Saving Water in Cooling Tower SystemsSaving Water in Cooling Tower Systems

Technologies and TrendsTechnologies and Trends

Water Efficiency: Driving Sustainable Water Efficiency: Driving Sustainable Buildings and SitesBuildings and Sites

Sept 17, 2008Sept 17, 2008 Seattle, WASeattle, WA

Golden Gardens BathhouseGolden Gardens Bathhouse8498 8498 SeaviewSeaview Place NW, SeattlePlace NW, Seattle

Saving Water in Cooling Tower SystemsSaving Water in Cooling Tower Systems

A BASIC INTRODUCTIONA BASIC INTRODUCTION••Why Cooling Towers Why Cooling Towers

••Cooling Towers/Fluid CoolersCooling Towers/Fluid Coolers

••Water TreatmentWater Treatment

••MaintenanceMaintenance

••Hybrid SystemsHybrid Systems

WHY COOLING TOWERSWHY COOLING TOWERS

EfficiencyEfficiency

–– WetWet--Bulb Depression Allows Bulb Depression Allows Lower Condensing TemperaturesLower Condensing Temperatures

–– Cooling Towers are Water Saving Cooling Towers are Water Saving DevicesDevices

WATER SAVINGS TECHNOLOGYWATER SAVINGS TECHNOLOGY

Advantage: Latent Cooling vs. Advantage: Latent Cooling vs. Sensible Heat TransferSensible Heat Transfer

–– Sensible: 1 BTU/lb per degree F.Sensible: 1 BTU/lb per degree F.–– Latent: 1,000 BTU/lbLatent: 1,000 BTU/lb

(Heat of Vaporization)(Heat of Vaporization)

WHY LOOK FOR MORE SAVINGS?WHY LOOK FOR MORE SAVINGS?

Big user of waterBig user of waterTreatment chemicals:Treatment chemicals:

Carried out in driftCarried out in driftEmitted as Chlorine GasEmitted as Chlorine GasAffect Waste Water TreatmentAffect Waste Water Treatment

Impacts of Tower Chemical UseImpacts of Tower Chemical Use

OPEN SYSTEMSOPEN SYSTEMS

HOT WATER INHOT WATER IN

COLD WATER OUTCOLD WATER OUT

AIR INAIR IN AIR INAIR IN

HOT SATURATED DISCHARGE AIRHOT SATURATED DISCHARGE AIR

Hot Water Hot Water Distribution Distribution

SystemSystem

Fill MaterialFill MaterialAir Inlet Air Inlet LouversLouvers

Drift Drift EliminatorsEliminators

BasinBasin

INDUSTRIAL / HVAC COOLINGINDUSTRIAL / HVAC COOLING

OPEN LOOP

CLOSED LOOP

COOLING TOWER

CHILLER

AIR HANDLING UNIT

CHILLED WATER

PUMP

CONDENSER WATER

PUMP

CLOSED SYSTEMSCLOSED SYSTEMS

Cooled Water OutCooled Water Out

Hot Saturated Discharge AirHot Saturated Discharge Air

Hot Water InHot Water In

Cool DryCool DryEntering AirEntering Air

Fluid that services the system is contained and isolated Fluid that services the system is contained and isolated from the environment and spray water.from the environment and spray water.

CLOSED SYSTEMSCLOSED SYSTEMS

HeatHeatPumpPump

HeatHeatPumpPump

HeatHeatPumpPump

PumpPump

Fluid InFluid In

Fluid OutFluid Out

Closed circuit cooler serving heat pumps.Closed circuit cooler serving heat pumps.

COMPONENTSCOMPONENTS

–– Med. EfficiencyMed. Efficiency 0.005% = 63 0.005% = 63 Gal/DayGal/Day

= = 22,99522,995 GALLONS/YRGALLONS/YR–– High Efficiency 0.001% = 13 Gal/DayHigh Efficiency 0.001% = 13 Gal/Day

= 4,599 GALLONS/YR= 4,599 GALLONS/YR

Over 18,000 Gallons of Water & Water Over 18,000 Gallons of Water & Water Treatment Chemicals Every YearTreatment Chemicals Every Year

DRIFT ELIMINATORSDRIFT ELIMINATORS–– DRIFT RATES: EXAMPLEDRIFT RATES: EXAMPLE–– 500 TON COOLING TOWER AT NOMINAL 500 TON COOLING TOWER AT NOMINAL

CONDITIONS: 1,500 GPM , 14 HOURS/DAYCONDITIONS: 1,500 GPM , 14 HOURS/DAY

COMPONENTSCOMPONENTS

Replaceable, nonReplaceable, non--corrosive louvers.corrosive louvers.

Replaceable, nonReplaceable, non--corrosive eliminatorscorrosive eliminators

COMPONENTSCOMPONENTS

0.0030.003--5% drift rate5% drift rate

NonNon--ReplaceableReplaceable

Drift Eliminators Drift Eliminators –– Counterflow vs. CrossflowCounterflow vs. Crossflow

0.001% drift rate0.001% drift rate

ReplaceableReplaceable

COMPONENTSCOMPONENTS

NonNon--Corrosive / SS basin or PanelsCorrosive / SS basin or Panels–– Reduces Leaks Reduces Leaks

Sump SweeperSump Sweeper–– Reduces particulate buildup on basin and Reduces particulate buildup on basin and

therefore under deposit corrosion which therefore under deposit corrosion which can lead to leaks.can lead to leaks.

