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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
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 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
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