optimizing cooling towers

8/4/2019 Optimizing Cooling Towers

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ucing energy costs fm your

!ling tower may be asas regular maintenance.Technology Update will ex-how proper maintenance willd help your equipment op-

1. Hot water from chiller. Flow control valve. Distribution nonelsDrift eliminators5. Make-u water infeed

7. Collection basin. Strainer. Cooled water to chiller10. Fan11.Gear box12. Drive shaft13. Fan drive14. Bleed water

. Float vave

OptimizingTower PerformanceIt's not unusual or the water in an mproperly maintained coolingtower to be 5 to 10"Fwarmer than the water in a properly maintainedcooling tower. Your chiller could consume up to 3.5percent moreenergy for each degree hotter the return (cold) water of the coolingtower becomes.If, for example, your cooling system uses $50,000 of electricity per year,it would cost you an additional$1,750 per year for every 1"F rise incooling water temperature.This means that if your cooling water tem-perature operates5 to 10?Fwarmer you could expect to pay an addi-tional $8,750 to $17,500 a year for electricity.Let's look at another example. If you operate a 100kW chiller 4,000hours per year and pay $0.05 per kWh, it will cost you an additional$700.00 per year for every degree cooling water temperature rises. Ifyour cooling water temperature operates5 o IO "Fwarmer you canexpect to pay an additional $3,500 to $7,000 a year.

EfficientOperationCooling towers found in industry, schools, office buildings, hospitals,and other commercial buildings are usually "open loop" systems.Inone application, water is circulated around condensing tubes of a chillerwhere it picks up heat. The warm water is then broken into small dropsby spraying it over the "fill" in the cooling tower (see Figure 1).Air isblown through the fill where it picks up heat from the water. Directheat transferred to the air accounts for only about 25 percent of the heatremoved from the water. The remaining 75 percent of the heat is re-moved as the water is evaporated. The cooled water is then collected inWater is constantly being added to the system because so much water isremoved by evaporation. When water evaporates from the cooling

the tower basin where it is recirculated through the system.

FA X 1-800-872-3882 Electronic Bulletin Board 1-800-782-3319. - - - -- -- .ADMINISTRATION


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PROBLEM CAUSE EFFECT SOLUTIONScale deposits form on Evaporation and water The amount of heat Measure the waterthe surface of the fill, treatment are problems. transferred from the treatment chemicalpipes, and nozzles. water to the air is residual in the circulationI . reduced. Operation water and maintain theefficiency is reduced residual recommendedand q u i ment lifeis by your water treatmentshortens. specialist.Spray nozzles are clogged. Algae and sediment are Cooling tower water is Maintain proper watermitted to collect in the hotter and its flow treatment chemicalKin. through the fill is residual. Clean thereduced. strainer on the bottom ofthe basin regularly.Water and air flow Spray nozzles are clogged. Water temperature in the Remove sediment fromthrough the fill is uneven. cooling tower is hotterthan necessary. strainer regularly.the basin and clean

tower it leaves scale deposits onthe surfaceof the fill from miner-als that were dissolved in thewater. These deposits are com-posed mostly of calaum, iron,and silica. Allowing the scale tobuild up on the fill surfaceofclosed circuit cooling towers re-duces the amount of heat trans-ferred from the water to the air.Excessive scale build-up on anopen cooling tower may indicateinadequate water treatment.

Algae and sediment, permittedto collect in the basin, will inter-fere with water circulationanddrastically reduce cooling towerperformance. Clogged spraynozzles will cause uneven waterdistribution and affect air flow.More air will flow through thedry section of the fi l l because ofreduced resistance and rob airfrom the wet parts. Table 1 s alist of common problems,causes, effects, and solutions tocooling tower performance.

MaintenanceA properly maintained coolingtower will keep your equipmentoperating more efficiently andsave you money. Schedule yourmaintenance regularly and keepa record of allmaintenance per-formed (Table2).


