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7X24MAGAZINE SPRING2014
are two4,300 ton (15,100kW)chillers
atacentral coolingplant tosupport
customercoolingneeds.
CriticalFacilitiesApplication:
Thecold
water from thedepthsofLakeOntario
issuitable for theusewithadatacenter
as the largedepthminimizesany
changes to the inlet temperature.While
the lakesourcecooling that supports
Toronto,Canadahas three intakepipes
extending into the lake for redundancy,
theuseof thesystem isbasedon
potablewaterdemand insteadof
cooling load. Since therearealso
chillersavailable forcooling, themain
schematic for thiswouldbeaviable
option foradatacenter to take
advantageofdeep lakesourcecooling
whilekeeping the redundancyof
multiplechillers.
RIVERSOURCECOOLING
SYSTEMS
Unlike thedeeperwatersofa lake, the
temperatureofa riveratdepths
available forcoolingwater inletscan
varygreatlyover thecourseofayear.
Figure4aboveshowsa temperature
rangeandaverage temperaturesovera
typical year for thePotomacRivernear
Washington,DC. There isaconnection
between the temperatureand the river
depth,which isalsodependentupon
precipitation.
A riveralsovaries in temperaturewithin
hours, letalonedays. This issomewhat
similar tohowair temperatureschange
through thecourseofaday. Typicallya
cooling tower responds to these
changesaccordingly tosupply the
condenserwater temperatureneeded.
Similarly, a river sourcesystemwould
need toaccommodate thechanges in
the riverwater temperature.Abenefit
ofusing riverwaterasacoolingsource
in lieuofusingair for theheat sink is
that the temperaturechangesarenot
asdrastic inwateras forair,which
allows for smoother transitions from
freecooling tomechanical-supported
cooling, andback.
Anotherconsideration for river source
cooling is thedepthof the river. It is
necessary tostudy the temperature
trendsof the river tobeutilizedas the
coolingsource inorder to find the least
depthandhighest temperature to
anticipateworst-casescenariosand
apply reasonablesafetymargins. This
alsoapplies toconditionswhere the
riveroftensees freezingconditions that
maycomplicate intakeordischargeof
thewaterduring low flow, low load, or
othercritical conditions.
COMPARISONWITH
GUIDELINESFORLIQUID
COOLEDPROCESSING
ENVIRONMENTS
From theestablishedwhitepaper in
2011, “ThermalGuidelines forLiquid
CooledDataProcessingEnvironments”,
thereare five temperaturezones into
whichasystemcanbecategorized
basedon the liquidcooling
temperaturedirectlysupporting the IT
equipmentasshownonTable 1.
W1LiquidCoolingClass:
The facility
supplywater temperature range for the
W1classmaybe themost typical for
currentdatacenters. Theyarealso
traditionally fed fromacentralplant
withchillersandcooling towers to
rejectheat to theatmosphere.
Lakesourcecoolingmaypresent the
opportunity foreliminating this typeof
centralplant, similar to theCornell Lake
SourceCoolingProject.Year-round
temperaturesand redundancywould
need tobeaddressed, byeitherhaving
redundantpipesor standbyequipment.
River sourcecoolingwouldpresent
greaterchallenges. Thissolution isbest
suitedasa replacement forcooling
towersasameansofheat rejection
whilestill havingchillers toprovide
coolingwater to the facility.
W2LiquidCoolingClass:
TheW2class
mainandsupplemental cooling
equipment is typically thesameas the
W1classwithchillersandcooling
towers inacentralplant.Becauseof the
increased facilitysupplywater
temperature range, lakeand river
sourcecoolingoptionswouldbeeasier
to justify.A riverwatercoolingdesign
wouldstill havechallengesbasedon
Figure3:Lake source coolingdiagram forToronto,Canada courtesy
EnwaveEnergyCorporation.
Figure4:Measurement data from theU.S.Geological Survey shows the
water temperature of thePotomacRivernearWashington,DCas depicted
throughout 2013.Theblue line on the graph shows thewater temperature
1 foot above the riverbedover the last year.The yellowdots are the
correspondingwater temperaturemedians for the last five years.
