14 Stall Parallel Operation [Kompatibilittsmodus] Effect Axial Fans (none stall-free) Stall...

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Transcript of 14 Stall Parallel Operation [Kompatibilittsmodus] Effect Axial Fans (none stall-free) Stall...

  • Stall & Parallel Operation

    Witt&Sohn AG Oct-14

  • Stall & Parallel Operation

    1. Definition of Stall

    CONTENT

    1. Definition of Stall

    2. Requirements for Parallel Operation

    3. Operation of Parallel Fans

    4. Stall-free Fans & VSD

    Witt&Sohn AG Oct-142

  • Stall means: status of non-uniform flows, two air flows at one pressure value,

    Definition of Stall, Stall Definition

    Typical Axial Fan Curve, Single Operation:

    Stall area:forbidden for operation. Operation range

    Witt&Sohn AG Oct-143

  • Stall means, status of non-uniform flow, two air flows at one pressure value,

    Definition of Stall, Stall Definition

    Typical Axial Fan Curve (2 Fans Parallel Operation)

    Operation range

    Typical Axial Fan Curve (2 Fans Parallel Operation)

    Stall area:forbidden for operation.

    Witt&Sohn AG Oct-144

  • Typical Axial Fan Curve (4 Fans Parallel Operation)

    Stall means, status of non-uniform flow, two air flows at one pressure value,

    Definition of Stall

    Typical Axial Fan Curve (4 Fans Parallel Operation)

    Operation range

    The more fans run in parallel the larger the stall area the smaller the operation rangeThe STALL zone for axial fans in parallel often is much larger than expected !

    Stall area:forbidden for operation.

    Witt&Sohn AG Oct-145

  • Definition of Stall

    Disturbance causes the air flow to separate from one or more of to separate from one or more of the blades.

    This blocks the air flow through the corresponding blade cell.

    Witt&Sohn AG Oct-146

  • Curve of one fan

    Summary curve of two fans

    Definition of Stall

    Max. allowed system resistance without any saftey margin

    Several fan suppliers do not show or do not know in detail the STALL area of their fan curves

    Stall area of pd-line

    Witt&Sohn AG Oct-147

    Always ask for fan curves starting at 0m/s!

    Stall area of one fan Stall area of

    two fans (summary curve)

    pd-line

  • Possible Consequences:- rupture of air stream lines at blade edge - high vibrations with low amplitude at blade

    Definition of Stall

    - high vibrations with low amplitude at blade- damage of bearings- fatigue break of impeller

    Witt&Sohn AG Oct-148

  • Reasons: Turbulent inlet or outlet flow at the fan System resistance too high because of unexpected aerodynamic

    behaviour (wrong system design)

    Definition of Stall

    behaviour (wrong system design) Short-term pressure pulses

    (due to Piston Effect of by-passing trains)

    Witt&Sohn AG Oct-149

  • Piston Effect

    Axial Fans(none stall-free)

    Piston effect

    Stall operation likely for none stall-free fans due to piston effect of by-passing trains (Metro/Railway application)

    Witt&Sohn AG Oct-1410

    stall !

    Piston effect

    - 610Pa

    +610Pa

  • Piston Effect

    Axial Fans(none stall-free)

    Stall operation likely for none stall-free fans due to piston effect of by-passing trains (Metro/Railway application)

    stall !

    Piston effect

    +610Pa - 610Pa

    Witt&Sohn AG Oct-1411

    stall !+610Pa - 610Pa

  • Detection of stall

    Stall detection probe by WITT&SOHNWITT&SOHN

    Stall detection is done by a Petermann probein combination with a pressure sensor

    - + Probe located radially in the area of blade tip

    During normal (stable) operation the probedetects a negative or no pressuredifference.

    Stall is detected if the pressure difference exceeds a predefined value

    Witt&Sohn AG Oct-1412

    NOTE: A stall detection probe does not eliminatethe stall area of the fan. It only detectsthat the fan is not running in a stable area. Operation of fans in such conditions shall be avoided!

  • Stall & Parallel Operation

    1. Definition of Stall

    CONTENT

    1. Definition of Stall

    2. Requirements for Parallel Operation

    3. Operation of Parallel Fans

    4. Stall-free Fans & VSD

    Witt&Sohn AG Oct-1413

    4. Stall-free Fans & VSD

  • For System: High volume flow

    (Qdesign > Qsingle fan)

    Requirements for Parallel Operation

    (Qdesign > Qsingle fan) Moderate pressure drop Restricted space Heat resistance Reversibility (up to 100%) Cost-effective solution Robust design

    Witt&Sohn AG Oct-1414

  • For Fan Maker: None stall-free fan curve

    with shown stall area Cumulative fan curve of parallel fans

    Requirements for Parallel Operation

    Cumulative fan curve of parallel fans

    INFO:

