VARIMARK II CENTRIFUGAL FANVOLUME CONTROL

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INTRODUCTION

CENTRIFUGAL FANMODULATING DEVICE

Because of the emphasis put onenergy savings, variable volumeair flow is now required for mostnew buildings or when renovat-ing old ones.

To meet these modern technicalneeds, Rosemex has available aunique patented centrifugal fanmodulating device, the Varimark ll.

Canadian Patent No. 1044672U.S. Patent No. 4135850Patent applied for in othercountries.

INDEX

Application Features ................... 3

Physical Features .................... 4-5

Variable AirVolume Systems ................. 6-7

PerformanceVarimark ll ........................... 7-8

Controls ...................................... 9

Dimensions ............................... 10

Specifications ........................... 11

3

APPLICATION FEATURES

THE VARIMARK ll

An approach to variable air vol-ume control system that has noequal.

Designed on the principle that areduction of the effective width ofa Backwardly Inclined or Airfoilcentrifugal fan wheel decreasesboth the CFM and SP, theVarimark ll consists of cylindricaldampers sliding over the wheel.This patented device, developedby Rosemex, offers a degree ofefficiency, accuracy, flexibilityand long life unmatched by anyexisting mechanism in the sameprice range. Activated by pres-sure sensors in the duct work,the Varimark ll decreases air vol-ume from 100% to 20% whilemaintaining fan high efficiencythroughout the complete operat-ing range.

FEATURES OFTHE VARIMARK ll

• Eliminates fan surge and sys-tem instability.

• Energy savings are realizednot only on fan operation, butmost important by reducingload on chiller and boiler.

• Superior acoustical perfor-mance since the most efficientfan for the job is selected.

• Rugged, maintenance-freemechanism .

• Low pressure control air line(only 20 PSI) is needed forVarimark ll operation even onlarge size fan.

• The ideal solution for retro-fitting existing fans.

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PHYSICAL FEATURES

CYLINDRICALDAMPERS

On fans from 12’’ to 44’’ diame-ter, Varimark ll dampers aremade of sheet steel and from49’’ diameter up, aluminum alloysheet is used. Dampers are rein-forced by rings, channel ringsand cross channels as requiredfor the different blower classes.

DAMPER CARRIAGESAND GUIDE TUBES

Each damper is supported bytwo carriages, 180° apart, andon each carriage are mounted 4polyurethane rollers turning onpermanently sealed and greasedball bearings. On fans 22’’ diam-eter and larger, two roller shaftsout of four per carriage areeccentric to allow for play adjust-ment. The carriages and theirdamper travel back and forth ontwo guide tubes made from elec-trically welded, chrome platedtubing. Both tube ends are firmlybolted to the fan casing.

On DWDI fans 36’’ diameter andlarger, a reinforcing tube isadded for each guide tube.

DAMPER OPTIONS

Varimark ll is normally closed;normally open option is availableupon request.

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PHYSICAL FEATURES

DRIVE MECHANISM

A positioning rod has one endfastened to the pneumatic oper-ator and the other end to one ofthe damper carriages.

On DWDI fans, the action of thepositioning rod on the carriage istransferred to the adjacent car-riage of the other damperthrough a rack and pinion mech-anism. This mechanism is sup-ported and protected by a heavygauge steel housing. Racks andpinion are chrome plated andthe pinion rotates on a nylonbushing. Complete travel rangewill take dampers from center ofwheel (closed position) to eachside of fan casing, thus com-pletely uncovering wheel (openposition).

On SWSI fans, only one cylindri-cal damper is used, eliminatingthe need of racks and pinion.The positioning rod pushes orpulls the damper to cover(closed position) or uncover(open position) the wheel.

PNEUMATICOPERATOR BRACKET

Pneumatic operator bracketsvary to accept most makes ofoperators. Lever mechanismusing 1 3/16’’ diameter S.A.E.1045 shafting, mounted onsealed flange ball bearings,transfers operator movement topositioning rod with a minimumof friction loss.

