AMCA International Technical Seminar 2009

PLENUM FANS

Terminology, History, Testing, Application and Trends Presented by: John Cermak, Acme Engineering & Manufacturing Corp .

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.

Learning Objectives

• • • • • •

Understand terminology and classification Learn plenum fan characteristic features Understand air and sound performance testing Understand how to apply the test data Understand principle advantages and limitations in application Learn the trends in development of applications

TERMINOLOGY

• • • Plenum fans are a part of the group of fans called

centrifugal fans All

centrifugal fans have

centrifugal impellers

but some subgroups have housings, some have not The

centerpiece

of centrifugal fans are fans with scroll housing and they are called centrifugal fans

AMCA CERTIFIED RATING PROGRAM

• recognizes as centrifugal fans also: • In-line centrifugal fans • Plug fans

Plenum fans

SW CENTRIFUGAL IMPELLERS

• With Airfoil Blades

SW CENTRIFUGAL IMPELLERS

• With single thickness backward curved blades

IN-LINE CENTRIFUGAL FAN

• With cylindrical housing

IN-LINE CENTRIFUGAL FAN

• With box housing

PLUG FAN

• Plug fan may or may have not scroll housing (here without housing)

PLENUM FAN

• Horizontal Arr.3, Flanged Inlet

PLENUM FAN

• Horizontal Arr3. With Upper Frame

ARRANGEMENT 1

Can include vibration islolators

ARRANGEMENT 3

Can include vibration islolators

ARRANGEMENT 4

• Arrangement 4 (direct drive) is not specifically mentioned in the CRP but the CRP8 form has a provision for this case

HISTORY

• • • Centrifugal fan with scroll housing inside of a cabinet presented a temptation for

cost reduction

Scroll housing was relatively expensive, cost reduction substantial Doubts about a good

air performance

plenum fans led to a slow pace in their of applications

HISTORY

• • Usage of

wide

in fan size and centrifugal impellers - reduction

low fan efficiency

– this consequence was more devastating for plenum fans than for centrifugal fan with scroll housing Impellers for plenum fans are mostly identical to those used in centrifugal fans with scroll housings yet in

plenum fans

there is no housing and the air leaves the fan at substantially

higher velocity

HISTORY

• Plenum fans opened the opportunity for application of centrifugal impellers with

backward curved blades

in air handling equipment -

higher efficiency and better sound

performance • In the last few years the fan users pay more and more attention to

low sound

INSTALLATION TYPE A

Free Inlet/Free Outlet

INSTALLATION TYPE C

Ducted Inlet/Free Outlet

AIR PERFORMANCE TESTING

Typical setup with plenum fan outside of the test chamber

TESTED FAN AIR TEST CHAMBER FLOW AUXILIARY FAN

SOUND TESTING

Testing of outlet sound

SOUND TEST CHAMBER SILENCERS FLOW TESTED FAN

SOUND TESTING

Testing of inlet sound

SOUND TEST CHAMBER TESTED FAN SILENCERS FLOW

APPLICATION

• • • • • Important condition for successful application of plenum fans is the knowledge of:

Test configuration Test uncertainties and tolerances Application uncertainties

O.E.M applications are generally safer since the equipment is tested as a part of R&D process

APPLICATION OF TEST DATA

The air performance and sound data based on tests can be applied to the fans only if the

fan/ducts configuration of tests

and in the

application are the same

• • • •

APPLICATION OF TEST DATA

Free or Ducted Inlet Free Outlet

does do not create any controversy, During the

test

the fan discharges air into a room, usually large, but smaller than the free space. The shape and the minimum size of that room are not specified Plenum fans are mostly

used

inside of a cabinet which size is much smaller than the room used for testing Incomplete and unreliable application correction data are used

AIR PERFORMANCE

Centrifugal vs. Plenum Fan ( same size and speed ) 5 4 3

Stall Centrifugal Fan Plenum Fan

2 1 0 0 2000 4000 6000 8000

Flow (cfm)

10000 12000 14000 16000

AIR PERFORMANCE

Centrifugal vs. Plenum Fan (same size and speed) 100 90 80 70 60 50 40 30 20 10 0 0

Max Efficiency 55% 70% Centrifugal Fan Plenum Fan BHP Up By 15% 100%

2000 4000 6000 8000

Flow (cfm)

