cooling tower operation & maintenance for improved effeciency

Cooling Technology Institute www.cti.org

Cooling Tower Operation and Cooling Tower Operation and Maintenance for Improved Maintenance for Improved

Energy EfficiencyEnergy Efficiency

Russell E. Lindemann


Cooling Tower Operation and Maintenance Cooling Tower Operation and Maintenance for Improved Energy Efficiencyfor Improved Energy Efficiency

Principle of Operation and Layout Principle of Operation and Layout -- Russ LindemannRuss LindemannMaintenanceMaintenance Regimens Regimens -- Randy BradleyRandy Bradley

Operating Strategies & Water Treatment Operating Strategies & Water Treatment -- Paul LindahlPaul Lindahl



Open Cooling TowersOpen Cooling Towers

Closed Circuit Cooling Closed Circuit Cooling TowersTowers

Forced Draft Forced Draft CounterflowCounterflowInduced Draft Induced Draft CounterflowCounterflow

Forced Draft Forced Draft CrossflowCrossflowInduced Draft Induced Draft CrossflowCrossflow



Open Cooling TowerOpen Cooling TowerAn evaporative piece of equipment that exposes An evaporative piece of equipment that exposes water directly to the cooling atmosphere, thereby water directly to the cooling atmosphere, thereby

transferring the source heat load directly to the air.transferring the source heat load directly to the air.



Closed Circuit Cooling TowerClosed Circuit Cooling TowerAn evaporative piece of equipment that contains twoAn evaporative piece of equipment that contains twoseparate fluid circuits. The first is an external circuitseparate fluid circuits. The first is an external circuit

where water is exposed to the atmosphere as itwhere water is exposed to the atmosphere as itcascades over the tubes of a coil bundle. The secondcascades over the tubes of a coil bundle. The secondis an internal circuit in which the fluid to be cooledis an internal circuit in which the fluid to be cooled

circulates inside the tubes of the coil bundle.circulates inside the tubes of the coil bundle.



Forced DraftForced DraftType of mechanical draft tower in which one orType of mechanical draft tower in which one or

more fans are located at the air inlet to force air into more fans are located at the air inlet to force air into the cooling tower.the cooling tower.



Induced DraftInduced DraftType of mechanical draft tower in which one orType of mechanical draft tower in which one or

more fans are located in the air outlet to induce air more fans are located in the air outlet to induce air through the air inlets.through the air inlets.



CounterflowCounterflowIn a In a counterflow counterflow cooling tower, the air enters at thecooling tower, the air enters at the

base of the tower, flows upward and interfacesbase of the tower, flows upward and interfacescounter currently with the falling hot water.counter currently with the falling hot water.



CrossflowCrossflowIn a In a crossflow crossflow cooling tower, the air flowscooling tower, the air flows

horizontally through the cooling tower and interfaceshorizontally through the cooling tower and interfacesperpendicularly with the falling hot water.perpendicularly with the falling hot water.



Water Flow Direction

Air Flow Direction



Air Flow Direction


Fluid Inlet

Fluid Outlet



Air Flow Direction




Air Flow Direction


Fluid Inlet

Fluid Outlet



Air Flow Direction




Water Distribution SystemsWater Distribution Systems–– Gravity distribution systemGravity distribution system–– Spray distribution systemSpray distribution system



Gravity Distribution SystemGravity Distribution System–– Open basinsOpen basins–– Large orifice, 360° nozzlesLarge orifice, 360° nozzles–– Easily accessed for maintenance Easily accessed for maintenance –– Basin water level used to balance flowBasin water level used to balance flow



Spray Distribution SystemSpray Distribution System–– Pressurized systemPressurized system–– Large orifice, 180° directional nozzlesLarge orifice, 180° directional nozzles–– Spray header and branchesSpray header and branches–– 2 PSI spray pressure at the header inlet2 PSI spray pressure at the header inlet



Heat Transfer Surface (Fill or Wet Deck)Heat Transfer Surface (Fill or Wet Deck)–– PVC wet deck surfacePVC wet deck surface–– Specialty wet deck materialsSpecialty wet deck materials



PVC SurfacePVC Surface–– Impervious to rot, decay, fungus and biological attackImpervious to rot, decay, fungus and biological attack–– 130°F limitation for 130°F limitation for counterflowcounterflow cooling towerscooling towers–– 120°F limitation for 120°F limitation for crossflowcrossflow cooling towers cooling towers



High Temperature PVC SurfaceHigh Temperature PVC Surface–– Impervious to rot, decay, fungus and biological attackImpervious to rot, decay, fungus and biological attack–– 150°F limitation for 150°F limitation for counterflowcounterflow cooling towerscooling towers–– 135°F limitation for 135°F limitation for crossflowcrossflow cooling towers cooling towers


Air Moving SystemsAir Moving Systems–– Axial fansAxial fans–– Centrifugal fansCentrifugal fans




