8/13/2019 Water Cooled Air Cooled Comparison

1/3

Tower

Pump/Tank

Condenser

1

2

7

46

5

1Evaporator Evaporator

ACCondenser

Compressors

8

3 RefrigerantPiping

WaterCooledvs AirCooledChiller

1.Compressorenergycost

2.Makeupwatercosts

3.Sewer

charges

4.Chemicalcosts

5.Towerprocesspump

6.Towerpump

7.Towerfan

8.Aircooledcondenserfans

AirCooledvs.WaterCooledChillersOperatingCosts

Conventionalthinkinghasbeenthatwatercooledchillersaremoreefficientthanaircooledchillers. Ifweonlylookatcompressor

costs,thismaybetrue. However,usingstateofthearttechnologywithcentrifugalcompressorsandvariablespeedcontrol,air

cooledchillersareoftenthebetterchoice

8/13/2019 Water Cooled Air Cooled Comparison

2/3

Total

OperatingCosts

1.Compressor

2.MakeUpWater

7.TowerFan

5./6.Tower

Pumps

8.Condenser

Fans

3.Sewer

Charges

4.

Chemicals

8/13/2019 Water Cooled Air Cooled Comparison

3/3

System System Operating Operating TotalUnit TotalChiller

Loading Cooling Profile Time Energy EnergyCost

(%) Load (%) (Hrs/Yr) Consumption ($/Yr)(Tons) (kW/Ton)

100% 140 1% 60 0.614 $361

75% 105 42% 2,520 0.591 $10,940

50% 70 45% 2,700 0.619 $8,192

25% 35 12% 720 0.619 $1,092

100% $20,585

Coolingtowersystemwatercost(evaporation) $4,699

Coolingtowersystemwatercost(bleedoff) $940

Coolingtowersystemchemcialtreatmentcost $2,268

Coolingtowersystempumpenergy(process&

recirculationpumps) $8,428

Coolingtower

system

cooling

tower

fan

energy

cost $1,094

Coolingtoweroperatingcosttotal $17,429

Typicalcoolingtowerannualoperatingcost $17,429

TypicalR134Awatercooledrotaryscrewchillerannual

energycost $20,585

Totalfor

Typical

R

134A

water

cooled

rotary

screw

compressor $38,014

TypicalR134Awatercooledrotaryscrewchillerannual

operatingcost $38,014

ThermalCareR134Aaircooledcentrifugalchiller

annualoperatingcost ($15,828)

58%totalannual

savings $22,186

Itisimportanttolookatthetotaloperatingcostsinvolved

withthechillers,notjustthecompressorcosts. Asthe

graphicindicates,coolingtoweroperatingcostsshouldbe

addedtotheoperatingcostsofawatercooledchiller. A

coolingtowersystem'scostsincludethetowerfan,water

andsewer

costs,

chemical

costs

and

pumping

costs. In

processapplications,towersystemsgenerallyhaveprocess

pumpsandrecirculationpumpswhichcanaddasignificant

cost. Theillustrationbelowcomparestheoperatingcostof

anaircooledvariablespeedcentrifugalchillerversusa

watercooledscrewchiller. Thiscomparisonisbasedupon

a140

ton

load,

Chicago

weather

data,

$.07/kwh electrical

costs,$5.00/1000gallonwaterandsewercostsand6,000

hrs/yearoperation.

Becausetheaircooledchillerusesfloatingheadpressure

control,thecompressorenergycostsareactuallylessthan

thewatercooledchiller'scompressorcostsa$4,757

difference($20,585

$15,585). Adding

the

tower

system's

operatingcostof$17,429resultsina$22,186/year

operatingcostsavings. Amoreefficientvariablespeed

watercooledcentrifugalchillerreducesthecostdifference

to$16,725stillasignificantannualcostpenalty.