10000 12000 14000 16000

AIR PERFORMANCE

Centrifugal vs. Plenum Fan (same size and speed) 5 4 3 2 1 0 0

Stall Centrifugal Fan Plenum Fan Max Efficiency BHP Up By 15%

2000 4000 6000 8000

Flow (cfm)

10000 12000 14000 16000

IMPELLER DISCHARGE VELOCITY

Absolute Velocity Radial Tangential CCW Rotation

FAN DISCHARGE VELOCITY

Centrifugal vs. Plenum Fan ( same size and speed )

2000 3000 4000 5000 Flow (cfm) 6000 7000 8000 9000 Best Efficiency 10000 11000 12000 Discharge Velocity (fpm) 4000 3500 3000 2500 2000 1500 1000 500 0 Ho Ple use num d F an Fa n

PLENUM AS MIXING DEVICE

• •

Well designed plenum

and the position of the plenum fan inside the plenum can enhance the fan performance

Mixing process

of the flow from the wheel and the air inside of the plenum improves usage of filters and or coils located downstream of the fan

PRINCIPLE APPLICATION

• Plenum fans are mostly, but not exclusively used in

air handling units

• Plenum fans are

short in length

to vane-axial or centrifugal fans compared • On the down-stream side of the fan the plenum fans allow length saving installation of the equipment requiring good air velocity distribution across their face area

IMPACT OF MIXING

INLET vs. DISCHARGE SOUND

90 88 86 84 82 80 78 76 1 2 3 Octave Bands 4 7 dB 5 6 7 8

SOUND vs. PERFORMANCE

SWL (dB) 97 96 95 94 93 92 91 90 89 88 1 2 3 4 Octave Bands 5 6 7 8 14000 13640 12000 10000 Flow (cfm) 8000

SPECIFIC SWL

Specific SWL 55.0

Lowest Sound Highest Efficiency 50.0

45.0

40.0

35.0

30.0

1 2 3 4 Octave Bands 5 6 7 8 Mid Mid Free Deliv Low Top Best SE Position on Pressure Curve

PLENUM FAN APPLICATION

5

Stall Max Efficiency Low Sound

4 3 2 1 0 0

Good For Application BHP Up By 15% 50% 100% 70%

2000 4000 6000 8000

Flow (cfm)

10000 12000 14000 16000

CLASSES FOR PLENUM FANS

• • AMCA Class Classification for plenum fans

does not exist

Industry uses the

same

impellers for centrifugal fans with the scroll housing as for plenum fans and applies the same speed ranges for both product lines

CLASSES FOR PLENUM FANS

• Outlet velocity of a centrifugal fan with the scroll housing is quite different from the plenum fan of the same size at the same speed and at the same flow

TRENDS

• • • The

newest

trend is going towards:

Direct drives

(Arrangment 4) Usage of

variable frequency drives

Applications with sometimes called

multiple plenum fans fan walls

DIRECT DRIVE FANS

VFD – Positive Side

• Offers air performance flexibility • Changes the flow as required • Allows for easy monitoring of fan operation • Eliminates cost and maintenance of drives • Offers compact and rigid design

VFD – Negative Side

• Requires good electrical grounding of motor or motor bearing protection against arcing • May require non-stock motor • May not deliver expected power savings • Can be a unpleasant source of sound • Can be an unwanted source of electro magnetic radiation

PLENUM FAN WALL

PLENUM FAN WALLS Positive Side • Reduces length of air-handler • Eliminates drives (sheaves and belts) • Improves sound spectrum • Improves operational reliability • Reduces cost, operation and maintenance costs

PLENUM FAN WALLS Negative Side • Original cost of fans and motors is a concern • Many small fans in parallel operation may lead to in-duct fans rather than plenum fans • Parallel operation of fans should be concern • The set up is very sensitive to non-uniform velocity distribution over the fan wall

PLENUM FAN WALLS Negative Side • Back-draft dampers adding power losses • Using small sizes of fans leads to decrease in their efficiency • Many small fans in parallel operation may lead to in-duct fans rather than plenum fans • Possible vibration problems due to due to excitation of powerful beats with acoustical consequences

PLENUM FANS Conclusion • Plenum fans is advantage is their

mixing flow downstream of the fan

• Plenum fans are excellent for air handlers or cabinet fans having a filter or heat exchanger downstream of the fan • • Plenum fans can develop a

substantial fan pressure

compared to propeller fans

Attractive cost

of plenum fans especially with direct drive

Questions?