Axial FansAxial Fans–– Over 80% of cooling towers on HVAC applications use Over 80% of cooling towers on HVAC applications use

axial fansaxial fans–– High volume/ Low static pressureHigh volume/ Low static pressure–– High efficiencyHigh efficiency–– Low energy consumptionLow energy consumption–– Improved sound ratingsImproved sound ratings



Centrifugal FansCentrifugal Fans–– High volume/Static pressuresHigh volume/Static pressures

–– Indoor installationsIndoor installations–– Inlet or discharge ductworkInlet or discharge ductwork

–– High energy consumptionHigh energy consumption–– Quiet operationQuiet operation–– Tight layout requirementsTight layout requirements



1,500 GPM of Water1,500 GPM of Water95°F EWT95°F EWT85°F LWT85°F LWT78°F EWB78°F EWB

CounterflowCounterflow, centrifugal , centrifugal fan unit requires 60 HPfan unit requires 60 HPCrossflowCrossflow, axial fan unit , axial fan unit requires 30 HPrequires 30 HPAxial fan units require less Axial fan units require less HP than centrifugal fan HP than centrifugal fan unitsunits


Drive SystemsDrive Systems–– Belt driveBelt drive–– Gear driveGear drive




Proven performance on cooling Proven performance on cooling tower applicationtower applicationEfficient and designed for moist Efficient and designed for moist air applicationsair applications



Cooling Tower Equipment LayoutCooling Tower Equipment Layout



Prevent warm air or drift from being introduced into fresh Prevent warm air or drift from being introduced into fresh air intakes or from being carried over populated areasair intakes or from being carried over populated areasConsider the potential for plumeConsider the potential for plumeNote the direction of the prevailing windsNote the direction of the prevailing windsEnsure adequate supply of fresh air to the air intakeEnsure adequate supply of fresh air to the air intakeProvide adequate space for piping and proper servicing and Provide adequate space for piping and proper servicing and maintenancemaintenanceTop of the unit discharge must be at least level with the Top of the unit discharge must be at least level with the adjacent wall adjacent wall



Layout ExamplesLayout Examples–– Adjacent to a wall or buildingAdjacent to a wall or building–– In an enclosureIn an enclosure–– Adjacent to a louvered or slotted wallAdjacent to a louvered or slotted wall



NominalNominal–– 1,500 GPM 95/85/781,500 GPM 95/85/78

1°F Recirculation1°F Recirculation–– 1,384 GPM 95/85/791,384 GPM 95/85/79–– 8% 8% DerateDerate

2°F Recirculation2°F Recirculation–– 1,258 GPM 95/85/801,258 GPM 95/85/80–– 19% 19% DerateDerate

Prevailing Wind

Induced DraftCooling Tower



NominalNominal–– 1,500 GPM 95/85/781,500 GPM 95/85/78

1°F Recirculation1°F Recirculation–– 1,500 GPM 1,500 GPM

95.77/85.77/7995.77/85.77/79

2°F Recirculation2°F Recirculation–– 1,500 GPM 1,500 GPM

96.56/86.56/8096.56/86.56/80

Prevailing Wind




Every 1°F Increase in CWT Corresponds to aEvery 1°F Increase in CWT Corresponds to a2% Decrease in Chiller Efficiency2% Decrease in Chiller Efficiency



Correct cooling tower Correct cooling tower installation when installation when located adjacent to a located adjacent to a building or wallbuilding or wall




What is the distance What is the distance between the wall and the between the wall and the air inlet to the cooling air inlet to the cooling tower?tower?–– Maximum air velocity should Maximum air velocity should

not exceed 300 FPMnot exceed 300 FPM–– Air entry envelope consists of Air entry envelope consists of

top and two sidestop and two sides–– Based on 125,900 CFM, an Based on 125,900 CFM, an

inlet height of 10 feet and an inlet height of 10 feet and an air inlet length of 12 feet, the air inlet length of 12 feet, the distance to the wall is 6.5 feetdistance to the wall is 6.5 feet


D



When cooling towers When cooling towers are positioned with air are positioned with air inlets facing each inlets facing each other, the distance other, the distance between cooling between cooling towers is 2 x Dtowers is 2 x D



What is the distance between What is the distance between the wall and the air inlet to the the wall and the air inlet to the cooling tower for a well cooling tower for a well enclosure?enclosure?–– Maximum air velocity should not Maximum air velocity should not

exceed 400 FPMexceed 400 FPM–– Center the cooling tower within the Center the cooling tower within the

enclosure for uniform air flow to the enclosure for uniform air flow to the air inletsair inlets

–– Air entry is from the top onlyAir entry is from the top only–– Based on 125,900 CFM, an air entry Based on 125,900 CFM, an air entry

area as indicated by the shaded area, area as indicated by the shaded area, the distance to the wall is 8 feetthe distance to the wall is 8 feet

D D

Well Installation with anInduced Draft Cooling Tower



D D

Louvered Well Installation with anInduced Draft Cooling Tower

What is the distance between What is the distance between the louvered wall and the air the louvered wall and the air inlet to the cooling tower for a inlet to the cooling tower for a well enclosure?well enclosure?–– Center the cooling tower within the Center the cooling tower within the

enclosure for uniform air flow to the enclosure for uniform air flow to the air inletsair inlets

