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temperatureand flow rateof the facility
supplywater. Sinceawater-to-water
heatexchangerhasanapproach
temperature, the facilitycoolingwater
will neverbe thesame temperatureas
theambient riveror lakewaterbeing
drawn from.
Anotherconsideration for riverand lake
sourcecooling is theneed toobtain
operatingpermits touse thewater. In
theUnitedStateseachstateand
localityhasaseparateprocessand
application that is reviewedby the
state-levelEnvironmentalProtection
Agency. Typical state regulationsallow
up toabout 1,000,000gallons
(3,785,000 liters)perdayper
application,which isabout694gallons
(2,627 liters)perminute, but this limit
canbeoftenbeexceeded forcooling-
onlyapplicationsandwheredischarge
water temperature isnotexpected to
be relativelyhigh.Other typical
limitations for riverusemaybe that the
water temperaturedoesnotexceed
90˚F (32.2˚C)or that50%of the river
flowcannotbe increasedby5˚F
(2.8˚C).
Lastlyare theconcerns forpotential
flooding, drought, orother
uncontrollableweatherconditions.
Thesemay impact thesiteperformance
but the riskscanbemitigatedwith
properplanningandpreparing for such
extremesbydesigning tostrenuous
circumstances thata riveror lakemay
face.
LAKESOURCECOOLING
SYSTEMS
Lakesareoftensoughtafterasa
preferredcoolingsourceover rivers
since they tend tohaveastable
temperaturedependingon the
location, depth, andother factors that
canbeanticipated. Lakes tend tohave
a relativelyconstant temperaturebased
upon thedepth, asdeeper lakesdonot
have thermoclines that shift
dramaticallyorbecomeunstablewith
the turbulenceof springandautumn
changes. Figure 1 shows theaverage
temperatures fora lakedependingon
thedepth.
A lakedepthmustbesufficient foran
even, low temperature tobeexpected
year-round. Thesizeofa lakealsoplays
a role, asadeep lakeofanarrowwidth
maybesusceptible toseveremixing in
the fall andspringaswell asduring
stormsandother intenseweather
conditions.AsFigure 1belowshows, a
minimumdepthofabout40 to50 feet
(12.2 to 15.2meters) isnecessary to
reachastable temperatureofabout
39.2˚F (4˚C).
Cornell Lake SourceCoolingProject
In2000CornellUniversitybegan touse
a lakesourcesystem thatutilizedan
average temperatureof39˚F (3.9˚C)
from thebottomofCayugaLakenear
Ithica,NY. Thesystemsupportspeak
coolingacross thecampusofabout
16,000 tons. Thecold lakewater is
circulated throughheatexchangersata
facilityat theshoreviaasingle56 inch
(1.42meter)diameterHighDensity
Polyethylene (HDPE)pipe.Ascreen
covers the intake toprevent fishand
otherorganisms fromentering the
openendedpipeat thebottomof the
lake, approximately250 feet (76.2
meters)below thesurface.Anoutflow
pipe returns thewarmerwateratabout
56˚F (13.3˚C)atadepthof
approximately 12 feet (3.7meters)
below thesurfaceof the lake. This is
similar to theoutflow fromseveral
wastewater treatmentplants located
nearby. SeeFigure2below fora
schematicof thesystem.
Since itscompletion in2000, the
Cornell LakeSourceCoolingProject
presentsacompletedprojectwitha
recordofconsistentcoolingwater
direct froma lakesource. Theproject
allowed for the removalofchillersand
cooling towersatmanyof itsbuildings,
vastly reducing thespace, energycost,
andmaintenance requirementswithin
thosebuildings.
CriticalFacilitiesApplication:
Aswith
mostdeepwater lakes, thecooling
temperature iswellwithin the
acceptable range fora typicaldata
center.Oneof the largestconcerns fora
missioncritical system is redundancy;
theCornell LakeSourceCoolingProject
hasasingle intakepipe thatwouldbe
seenasasinglepointof failure riskby
datacentercustomers thatwouldneed
tobeaddressed. This levelof risk is
unacceptable formostmissioncritical
facilities, sobackupsystemoralternate
pipingconfigurationmustbe installed.
EnwaveEnergyCorporationDeep
LakeWaterCooling
TheEnwaveEnergyCorporation
providesdowntownToronto,Canada
withyear-roundcoolingviaadeep lake
watercoolingsystem. Three intake
pipespullwater fromLakeOntarioata
depthof272 feet (83meters)where the
water isaconstant39.2˚F (4˚C). The
water is filteredand treatedata
filtrationplant foruseaspotablewater
beforebeingpumped to theenergy
transfer station.Heatexchangers
transferheat from thecity’sclosed loop
chilledwater system to thecold lake
water. The lakewatercontinuesonas
potablewater to thecitywhile the
closed loopchilledwatercannowcool
over30downtownbuildingsvia
customerheatexchangers. Sinceeach
customerhasadedicatedheat
exchanger, theyareonlycharged for
theamountofcooling thateach
buildinguses. The three intakepipes
from the lakeareeach3.1miles (5km)
longandanother7.5miles (12km)of
chilledwaterpiping looparound the
city todistributecooling.
There isno returnpiping to the lakeas
allof thewater isused tosupport the
city’spotablewater supply. This
presentedanopportunity tocoordinate
withaseparateutility tomake themost
outofwhat isbeingextracted from the
lake. Tosupport thesystem incaseof
lowpotablewaterdemandorother
issueswith the lakewater source, there
Figure1:Thermoclines fora typical lake inNorthAmericawith temperature gradients
are shown for summerandwinter conditions.
Figure2:Pictorial cross sectiondiagramof theCornell Lake
SourceCoolingProject.
