D u c t D u c t D u c t D u c t D u c t D u c t 0 . 5 O Q S 0 . 5 P - Q R - S T S y s t e m E f f e c t C u r v e s 0 . 7 5 Q R - S T - U 0 . 7 5 Q - R S U N o 2 D 5 D R / D 1 . 0 R S - T U - V 1 . 0 R S - T U - V D u c t D u c t D u c t 2 . 0 R - S T U - V 2 . 0 R - S T U - V - - N P R - S 3 . 0 S T - U V 3 . 0 S - T U V - D D D L e n g t h L e n g t h L e n g t h o f D u c t o f D u c t o f D u c t R R R System Effect - Round Inlet Ducts 2 piece mitered round section 4 or more piece mitered round section 3 piece mitered round section

  41. Forced Inlet Vortex (Inlet Spin or Swirl) Counter-Rotating Inlet Swirl Pre-Rotating Inlet Swirl

  42. Corrections for Inlet Spin

  43. Normalized Pressure-Volume Curve Note that this is similar to a variable system effect. A new curve is generated at each vane setting

  44. Pressure Drop Multipliers for Volume Control Dampers on a Fan Outlet

  45. Measured Inlet Sound Power Vaneaxial Fan System Effect Blade Pass - 135 Hz

  46. System Effect Factors are Real • When designing your fan/system, do everything possible to avoid a “system effect” for efficient use of energy • When conditions leading to system effect cannot be avoided, add the calculated loss to the fan pressure requirement at the system design stage.

  47. Thumb Rules • Minimum of 2-1/2 Duct Diameters on Outlet, • Minimum 3 to 5 Duct Diameters on Inlet, and • Avoid Inlet Swirl

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