–– Louver must provide at least 50% net Louver must provide at least 50% net free areafree area

–– Louver air velocity should not exceed Louver air velocity should not exceed 600 FPM600 FPM

–– Maintain at least 3 feet between the Maintain at least 3 feet between the tower air inlets and the louvered walltower air inlets and the louvered wall



Maintenance Regimens - Randy Bradley


Maintenance GuidelinesMaintenance Guidelinesforfor

Open Cooling Towers & Open Cooling Towers & Closed Circuit Cooling TowersClosed Circuit Cooling Towers


MAINTENANCEMAINTENANCE

Maintenance and water treatment are Maintenance and water treatment are the most important factors affecting the most important factors affecting the life and energy efficient operation the life and energy efficient operation of evaporative cooling equipment!of evaporative cooling equipment!


MAINTENANCE? Who needs it?MAINTENANCE? Who needs it?


MAINTENANCEMAINTENANCEMaintenance and water treatment are the Maintenance and water treatment are the most neglected regimens of cooling most neglected regimens of cooling tower operation, and cooling towers are tower operation, and cooling towers are generally the most neglected generally the most neglected components in the mechanical system.components in the mechanical system.

Why?Why?•• Remotely located & difficult to accessRemotely located & difficult to access•• Limited maintenance resourcesLimited maintenance resources

PeoplePeopleTrainingTrainingBudgetsBudgets


MAINTENANCEMAINTENANCE

Objectives:Objectives:•• Review basic elements of a good Review basic elements of a good

maintenance regimen.maintenance regimen.•• Develop an understanding of the Develop an understanding of the

costs of poor maintenance on the life costs of poor maintenance on the life & energy efficiency of cooling towers.& energy efficiency of cooling towers.


MAINTENANCE REGIMENSMAINTENANCE REGIMENSReview major cooling tower systems and Review major cooling tower systems and their appropriate maintenance regimens:their appropriate maintenance regimens:

•• Circulating WaterCirculating Water•• Fan and DriveFan and Drive•• Heat Transfer Surface (Fill or Coil)Heat Transfer Surface (Fill or Coil)•• Air Entry LouversAir Entry Louvers•• Drift EliminatorsDrift Eliminators


MAINTENANCE REGIMENSMAINTENANCE REGIMENS

•• Reputable manufacturers provide maintenance Reputable manufacturers provide maintenance instructions and check sheets. It is best to follow instructions and check sheets. It is best to follow the manufacturer’s recommendations!the manufacturer’s recommendations!

•• ASHRAE Handbook also provides a good general ASHRAE Handbook also provides a good general guide.guide.


MAINTENANCE REGIMENSMAINTENANCE REGIMENS•• Manufacturer and ASHRAE Manufacturer and ASHRAE

guidelines are for normal cooling guidelines are for normal cooling season regimens.season regimens.

•• Unusual operating conditions will Unusual operating conditions will require additional operator attention.require additional operator attention.

•• Winter operation and longWinter operation and long--term shutterm shut--down requires additional servicing. down requires additional servicing. Consult the manufacturer.Consult the manufacturer.


MAINTENANCE REGIMEN MAINTENANCE REGIMEN ––Circulating Water System TypesCirculating Water System Types

CrossCross--flow Tower Operation View of Water Distribution Boxflow Tower Operation View of Water Distribution Box

Gravity Flow Water Distribution SystemGravity Flow Water Distribution SystemCommon to crossCommon to cross--flow cooling towers.flow cooling towers.


MAINTENANCE REGIMEN MAINTENANCE REGIMEN ––Circulating Water System TypesCirculating Water System Types

Closed Circuit Tower View of Pressurized DistributionClosed Circuit Tower View of Pressurized DistributionOperation System and NozzlesOperation System and Nozzles

Pressurized Flow Water Distribution SystemPressurized Flow Water Distribution System


MAINTENANCE REGIMEN MAINTENANCE REGIMEN ––Circulating Water SystemCirculating Water System

Spray Nozzles & Water Distribution Boxes Spray Nozzles & Water Distribution Boxes need to be inspected & cleanedneed to be inspected & cleaned

•• After startAfter start--up and up and •• Monthly thereafter.Monthly thereafter.Regular inspection allows quick treatment Regular inspection allows quick treatment

and control of corrosion and mechanical and control of corrosion and mechanical failures. failures.



Clogged distribution nozzles cause:Clogged distribution nozzles cause:•• Reduced or malReduced or mal--distributed water flow = distributed water flow =

capacity reductioncapacity reduction•• Overflowing distribution boxes = water & Overflowing distribution boxes = water &

chemical losschemical loss•• Heat Exchanger surface scaling/fouling = Heat Exchanger surface scaling/fouling =

capacity reductioncapacity reduction•• Excessive drift = water & chemical lossExcessive drift = water & chemical loss•• Fan motor overFan motor over--ampingamping (forced draft) = (forced draft) =

reduced motor lifereduced motor life



Suction Strainers:Suction Strainers:•• Designed to protect pump Designed to protect pump

and nozzles.and nozzles.•• Inspect & clean weekly.Inspect & clean weekly.•• Operating environments Operating environments

laden with airborne fibrous laden with airborne fibrous materials (agricultural, materials (agricultural, paper, textile processing) paper, textile processing) demand more frequent demand more frequent strainer cleaning.strainer cleaning.