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Collect and test a water sampleusing the kit provided by yourwater treatment consultant.,Measure he cycles ofconcentrationof the waterflowin6 through the tower.Maintain the proper concen-tration of dissolved solids byadjusting the bleed water flow.easure the water treatmentchemical residual in the cir-culation water. Maintain theresidual recommended by yourwater treatment specialist.

heck the strainer on the bottomof the basin and clean it ifnecessary.Operate the make u p water floatswitch manually to ensureproper operation.Inspect all moving parts, such asdrive shafts, pulleys, and belts.Check for excessive vibration inmotors and pumps.

ook for oil leaks in gear boxes.Test the vibration limit switchbypur$sely jarrin8 it.h$d heSWI ch for corrosion tha couldprevent it from o r t i n gproperly.Never lsconnect thevibration limit switch. If it cuts offoften,ook for the source ofvibration.

heck for structural deterioration,looseconnectors,water leaks, andopenings in the casing.During periods of cold weather,check wnterization equipment.Make sure any ice accumulationis within acceptable levels.

PERIOD CCheck the distribution spraynozzles to ensure evendistribution over the fill.Check the distribution basin forcorrosion, leaks, and sediment.Operate flow control valvesthrough their range of travel andreset for even water flowthrough the fill.Remove any sludge from thecollection basin and check forcorrosion that could develop intoleaks.

HCheck the drift eliminators, airintake louvers, and fill for scalebuild-up. Clean louvers and drifteliminators with high-pressurewash. The fill may require acidcleaning.HLook for dama ed orout-of-place filH lements.Ins ctmotor supports, fanblag.s,and other mechanicalparts for excessive ware or cracks.

HCheck the level of oil in the gearbox. Add oil asneeded.HLubricate bearings and bushings.HAdjust belts and pulleys.

!FMake sure there is proclearance between the an bladesand the shroud. Move theshroud or fan as required.HCheck the amount of verticallay in the gear box output shaft&y pulling u on the tip of the

back and forward to determinethe amount of free rotation onthe drive shaft. If movement ineither shaft seem excessive, call aqualified cooling tower servicecontractor.

fan blades. 1p rn the drive shaft

ANNUALHCheck the casing, basin, andi ing for corrosion and decay.u h o u t proper maintenancecooling towersmay suffer fromcorrosion and wood decayWelded repairs are especiallysusceptible to corrosion. Primeand paint any welded repairswith a corrosion-resistantcoating. The rotective Zinc

towers is burned off during thewelding process.coating on g3 anized steel

HLeaks in the cooling tower casingmay allow air to bypass the fill.All cracks, holes, ga s, and doorsealed.access panels shoul$be properlyRemove dust, scale, and algaefrom the fill, basin, anddistribution spray nozzles tomaintain proper water flow.


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IiV Electric Ideas Clearinghouse is acomprehensive in@ sourcefm commercial and industrialen-ergy users. It is operated by theWashington State E w g y Office

and is part o f the Electric Ideastechnology transfer program spon-sored by participating utilities andthe Bonneuille PowerAdministration.

V Neither the United States nor theBonneville Power Administration,the state o f Washington, the Wash-ington State E n e r g y O@e, norany o f their contractors, subcon-tractors,or their employees makeany mrran ty, expressed or im-plied, or assume any legal responsi-bility for the accuracy,completeness,or usefulness of anyinformation, apparatus, prcduct,orprocess disclosed within thepublication.

V Technology Update CH-12V Toll-free Hotline:1-800-8 72-3568

Fax: 1-800-872-3882Electronic Bulletin Board:1-800-762-3319

BibliographyAir-conditioning and Refrigeration Institute.xefvigeration andAir-Conditioning. Prentice-Hall. pp. 133-137.1987.Burns,R. Cooling Towers, The Neglected Energy Resource.Republishedin Retrofit Opportunities For Energy Management andCogeneration. pp.47-53. The Associationof Energy Engineers. Compiledand edited by F.W. Payne. Prentice-Hall. 1989.Graves, P. Understanding Air Conditioning Systems For BetterEnergy Efficiency Prepared for the Illinois Dept. of Energy, ILENR/BE-87/01.1987.IrisCommunications, Inc.Keeping up with cooling towers, romBuilding Operator, Number 4. Tualatin, Oregon. November 1990.McQuiston, F.C. and J.D.Parker. Heating, Ventilating, n d AirConditioning Analysis and Design. John Wiley& Sons, Inc.Trane Corporation. Air Conditioning Training Manual. 1965.pp.537-547.1988.

DOVBP-39833-34June 199215 C

optimizing cooling towers

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