PLENUM FANS Terminology, History, Testing, Application and Trends AMCA International Technical Seminar 2009 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 classificationUnderstand terminology and classification Learn plenum fan characteristic featuresLearn plenum fan characteristic features Understand air and sound performance testingUnderstand air and sound performance testing Understand how to apply the test dataUnderstand how to apply the test data Understand principle advantages and limitations in applicationUnderstand principle advantages and limitations in application Learn the trends in development of applicationsLearn 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 of plenum fans led to a slow pace in their applications

HISTORY Usage of wide centrifugal impellers - reduction in fan size and 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 AIR TEST CHAMBER FLOW TESTED FAN AUXILIARY FAN

SOUND TESTING Testing of outlet sound SOUND TEST CHAMBER TESTED FAN SILENCERS FLOW

SOUND TESTING Testing of inlet sound SOUND TEST CHAMBER TESTED FAN FLOW SILENCERS

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 do not create any controversy, Free Outlet does 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 )

AIR PERFORMANCE Centrifugal vs. Plenum Fan (same size and speed)

AIR PERFORMANCE Centrifugal vs. Plenum Fan (same size and speed)

IMPELLER DISCHARGE VELOCITY Radial Absolute Velocity CCW Rotation Tangential

FAN DISCHARGE VELOCITY Centrifugal vs. Plenum Fan ( same size and speed )

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 compared to vane-axial or centrifugal fans 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

SOUND vs. PERFORMANCE

SPECIFIC SWL

PLENUM FAN APPLICATION

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 multiple plenum fans sometimes called 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?