Poor Strainer maintenance leads to:Poor Strainer maintenance leads to:••Reduced flow = reduced capacityReduced flow = reduced capacity••Pump Pump cavitation cavitation = pump repair costs and = pump repair costs and objectionable plant noiseobjectionable plant noise••Collapsed strainers = tower repair costsCollapsed strainers = tower repair costs



Basin Maintenance:Basin Maintenance:••Clean and flush monthly.Clean and flush monthly.••Inspect and repair corrosion.Inspect and repair corrosion.Accumulated solids:Accumulated solids:Clog equalizer & bypass linesClog equalizer & bypass linesHide corrosion cellsHide corrosion cellsGive breeding environment for bioGive breeding environment for bio--growthgrowth



Closed Circuit Tower Water Pumps:Closed Circuit Tower Water Pumps:••Inspect seals & free rotation of shaft monthly.Inspect seals & free rotation of shaft monthly.••Lubricate bearings per motor manufacturer Lubricate bearings per motor manufacturer instructions.instructions.

Leaking seals are costly Leaking seals are costly with lost water and with lost water and treatment chemicals.treatment chemicals.



MakeMake--up water and operating level controlsup water and operating level controls

Mechanical Float Valve Mechanical Float Valve Electric Valve & SensorElectric Valve & Sensor



Set operating level and water supply pressure to Set operating level and water supply pressure to manufacturer’s recommendations.manufacturer’s recommendations.

••Inspect water level and adjust float monthly.Inspect water level and adjust float monthly.

••Inspect valve seals and full shutInspect valve seals and full shut--off monthly.off monthly.

Clean electronic sensing elements as required. Clean electronic sensing elements as required.



Malfunctioning level Malfunctioning level control can be costly with control can be costly with water and chemical loss water and chemical loss and even equipment and even equipment damage.damage.

Proper water level control is required for pump Proper water level control is required for pump priming and prevention of air entrainment in priming and prevention of air entrainment in suction lines.suction lines.


MAINTENANCE REGIMEN MAINTENANCE REGIMEN ––Fan & Drive SystemFan & Drive System

The fan system moves the air which cools the The fan system moves the air which cools the water. water. It is critical to keep the fan system It is critical to keep the fan system in top operating condition!in top operating condition!

••Daily walk around the tower and listen for unusual Daily walk around the tower and listen for unusual noises or vibration.noises or vibration.••If reasons for vibration are easily detected, (loose belts, If reasons for vibration are easily detected, (loose belts, loose motor base, loose bearing locking collars, loose loose motor base, loose bearing locking collars, loose fan or sheave bushings) correct as required.fan or sheave bushings) correct as required.••If causes of vibration are not easily detected, consult a If causes of vibration are not easily detected, consult a specialty vibration analysis contractor.specialty vibration analysis contractor.



•• Quarterly clean fan of heavy debris (trash, Quarterly clean fan of heavy debris (trash, bird droppings, scale) and inspect the fan bird droppings, scale) and inspect the fan and drive components for tight fasteners, and drive components for tight fasteners, missing balance washers & structural missing balance washers & structural integrity. integrity. •• Repair or replace corroded hardware, even Repair or replace corroded hardware, even the fan if necessary. the fan if necessary. •• Check the mechanical equipment support Check the mechanical equipment support for cracks and tight hardware.for cracks and tight hardware.•• Check security of fan guards.Check security of fan guards.



Belt Drive Systems:Belt Drive Systems:Belt Tensioning:Belt Tensioning:Check 24 hrs after startCheck 24 hrs after start--up.up.

Check monthly thereafter.Check monthly thereafter.

1/2” 1/2” -- 3/4” deflection with 3/4” deflection with moderate finger pressure at moderate finger pressure at center span of belt. Check center span of belt. Check manufacturer’s O&M guide.manufacturer’s O&M guide.



Gear Drive Systems:Gear Drive Systems:Lubrication:Lubrication:Check oil level weekly.Check oil level weekly.Change oil 500 hours or Change oil 500 hours or 4 weeks after start4 weeks after start--up. up. Follow gear box O&M Follow gear box O&M guide for oil type and guide for oil type and change frequency. change frequency. Recommend synthetic, Recommend synthetic, oxidation inhibited oil.oxidation inhibited oil.



Gear Drive Systems:Gear Drive Systems: Drive Shafts:Drive Shafts:••Inspect drive shaft Inspect drive shaft and coupling and coupling hardware monthly.hardware monthly.

••Inspect coupling flex Inspect coupling flex elements for buckling elements for buckling and fatigue damage. and fatigue damage. Replace as required.Replace as required.