    Most fan makers do not know/ show the STALL area characteristic of their fans! (stall control impossible)

    Witt&Sohn AG Oct-1415

    (stall control impossible)

  • For Fan Maker: None stall-free fan curve

    with shown stall area Cumulative fan curve of parallel fans

    Requirements for Parallel Operation

    Cumulative fan curve of parallel fans

    or

    Stall-free fan curve

    Witt&Sohn AG Oct-1416

  • Stall & Parallel Operation

    1. Definition of Stall

    CONTENT

    2. Requirements for Parallel Operation

    3. Operation of Parallel Fans

    4. Stall-free Fans & VSD

    Witt&Sohn AG Oct-1417

  • Installation: Keep distance between fans to prevent disturbance and interference of

    fans

    Operation of Parallel Fans

    Bad Good

    Witt&Sohn AG Oct-1418

  • Installation: Connect to plenum with separation walls Ensure symmetric openings Use shut-off dampers at one side

    Operation of Parallel Fans

    Use shut-off dampers at one side

    Bad Good

    symmetric openings

    asymmetric opening

    Witt&Sohn AG Oct-1419

    separation wall

    openings

    short circuit of flow

  • Installation - Samples:

    Operation of Parallel Fans

    Witt&Sohn AG Oct-1420

  • Operation of Parallel Fans

    Parallel Fan OperationI. Start in cascade (DOL, weak supply net)

    synchronize fan start with opening of dampersynchronize fan start with opening of damper1. ensure all dampers are initially closed2. start-up 1st fan 3. wait for signals

    1st fan: full speed and 1st damper: open4. start-up next fan (step 2. to 4.)stop procedure with any notice of failure

    But:

    Witt&Sohn AG Oct-1421

    But:

  • Operation of Parallel Fans

    Problem:Switch on an additional fan might lead to Asymmetry of individual air flow Asymmetry of individual air flow Moving of duty point of remaining fans into stall area Uncontrollable pulsing of system System performance problems Fan damage

    Witt&Sohn AG Oct-1422

  • Operation of Parallel Fans

    Parallel Fan OperationII. Start in parallel (DOL, strong supply net)

    synchronize fan start with opening of dampersynchronize fan start with opening of damper1. ensure all dampers are initially closed2. start-up all fans simultaneously 3. wait for signals

    all fans: full speed and all dampers: openstop procedure with any notice of failure

    But difficult to achieve Requires strong supply net

    Witt&Sohn AG Oct-1423

    Requires strong supply net

  • Operation of Parallel Fans

    Parallel Fan OperationIII. Start-up in parallel (VSD)

    synchronize fan start with opening of dampersynchronize fan start with opening of damper1. ensure all dampers are initially closed2. start-up all fans simultaneously:

    use 1st VSD as master, others as slave(AOmaster: actual speed AIslave: speed set point)

    3. wait for signals all fans: full speed and all dampers: open

    stop procedure with any notice of failure

    But expensive

    Witt&Sohn AG Oct-1424

    But expensive

  • Stall & Parallel Operation

    1. Definition of Stall

    CONTENT

    1. Definition of Stall

    2. Requirements for Parallel Operation

    3. Operation of Parallel Fans

    4. Stall-free Fans & VSD

    Witt&Sohn AG Oct-1425

  • Stall-free Fans & VSD

    Stall-free fans by WITT&SOHNWITT&SOHN :1. Fans with truly STALL-free fan curve

    No limitation during parallel duty No limitation during parallel duty(trouble free)

    Max. stability against pressure pulses

    Witt&Sohn AG Oct-1426

  • Stall-free Fans & VSD

    Stall-free fans by WITT&SOHNWITT&SOHN :2. Fans with Anti-Stall Device and

    quasi STALL-free fan curve

    Still limitation during parallel duty:

    Anti-Stall Device

    Still limitation during parallel duty:Anti-stall device reduces effect of stall,but continuous operation in stabilized areanot recommended

    High stability against pressure pulses

    Provides a significant higher level of reliability of the ventilation system

    Parallel operation(trouble-free)

    Witt&Sohn AG Oct-1427

    reliability of the ventilation system

  • Stall-free Fans & VSD

    Stall-free fans by WITTWITT&&SOHNSOHN :3. Fans with STALL-free fan curve and VSD

    Multiple duty points achievable with one blade angle

    Constantly high efficiencies

    No complex pitch-in-motion impellers required

    Witt&Sohn AG Oct-1428

  • Summary

    Axial flow fans should not be operated in STALL or in the stabilized STALL area Piston effects have to be taken into account Stall can be detected by a Petermann probe Stall can be detected by a Petermann probe Parallel duty is restricting the operation range of fans with none stall-free

    characteristics For parallel duty it is required t