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DATA CENTER OPERATING

TEMPERATURE: WHATDOES DELL RECOMMEND?

By David MossDell Data Center Infrastructure

dell.com/hiddendatacenter

Thereislotsofhypethesedaysaboutoperatingyourdatacenterathighertemperatures.

Youmaybeaskingseveralquestionsregardingthistopic:

Howmuch

does

it

save

and

do

the

savings

outweigh

the

risks?

WhattemperatureshouldItarget?

Ihopetoanswertheriskquestioninsubsequentpapersdealingwithreliabilityimpacts

andridethroughtime. HavingparticipatedinbothGreenGridandtheASHRAEdata

comtechnicalgroup,thesearequestionswediscussatlength. ASHRAE,theAmerican

SocietyforHeating,Refrigeration,andAirConditioningEngineers,hasrecentlyincreased

itsrecommendedoperatingtemperaturesbyseveraldegrees. Atarecentmeeting,Iap

proachedanAPCcolleagueonthetopicofincreasedITtemperatures. Mytheorywas

thatalthoughanincreaseinITinlettemperaturesenablesenergysavingsinthecooling

process,itmightbethattheincreasedfanpowerassociatedwithhigherITinlettempera

turesmightnegatethefacilityefficiencyadvantages. Whatwefoundconfirmedmyhy

pothesis. Thereisasweetspotoperatingtemperaturewhenyouareusingmechanical

meansto

cool

your

data

center.

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DATA CENTER OPERATING TEMPERATURE: WHAT DOES DELL RECOMMEND?

DATA CENTERTEMPERATURE Airconditioningsystemsarecommonlycontrolledbymonitoringandmaintaining

aspecificreturnairtemperature. Whendiscussingtheroomtemperatureorset

point,youareusuallytalkingaboutthereturntemperature. ThisisNOTthetem

peraturethat

is

critical

for

IT

equipment.

The

only

temperature

the

IT

equipment

caresaboutistheinlettemperature,soinmostcasesyouaretalkingaboutapples

andoranges. Thispaperwillsuggestatemperatureinthemidtoupper70sas

beingidealforITequipmentwhenusingmechanicalcooling. Butifthistempera

tureisdescribingthereturnairtemperature,thesupplyairtemperatureentering

theITislikelyinthe50s. Thisisentirelytoocoldandisprobablythesingleworst

contributortotheinefficiencyofthedatacenter.

2JUNE 2009

THE HYPOTHESIS ITequipmentcanbereallyquiteefficientwithrespecttocoolingwhendelivered

lowtomoderatetemperatures. Designedtoaccommodatehottemperatures(95

degrees),internalfansspinfastandconsumelargeramountsofairtomaintain

acceptablecomponenttemperatures. Withamoderatetemperatureof,say75

degrees,thefansspindown,consumingarelativelysmallamountofairandfan

energy. 75degreesisgenerallythetemperaturewheretheITfanspeedsbottom

out. Withoutselectivelyturningsomefansoff,airconsumptionisusuallyaboutas

lowasitwillgoatthismoderatetemperature. TodaysDellservers,forinstance,

useabout10wattstopoweranentirefanbankatthistemperature. Butwhen

spinninguptoaccommodatehightemperatures,thefanpowercangrow510X.

Priortothisexperiment,thehypothesiswasthattherewasapointsomewhere

betweenthemoderate75degreeandthehigh95degreetemperaturewherethe

fanenergy

increase

might

be

greater

than

the

energy

saved

in

the

chilling

process.

Wesetouttotestthishypothesis.

Inacontrolledthermalchamber,energyandairflowconsumptionwasmeasured

forseveralactiveserversoverabroadrangeofinlettemperatures.

(from: EnergyImpactofIncreased ServerInletTemperature;DavidMoss,JohnH.Bean,Jr.,2009)

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DATA CENTER OPERATING TEMPERATURE: WHAT DOES DELL RECOMMEND?

3JUNE 2009

TheseservercharacteristicswerelaterrecreatedinanAPCtestfacilitycapableof

measuringfacilitypowerandcoolingenergyuse. APCsectionedaportionof

theirdatacentertestfacilitytoisolatethetestfromtheremainderoftheroom.

Theyessentially

built

alittle

room

within

the

lab.

Using

racked

simulator

units

to

producethepowerandflowcharacteristicsoftheservers,coolingwasadjusted

withinthetestroomtoprovidecoolingtotheservers. Chilledwaterandsup

plyairtemperatureswereadjustedtodeliverarangeofserverinlettempera

turessimilartotheservertestsrunatDell. Aswouldbeexpected,thefacility

coolingenergydecreasedwithincreasedoperatingtemperature. ButtheIT

powerstartstoincreaseatatemperatureinthemid70s. Whencombined,the

totalenergy,includingITandcooling,hitsaminimumbetween75and80de

grees.

Zoominginonthetotalcombinedrange,itisabiteasiertoseewherethesweet

spotfalls:

THE FACILITY TEST

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DATA CENTER OPERATING TEMPERATURE: WHAT DOES DELL RECOMMEND?

CONCLUSIONSWhenusingmechanicalmeanstocooladatacenter,thehighestoperatingtem

peraturemaynotbethemostefficient. Thispaperpointstoanexamplefacility

whereabove

acertain

temperature,

its

incremental

IT

power

increase

grew

faster

thanthedecreaseinenergyexpendedinthecoolingprocess. ASHRAErecently

adjustedtheiruppertemperaturerecommendationto27oC(80.6

oF). Thistem

peraturemaybeslightlyhigherthantheidealoperatingtemperaturesforsome

datacenters. Largeenergysavingsarepossible,primarilyinthechillingprocess,if

adatacenteradjustsitsoperatingtemperatureupward. Attentionshouldbepaid

toexistinghotspotsorequipmentnotcapableofrunningathighertemperatures

beforeattemptinganincreaseinoperatingtemperatures. Somedatacentersutil

izeeconomizerstosubstituteforthemechanicalcoolingprocess. Inthesefacili

ties,thetemperatureofminimumfacilityenergywouldbehigher.

4JUNE 2009

Formore

information,

please

consider

the

following

links:

EnergyAdvantagesofContainmentSystems:

http://content.dell.com/us/en/corp/d/business~solutions~whitepapers~en/

Documents~dcienergyadvantagesofcontainmentsystems.pdf.aspx

EnergyImpactofIncreasedServerInletTemperature:

http://content.dell.com/us/en/corp/d/business~solutions~whitepapers~en/

Documents~dcienergyimpactofincreasedinlettemp.pdf.aspx