Drive shaft CouplingDrive shaft Coupling



Fan Shaft Bearings:Fan Shaft Bearings:Bearing Lubrication:Bearing Lubrication:Lubrication ScheduleLubrication Schedule•• 1000 hours or 3 months 1000 hours or 3 months -------- Induced DraftInduced Draft•• 2000 hours or 6 months 2000 hours or 6 months -------- Forced DraftForced Draft•• Use water resistant Use water resistant grease approved by grease approved by manufacturer.manufacturer.



Motors:Motors:Good maintenance starts with the installationGood maintenance starts with the installation1. Wire per nameplate and check rotation1. Wire per nameplate and check rotation•• MultiMulti--lead (9, 12 wire) motors may be confusinglead (9, 12 wire) motors may be confusing•• Check multiCheck multi--speed motor rotation at both speedsspeed motor rotation at both speeds•• Check current draw on startCheck current draw on start--upup2. Check2. Check operational controlsoperational controls•• Set proper time delay between speed changesSet proper time delay between speed changes•• Set thermostat differentials to limit fan cycling Set thermostat differentials to limit fan cycling

(3(3--6 starts/hour)6 starts/hour)



Motors:Motors:Motor life and efficiency is enhanced byMotor life and efficiency is enhanced by1. Keeping motor body cool1. Keeping motor body cool•• Clean casing and cooling fins of scale buildClean casing and cooling fins of scale build--upup•• Do not obstruct cooling vents around motorDo not obstruct cooling vents around motor2. Properly lubricating motor bearings2. Properly lubricating motor bearings•• Follow motor O&M guide for lubrication intervals, Follow motor O&M guide for lubrication intervals,

typically 2typically 2--3 years, and compatible greases.3 years, and compatible greases.•• Some motors have sealed bearings and do not Some motors have sealed bearings and do not

require lubrication.require lubrication.



Motors:Motors:Motors driven by variable frequency drives (Motors driven by variable frequency drives (vfdvfd) ) 1. Offer fan energy saving at the cooling tower1. Offer fan energy saving at the cooling tower2. Reduce fan cycling and provide soft starting2. Reduce fan cycling and provide soft starting3. Need to be specifically selected for 3. Need to be specifically selected for vfd vfd dutyduty4. Need limits on length between motor & drive4. Need limits on length between motor & drive

(Depending on drive, typically 50 to 200 feet.)(Depending on drive, typically 50 to 200 feet.)5. Run hotter and need good cooling air5. Run hotter and need good cooling air--flowflow


MAINTENANCE REGIMEN MAINTENANCE REGIMEN ––Heat Transfer SurfaceHeat Transfer Surface

Inspect heat transfer surfaces monthly.Inspect heat transfer surfaces monthly.Inspect both the top Inspect both the top andand bottom. Generally, bottom. Generally, scaling starts on the top and bioscaling starts on the top and bio--fouling builds fouling builds from the bottom. from the bottom.

Open tower surface (fill)Open tower surface (fill) Closed circuit tower coilClosed circuit tower coil



Open Tower Packing (Fill):Open Tower Packing (Fill):••Scale, solids and bioScale, solids and bio--fouling fouling restrict air & water passages.restrict air & water passages.••Capacity diminishes rapidly Capacity diminishes rapidly with increased fouling.with increased fouling.••Extra weight can damage fill Extra weight can damage fill and structural supports.and structural supports.

Typical fill clogging from bioTypical fill clogging from bio--films and suspended solids.films and suspended solids.



Closed Circuit Tower Coil:Closed Circuit Tower Coil:••Scale on coil Scale on coil walls is a direct walls is a direct heat transfer heat transfer barrier. barrier. ••Capacity Capacity diminishes with diminishes with increased fouling.increased fouling.



Closed Circuit Tower CoilClosed Circuit Tower Coil

Closed Circuit Cooling Tower Performance vs. Scale Accumulation on Heat Transfer Coil

40.0%50.0%60.0%70.0%80.0%90.0%

100.0%

0 0.002 0.004 0.006

Fouling Factor & Approximate Scale Thickness On Coil

Tow

er P

erfo

rman

ce

Cap

abili

ty

1/32" Scale 1/16" ScaleClean Tube 3/32" Scale

High Heat Flux Coil

Low Heat Flux Coil

( 0.8 mm ) ( 1.6 mm ) ( 2.4 mm )



Cleaning heavy scale or bioCleaning heavy scale or bio--fouling is difficult.fouling is difficult.Often the fill or coil are damaged in the process.Often the fill or coil are damaged in the process.

IT IS ESSENTIAL TO MAINTAIN A IT IS ESSENTIAL TO MAINTAIN A PREVENTATIVEPREVENTATIVE WATER TREATMENT WATER TREATMENT PROGRAM.PROGRAM.

Results of a scaled coilResults of a scaled coilcleaned with acid. Thiscleaned with acid. Thiscoil is ruined.coil is ruined.