PNEUMATIC OPERATOR

For choice of pneumatic opera-tor, consult your local Rosemexrepresentative.

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VARIABLE AIR VOLUME SYSTEMS

Being more sophisticated thanconventional systems due towide fluctuations of air volume,VAV systems require morecare in choosing both the fans

and their modulating devices.Furthermore, the operation ofVAV terminal units cause thesystem curve to be modifiedand shifted away from the

point of zero SP and zero CFMto the minimum SP required forefficient operation of theseunits.

CENTRIFUGAL FAN MODULATING DEVICES

VARIABLE SPEED FANS

This method of air flow reductionshould bring a reduction in BHPin a certain modulation range,providing the savings are notneutralized by the high initialcost and by the power consump-

tion of the variable speed drive. However, with such a device,selecting the most efficient fanfor the job is nearly impossiblebecause surge area is encoun-tered rapidly, therefore reducing

the modulation range. Thisdrawback forces the use of asmaller fan at lower efficiency(higher BHP) and higher noiselevel.

The addition of a variable inletvane increases the noise levelof a centrifugal fan even whenthe most efficient one is select-ed. The surge area appears

rapidly with this most efficientfan, and the same compromiseas with the variable speed fan isnecessary, that is the selectionof a smaller fan at higher speed

in order to obtain a reasonablemodulation range. The disad-vantages of the smaller fan arethe same as with the variablespeed drive.

VARIABLE INLET VANES

NOTE: A FAN SHOULD NEVER BE SELECTED OR ALLOWED TO OPERATE IN THE SURGE AREA (REFER TO ASHRAE TRANSACTIONS 1977 PART ONE).

MODULATIONRANGE

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LARGEFAN

MODULATIONRANGE

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MEDIUMFAN

MODULATIONRANGE

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SMALLFAN

MODULATIONRANGE

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LARGEFAN

MODULATIONRANGE

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MEDIUMFAN

MODULATIONRANGE

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SMALLFAN

MODULATION RANGE WITH INLET VANES

MODULATION RANGE WITH VARIABLE SPEED FANS

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PERFORMANCE

Because of the Varimark II prin-ciple, operation in the limitedsurge area will not occur, thuspermitting selection of the large,most efficient and quiet fan withfull modulation range.

Standard Varimark II permits fanoperation in a stable area frommaximum air flow rate down tofull closure. In the fully closedposition, the CFM leakage is20%.

MODULATION RANGE WITHVARIMARK II

FAN PERFORMANCE CURVE

VARIMARK II

In calculating energy cost,knowing the utilization profile ofthe fan is of prime importance.When controlling a VAV systemwith a Varimark II, the fan is cho-sen directly from the fan curvecatalogue. Maximum CFM pub-lished for a given fan curve rep-resents 90% of WOCFM. Nocorrection factor is required forRPM and BHP.

EXAMPLE:

Fan size: 36’’ Bl - DWDIMax. req. CFM: 42000SP: 6’’ max. - 1.5’’ min.— Find CFM, SP and BHP at75%, 50%, 25% and 12.5%openings of Varimark II.

1) On the fan performancecurve, at 42000 CFM and 6’’ SP,read 1197 RPM and 55.7 BHP.At 90% WOCFM and 1197RPM, this fan will deliver 58300CFM.

VARIMARK II

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FULL MODULATION RANGE

2) Calculate ratio of maximumrequired CFM over 90%WOCFM:

Max. req. CFM 42000= = 72%

90% WOCFM 58300

42000 58300AIR FLOW

45090% WOCFM

1200

1650

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PERFORMANCE

3) On fig. A, from the 72% pointon the 90% WOCFM curve, drawa vertical line up to the 100%damper opening curve, and ahorizontal line to read the equiva-lent maximum pressure: 75%.