High Efficiency Splash LouversHigh Efficiency Splash Louvers–– SplashSplash--out is another path of water lossout is another path of water loss——

similar to drift, but usually less significant similar to drift, but usually less significant in a tower in good condition.in a tower in good condition.

WATER TREATMENTWATER TREATMENT

SCALINGSCALING

CORROSIONCORROSION

BIOLOGICAL GROWTHBIOLOGICAL GROWTH

WATER TREATMENTWATER TREATMENT

BLEED (BlowBLEED (Blow--Down)Down)Amount of Water Purposely Bled to Amount of Water Purposely Bled to Sewer.Sewer.

•• To Keep Levels of Impurity in To Keep Levels of Impurity in Recirc. Water Constant.Recirc. Water Constant.

WATER TREATMENTWATER TREATMENT

BLEED (BlowBLEED (Blow--Down)Down)As Water Evaporates, it Leaves As Water Evaporates, it Leaves Behind all of its Impurities. Behind all of its Impurities.

These will continue to build up, These will continue to build up, leading to corrosion, scaling, etc.leading to corrosion, scaling, etc.

WATER TREATMENTWATER TREATMENT

WATER TREATMENTWATER TREATMENTBLEED (BlowBLEED (Blow--Down)Down)

Bleed can be reduced by:Bleed can be reduced by:

Tower optionsTower options

Filtering Recirc. WaterFiltering Recirc. Water

Water TreatmentWater Treatment

Bleed can rarely be Bleed can rarely be completely eliminated.completely eliminated.

REDUCING BLEEDREDUCING BLEED

Tower Design StrategiesTower Design Strategies

Reduce Particulates, Debris and Sunlight Reduce Particulates, Debris and Sunlight

Enclosed spray headers (Debris, Sunlight)Enclosed spray headers (Debris, Sunlight)

Inlet Screens (Debris)Inlet Screens (Debris)

Enclosed Fill (Sunlight, Debris)Enclosed Fill (Sunlight, Debris)

SightSight--proof basins (Debris, Sunlight)proof basins (Debris, Sunlight)

Filter systems (Debris)Filter systems (Debris)

Sump Sweepers (Debris/Particulates)Sump Sweepers (Debris/Particulates)

REDUCING BLEEDREDUCING BLEED

Water Treatment StrategiesWater Treatment Strategies

Conductivity control of bleedConductivity control of bleed

Chemical corrosion and scale inhibitors, BiocidesChemical corrosion and scale inhibitors, Biocides

NonNon--Chemical methods of Treatment (pulsedChemical methods of Treatment (pulsed--power, power, cavitation, others).cavitation, others).

NonNon--Traditional methods of water treatment have Traditional methods of water treatment have recently shown great improvements in bleed recently shown great improvements in bleed reduction. Industry Studies (ASHRAE, CTI) have reduction. Industry Studies (ASHRAE, CTI) have supported some of these technologies. Caution supported some of these technologies. Caution should be exercised as many questionable should be exercised as many questionable technologies are on the market.technologies are on the market.

Frequent, Careful oversight essential!Frequent, Careful oversight essential!

Use dry finned coil to Use dry finned coil to reject as much heat as reject as much heat as possible, reducing possible, reducing needed evaporation needed evaporation but allowing low but allowing low condenser water condenser water temperatures available temperatures available with evap.with evap.

Water SavingsWater Savings

Hybrid SystemsHybrid Systems

Closed LoopClosed Loop--Tower Hybrid SystemTower Hybrid System

Hybrid Evaporative Condensing

88 F

DX

Coi

lDesuperheating Coil

Condensing Coil

Eliminators

Subcooling Coil

Evap Condenser Hybrid SystemEvap Condenser Hybrid System

OpenOpen--Tower Hybrid SystemTower Hybrid System

++

Precool condenser water before cooling towerPrecool condenser water before cooling tower

Hybrid Evaporative Cooler

Water Usage $7.8/kgal

Total Evaporation per year (kgal) 960 2,302

Total Sewer per year (kgal) 137 329

Total Water Make-up per year (kgal) 1,097 2,631

Total Water Cost per year ($) $8,557 $20,522

Energy/Power Usage $0.06/kWH

Fan energy (kW-Hr) 185,059 44,521

Spray Pump energy (kW-Hr) 17,181 20,637

Total Energy per year (kW-Hr) 202,240 65,158

Total Power Cost per year ($) $12,134 $3,909

Total Costs $20,691 $24,431

Cost SavingsCost Savings

WaterWater--Saving Hybrid Fluid CoolerSaving Hybrid Fluid Cooler

HYBRID SYSTEMSHYBRID SYSTEMS

Hybrid systems effectivelyreduce load at tower

Saving Water in Cooling Tower SystemsSaving Water in Cooling Tower Systems

SummarySummary••Cooling towers improve energy efficiency Cooling towers improve energy efficiency and reduce water use and reduce water use

••Water use driven by evaporation and bleedWater use driven by evaporation and bleed

••Water Treatment required to minimize bleedWater Treatment required to minimize bleed

••Maintenance is critical to preserve designed Maintenance is critical to preserve designed ––in water in water efficiecyefficiecy

••Hybrid Systems can greatly reduce water useHybrid Systems can greatly reduce water use