MAINTENANCE REGIMEN MAINTENANCE REGIMEN ––Drift EliminatorsDrift Eliminators

Separate water droplets from leaving air streamSeparate water droplets from leaving air stream••Subject to damage from weather & vandalismSubject to damage from weather & vandalism••Subject to corrosionSubject to corrosion

Damaged eliminatorDamaged eliminatorsection, which shouldsection, which shouldbe replaced.be replaced.


MAINTENANCE REGIMEN MAINTENANCE REGIMEN ––Drift EliminatorsDrift Eliminators

Proper placement and good physical conditionProper placement and good physical condition••Minimizes water and treatment chemical lossMinimizes water and treatment chemical loss••Minimizes air restriction for maximum capacityMinimizes air restriction for maximum capacity••Minimizes airborne bacterial transmission Minimizes airborne bacterial transmission

Inspect condition and placement monthly.Inspect condition and placement monthly.Remove bioRemove bio--growth and debris. Notify growth and debris. Notify treatment service of biotreatment service of bio--growth. growth. Replace damaged eliminators.Replace damaged eliminators.


MAINTENANCE REGIMEN MAINTENANCE REGIMEN ––Air Inlet LouversAir Inlet Louvers

Examples of scaled, bioExamples of scaled, bio--fouled and debris laden inlet louvers.fouled and debris laden inlet louvers.


MAINTENANCE REGIMEN MAINTENANCE REGIMEN ––Air Inlet LouversAir Inlet Louvers

Proper placement and good physical conditionProper placement and good physical condition••Minimizes water and treatment chemical loss Minimizes water and treatment chemical loss from basin splashfrom basin splash--out.out.••Minimizes air restriction for maximum capacityMinimizes air restriction for maximum capacity••Minimizes airborne bacterial transmission Minimizes airborne bacterial transmission

Inspect condition and placement monthly.Inspect condition and placement monthly.Remove bioRemove bio--growth and debris. Notify growth and debris. Notify treatment service of biotreatment service of bio--growth. growth. Repair damaged louvers.Repair damaged louvers.


Winter OperationWinter OperationMaintenance & Energy Saving TipsMaintenance & Energy Saving Tips

Prevent freezing and expensive ice damage Prevent freezing and expensive ice damage before the winter season arrives:before the winter season arrives:••Check heat tracing and insulation on drains, Check heat tracing and insulation on drains, makemake--up and circulating water lines.up and circulating water lines.••Test basin heaters and controls.Test basin heaters and controls.••Charge coils with glycol or drain completely.Charge coils with glycol or drain completely.••Test operation of positive closure dampers Test operation of positive closure dampers --open with fan on and closed with fan off. open with fan on and closed with fan off.



More tips:More tips:••Do not run fans with pumps off unless basin is Do not run fans with pumps off unless basin is drained. Ensure that fan drives are selected for drained. Ensure that fan drives are selected for dry operation.dry operation.••Interlock heater “off” when pump or fan Interlock heater “off” when pump or fan operates.operates.••Keep a heat load on the tower. Cold water Keep a heat load on the tower. Cold water temperature should stay above 40°F (4.4C) temperature should stay above 40°F (4.4C)



Ice can cause expensive damage to the fill and Ice can cause expensive damage to the fill and tower structure.tower structure.

••Schedule regular Schedule regular defrost cycles.defrost cycles.••Keep water flow in Keep water flow in safe range of the safe range of the distribution nozzle.distribution nozzle.


Maintenance & Energy Efficient OperationMaintenance & Energy Efficient Operation

A basic maintenance regimen is an investment to: A basic maintenance regimen is an investment to: maximize the energy efficiency of the tower and the maximize the energy efficiency of the tower and the

mechanical system,mechanical system,minimize capital investment in equipment by minimize capital investment in equipment by

extending its life and replacement intervals,extending its life and replacement intervals,minimize annual maintenance expenses through minimize annual maintenance expenses through

preventative measures rather than costly repairs.preventative measures rather than costly repairs.

Towers lacking a good maintenance regimen, which Towers lacking a good maintenance regimen, which includes water treatment, routinely operate at well below includes water treatment, routinely operate at well below design capability.design capability.



Operating Strategies and Water Treatment

Paul Lindahl


WHY WATER TREATMENT? WHY WATER TREATMENT?

AirDebrisGases

Air Water

Air and water contents enter and build in the tower.