4) Since the minimum requiredpressure is 1.5’’, using the ruleof three, the equivalent mini-mum pressure will be:

1.5’’x 75% = 18.7%

6’’

On fig. A, plot a system curvebetween the equivalent minimumpressure point (18.7%) on the SPscale and the operating point onthe 100% damper opening curve.

5) We can now read pressureand flow percentages for eachdamper opening position:

6) The 72% CFM and 75% SPobtained for the full damperopening represent 100% CFMand 100% SP for this system.Using the rule of three, translatethe partial damper opening per-centages of step no. 5 as follows:

Translate flow % =

100% x Partial flow %

Max. flow %

100% x 67% = 93%

72%

and so forth

Translate pressure % =

100% x Partial pressure %

Max. pressure %

100% x 67% = 89%

75%

and so forthTherefore:

7) On fig. B, read the relativeBHP using the relative CFMcalculated in step 6.

8) Apply the results of step 6and 7 on 36’’ Bl DWDI fan per-formance.

100 %VARIM

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SCALE OF 90 % WOCFM

SCALE OF 100 % WOCFM

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90

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% CFM0 10 20 30 40 50 60 70 80 90 100

10 20 30 40 50 60 70 80 90 100

10 20 30 40 50 60 70 80 90 100 110

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75 %

50 %

25 %

12.5 %CL

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HP

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Damperopening CFM SP BHP

100% 42000 6.0 55.775% 39000 5.3 53.450% 34400 4.4 49.525% 26900 3.2 42.9

12.5% 19700 2.4 35.1

% Opening CFM SP100% 72% 75%75% 67% 67%50% 59% 55%25% 46% 40%

12.5% 34% 30%

Damper opening CFM SP100% 100% 100%75% 93% 89%50% 82% 73%25% 64% 53%

12.5% 47% 40%

Damper opening CFM BHP100% 100% 100%75% 93% 96%50% 82% 89%25% 64% 77%

12.5% 47% 63%

VARIMARK II PERFORMANCE

FIGURE A FIGURE B

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CONTROLS

Controls are a very importantpart of a VAV system, and thechoice of components is criticalif maximum efficiency is to beobtained from all the elements ofthis system.

The following items should bechosen with particular care:

• Sensors: type (electric.... pneu-matic), quantity and location.Generally speaking, sensorshould be installed at 2/3 thelength of duct work.

• Controller: accuracy, quantity.

• Pilot positioner: accuracy.

• Tubing (if pneumatic): lengthand size affect response time.

• Supply and return fans: shouldbe controlled by the same sen-sor to cycle simultaneously.

NOTE: — OUTPUT OF EACH ZONESHOULD BE APPROXIMATELYTHE SAME FOR GOOD MODU-LATION.

EXAMPLE OFVAV SYSTEMWITH CONTROLS

A - Actuator pneumaticoperator

M - Main control air supply- 20 PSI

MPSR - Minimum pressureselector relay

P - Pilot positionerPC - Receiver controllerPSR - Pressure selector relayPST - Pressure sensor trans-

mitterST - Pressure sensor

AIR SYSTEM CONTROL SYSTEM

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SUPPLY FAN

VAV BOXES

RETURN FAN

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PM

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MPSRM

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PCM

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PST

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PSR

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PCM

PST

ST

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PSR

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PCM

PST

ST

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PSR

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PCM

PST

ST

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PSR

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PCM

PST

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HIGHLIMIT LOW LIMIT

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ALL VAV SYSTEMS HAVE THEIR PARTICULARITIES. THIS EXAMPLE IS ONLY GIVEN ASA GUIDE. FOR COMPLETE INFORMATION ON VAV CONTROLS,

CONSULT YOUR CONTROL MANUFACTURER.