Biological Growth Biological Growth

Bacteria, AlgaeBacteria, Algae–– Fouling exchangersFouling exchangers–– Fouling Cooling TowerFouling Cooling Tower–– Health Effects, such as Legionnaire’s DiseaseHealth Effects, such as Legionnaire’s Disease

Water TreatmentsWater Treatments–– Oxidizing BiocidesOxidizing Biocides–– NonNon--oxidizing Biocidesoxidizing Biocides

Deposits assist growth of Deposits assist growth of biofilms biofilms and and biofoulingbiofouling, , side stream filtration is recommendedside stream filtration is recommended


CorrosionCorrosion

Consider metals in entire water systemConsider metals in entire water system–– Steel and Iron vs. Stainless SteelSteel and Iron vs. Stainless Steel–– Copper and its AlloysCopper and its Alloys–– AluminumAluminumAppropriate Water Treatments with Appropriate Water Treatments with qualified WT vendor/consultantqualified WT vendor/consultantControl deposition of solids, side stream Control deposition of solids, side stream filtration recommendedfiltration recommended


Deposits Impact CorrosionDeposits Impact Corrosion

CELL METABOLISM LOWERS pH UNDER BIOFILM WHICH CORRODES METAL

Oxide Layer


Deposits Impact CorrosionDeposits Impact Corrosion

PITTING FAILURE

Oxide Layer


MICROBES (MB)

CORROSION DEPOSITION

Each Treatment Impacts the OthersEach Treatment Impacts the Others


Control MethodsControl Methods

BiocideBiocide to reduce Microbe and to reduce Microbe and BiofilmBiofilm Growth Growth [corrosion and scaling effect][corrosion and scaling effect]–– 0.2 to 0.5 0.2 to 0.5 ppm ppm free free Cl Cl residual control range typicalresidual control range typical

InhibitorsInhibitors to protect Metals from Corrosionto protect Metals from CorrosionInhibitorsInhibitors to prevent Scale Precipitationto prevent Scale Precipitation

SurfactantSurfactant = Bio= Bio--penetrationpenetrationAntiAnti--foamfoam = Reduce visible effect of biocide= Reduce visible effect of biocide


Water QualityWater Quality

General GuidelinesGeneral Guidelines: : Note: for tower water, not makeNote: for tower water, not make--upup

High TemperatureHigh Temperature:: < 120 < 120 °°F F PH: 6.5 PH: 6.5 –– 9.09.0Chlorides: < 750 Chlorides: < 750 ppm ppm for Galvanized Steel, for Galvanized Steel, < 1500< 1500 ppmppm for 300 Series Stainless Steelfor 300 Series Stainless SteelCalcium: (as CaCO3) < 800Calcium: (as CaCO3) < 800 ppmppm should not should not result in calcium sulfate scaleresult in calcium sulfate scale



Sulfates: If calcium > 800Sulfates: If calcium > 800 ppmppm, sulfates < , sulfates < 800800 ppmppm (or less in arid climates) to limit (or less in arid climates) to limit scale. scale. –– Otherwise, < 5000Otherwise, < 5000 ppmppm is acceptable. is acceptable.

Silica: < 150Silica: < 150 ppmppm as SiO2 to prevent silica as SiO2 to prevent silica scalescaleIron: < 3 Iron: < 3 ppmppmManganese: < 0.1Manganese: < 0.1 ppmppm



Total Suspended Solids (TSS): Total Suspended Solids (TSS): –– < 25< 25 ppmppm for film fillfor film fill

Total Dissolved Solids (TDS): Total Dissolved Solids (TDS): –– < 5000< 5000 ppmppm for thermal performancefor thermal performance

Oil and Grease: Oil and Grease: –– Avoid with film fill (contributes to fill plugging, Avoid with film fill (contributes to fill plugging,

prevents proper seasoning).prevents proper seasoning).Ammonia: Ammonia: –– Limit to 50Limit to 50 ppmppm if copper alloys are presentif copper alloys are present



Combinations of treatment chemicals may Combinations of treatment chemicals may cause reactions which reduce treatment cause reactions which reduce treatment effectivenesseffectivenessCertain chemicals such as surfactants,Certain chemicals such as surfactants,biodispersantsbiodispersants and antifoams may increase and antifoams may increase drift ratedrift rateConsult CT & WT vendors/consultantsConsult CT & WT vendors/consultants


Concentrations and Concentrations and BlowdownBlowdown

Evaporating water leaves minerals, Evaporating water leaves minerals, concentrates over timeconcentrates over timeBlowdown Blowdown of a small amount of water of a small amount of water keeps concentration at desired levelkeeps concentration at desired levelC = (R x EPD + BD + D)/(BD + D)C = (R x EPD + BD + D)/(BD + D)



Example:Example:–– Evaporation = 0.08% circulating water per Evaporation = 0.08% circulating water per

degree of rangedegree of range–– Drift = 0.02% of circulating water rateDrift = 0.02% of circulating water rate–– Range = 10 Deg FRange = 10 Deg F–– Concentrations = 5Concentrations = 5–– Blowdown Blowdown = 0.18% of circulating water rate= 0.18% of circulating water rate



Range 1.5 2 2.5 3 4 5 65 0.78 0.36 0.23 0.21 0.11 0.08 0.0610 1.58 0.76 0.50 0.41 0.24 0.18 0.1415 2.38 1.16 0.77 0.61 0.37 0.28 0.2220 3.18 1.56 1.03 0.81 0.51 0.38 0.3025 3.98 1.96 1.30 1.01 0.64 0.48 0.3830 4.78 2.36 1.57 1.21 0.77 0.58 0.4635 5.58 2.76 1.83 1.41 0.91 0.68 0.54

Based on: 0.02 % drift rate and 0.08 % evaporation rate

Operation for System EfficiencyOperation for System Efficiency


Condensing Water TemperatureCondensing Water Temperature

•• 3 GPM/TR (95°/85°/78°)3 GPM/TR (95°/85°/78°)•• 2 GPM/TR (105°/85°/78°)2 GPM/TR (105°/85°/78°)•• Lower condensing Lower condensing

temperatures, fans full, temperatures, fans full, gives coldest water at gives coldest water at chillerchiller

•• Chiller energy savings Chiller energy savings almost always outweighs almost always outweighs tower fan energy tower fan energy consumptionconsumption

0.0350.04

0.0450.05

0.0550.06

0.0650.07

0.0750.08

0.085

80 81 82 83 84 85 86 87

3 GPM/TON 2 GPM/TON

DESIGN COLD WATER TEMP. — (°F)

HP

per

TON

DESIGN COOLING TOWER FAN HP VARIATIONFAN HP PER TON OF LOAD

(BASIS: 75°F WET-BULB)


Capacity Control MethodologiesCapacity Control Methodologies

•• Capacity Control DampersCapacity Control Dampers•• MultiMulti--speed Motorsspeed Motors•• Variable Frequency DrivesVariable Frequency Drives•• Single Speed Fan CyclingSingle Speed Fan Cycling•• Free CoolingFree Cooling•• Fans full Speed Fans full Speed –– Run Wild Run Wild


Capacity Control DampersCapacity Control Dampers

•• Offers precise system controlOffers precise system control•• No fan power savingsNo fan power savings


Effect of Fan Speed on CapacityEffect of Fan Speed on Capacity

0

20

40

60

80

100

0 10 20 30 40 50 60 70 80 90 100

CAPACITY (AIRFLOW) REQUIRED POWER

PERCENT OF DESIGN FAN SPEED

PERCENT

FAN CHARACTERISTICSCAPACITY & HORSEPOWER RELATIVE TO SPEED


Single Speed, Full PowerSingle Speed, Full Power

45505560657075808590

20 30 40 50 60 70 80

10°F RANGE

WET BULB TEMPERATURE — (°F)

COLD

WATER

TYPICAL COOLING TOWER PERFORMANCESINGLE CELL TOWER — SINGLE SPEED FAN


Two SpeedTwo Speed

45505560657075808590

20 30 40 50 60 70 80

FULL SPEED HALF SPEED


COLD

WATER

TYPICAL COOLING TOWER PERFORMANCESINGLE CELL TOWER — TWO SPEED FAN

(10°F RANGE)


Two Cell, Two SpeedTwo Cell, Two Speed

45505560657075808590

20 30 40 50 60 70 80

FULL SPEED 1 HALF, 1 FULL HALF SPEED


COLD

WATER

TYPICAL COOLING TOWER PERFORMANCETWO CELL TOWER — TWO SPEED FANS

(10°F RANGE)


Variable Variable FrequencyFrequency

35° 45° 55° 65° 75° 85°

80%

60%

40%

20%

0

90°

80°

Cold Water °F

100%

100%

Control Temperature

Variable FrequencyDrive Fan

Control


Compressor ImpactCompressor Impact

45505560657075808590

20 30 40 50 60 70 80

10°F RANGE


COLD

WATER


Region for influencing compressor horsepower.


Compressor PowerCompressor Power

8486889092949698

100

70 75 80 85

COMPRESSOR HORSEPOWER

COLD WATER TEMPERATURE (°F)

PERCENT

POTENTIAL COMPRESSOR HP REDUCTIONSCONSTANT LOAD — REDUCING CONDENSER WATER TEMPERATURE

This is a “rule of thumb” curve. Verify actual reductions with chiller manufacturer.


Free Cooling RegionFree Cooling Region

45505560657075808590

20 30 40 50 60 70 80

10°F RANGE


COLD

WATER


Region for consideration of “free cooling”.


“Free Cooling”“Free Cooling”••When the tower can produce sufficiently When the tower can produce sufficiently cold water without the chiller.cold water without the chiller.

••Direct free cooling..Direct free cooling..

••Indirect free cooling..Indirect free cooling..


Free Cooling OperationFree Cooling Operation

Graph assumes that the system will go to free cooling when the tower is capable of producing 50°F or colder water.

4045505560657075808590

20 30 40 50 60 70 80

CHILLER ON CHILLER OFF


COLD

WATER

TYPICAL COOLING TOWER PERFORMANCEFULL LOAD — FULL FAN SPEED — FULL WATER FLOW


Benefit Depends on LocationBenefit Depends on Location

0

2000

4000

6000

8000

10000

-10 0 10 20 30 40 50 60 70 80

ANNUAL HOURS INDICATED W.B. WILL NOT BE EXCEEDED


HOURS

WET BULB OCCURRANCEDES MOINES VICINITY


Cooling Tower Operation and Cooling Tower Operation and Maintenance for Improved Maintenance for Improved

Energy EfficiencyEnergy Efficiency