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DIMENSIONS

A A

VARIMARK IICYLINDRICALDAMPER

POSITIONINGROD

CARRIAGE GUIDE TUBE

DAMPERCARRIAGE

OPERATOR BRACKET ANDLINKAGE

PNEUMATICOPERATOR ANDPOSITIONER

PNEUMATICOPERATOR

PNEUMATICOPERATOR

MOTOR POSITIONY OR Z

MOTOR POSITIONW OR X

DOUBLEWIDTH

SINGLEWIDTH

CLOCKWISE ARRANGEMENTS‘‘UBD’’ SHOWN

ALL OTHER STANDARDARRANGEMENTS ARE

AVAILABLE

1) Pneumatic operator is always installed on electric motor side of fan casing except when specifications require operator installation on other sideof casing.On cabinet fans with electric motor outside cabinet, operator is always installed outside on cabinet, on electric motor side.When electric motor is inside cabinet, operator is always installed inside, opposite side from electric motor.

2) Dimensions are as per current manufacture. Future changes may be shown on approval drawings only.

3) Varimark II weight includes all mechanism parts and pneumatic operator.

SI DATA

UNIT NO. 12 13 15 16 18 20 22 24 27 30 33 36 40 44 49 54 60 66 73

A mm 457 457 457 483 483 508 508 533 533 559 559 584 584 610 635 660 711 762 838

44 45 45 46 47 48 53 57 59 62 66 77 81 87 105 112 121 154 178

55 57 59 61 62 64 84 88 93 98 108 122 131 138 170 186 208 264 304

SWSIkg

DWDIkgW

EIG

HT

IMPERIAL DATA

UNIT NO. 12 13 15 16 18 20 22 24 27 30 33 36 40 44 49 54 60 66 73

A inches 18 18 18 19 19 20 20 21 21 22 22 23 23 24 25 26 28 30 33

98 99 100 102 103 107 118 126 131 138 145 170 179 192 231 248 268 341 393

122 126 130 134 138 143 186 195 205 217 238 269 289 305 376 410 459 583 672

SWSIlb

DWDIlbW

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SPECIFICATIONS

GENERAL

The mechanical contractor shallfurnish and install fans completewith Varimark ll as shown on theplans. Fan specifications shallbe as per centrifugal fan cata-logue.

VARIMARK llCYLINDRICALDAMPERS

On fans from 12’’ to 44’’ diame-ter, dampers shall be fabricatedof sheet steel with reinforcingrings on both sides. On fansfrom 49’’ diameter and up,dampers shall be made of sheetaluminum alloy, reinforced byaluminum rings and cross chan-nels.

DAMPER CARRIAGES

Dampers shall be supported bycarriages on which shall bemounted 4 polyurethane rollersturning on permanently sealedand greased ball bearings. Onfans 22’’ diameter and larger,lower roller shafts shall beadjustable.

CARRIAGEGUIDE TUBES

Damper carriages shall travel onelectrically welded chrome plat-ed guide tubes. On DWDI fans,36’’ diameter and up, a reinforc-ing tube shall be added for eachguide tube.

DRIVE MECHANISM

On DWDI fans, a positioning rodand a chrome plated rack andpinion mechanism shall operatethe Varimark II dampers. Thepinion shall rotate on an oil-impregnated bronze bushingand the mechanism shall besupported and protected by asteel housing.

On SWSI fans, a positioning rodshall operate the Varimark IIdamper.

PNEUMATICOPERATOR BRACKET

The operator shall be mountedon a heavy gauge steel bracketdesigned to receive mostmakes. Operator action shall betransferred to the positioning rodthrough a lever mechanismmounted on a sealed flange ballbearing.

PNEUMATICOPERATOR

Operator recommended byRosemex Engineering Depart-ment shall be supplied completewith positive feed back position-er to control the Varimark II.

The control contractor shall pro-vide 20 PSI main air line to thefan control system.

PRINTED IN CANADA

MARK-H FAB

1560, Marie-Victorin blvdSaint-Bruno (Quebec)J3V 6B9Tel.: (514) 653-1002Fax: (514) 653-3464

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