Data Center Airflow:A Predictive Model

Roger R. Schmidtc28rrs@us.ibm.com

Chief Thermal Architect, IBM Corporation

Suhas V. Patankarpatankar@inres.com

President, Innovative Research, Inc.

Agenda

• Product Heat Load Trends• Data Center/Equipment Cooling• Data Center Flow Measurements• Data Center Predictive Model/

Comparison with Measurements

Microprocessor Power Trends

1995 2000 2005 2010 2015Year

60

80

100

120

140

160

180

200

Max

imum

chi

p po

wer

(W) 1994 NTRS 1997 NTRS 1999 ITRS

26 - 43 W/cm2

30 - 88 W/cm2

Consortium of Computer and Telecom ManufacturersWill be published by Site Uptime Group

• Amdahl • Compaq• Cisco • Cray • Dell • HP

• IBM • Lucent • Nortel • Sun • Unisys

Heat Load Trends

Data Processing/Telecom Equipment Heat Load Trends

Year of Announcement1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

Hea

t Loa

d pe

r Mac

hine

/Equ

ipm

ent A

rea

- wat

ts/ft

2

6080

200

400

600800

2000

4000

60008000

100

1000

10000

Hea

t Loa

d pe

r Mac

hine

/Equ

ipm

ent A

rea

- wat

ts/m

2

800

2000

4000

60008000

20000

40000

6000080000

1000

10000

100000

TapesWorkstationsServers & DASD(tall racks)

Communication Equipment(Frames)

Projections for Heat Loads

The Site Uptime Group

IBM’s xSeries Servers

1 frame7.7 sq. ft. 7.6 kW max Max 982 watts/ft2

1800 lbs(133 lbs/sq.ft.)

Environmental Facts

IBM’s zSeries Servers

1 or 2 frames14.4 sq. ft. for 1 fr.7.6 kW max for 1 fr.Max 527 watts/ft2

60 Amp dual power plugs2621 lbs(121 lbs/ft2)

Environmental Facts

Product Family Heat Density Trend Chart

Year of Product First Shipment1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

Hea

t Loa

d pe

r Pro

duct

Foo

tprin

t - w

atts

/ft2 -fo

otpr

int

6080

200

400

600800

2000

4000

60008000

100

1000

10000

Hea

t Loa

d pe

r Pro

duct

Foo

tprin

t - w

atts

/m2 -fo

otpr

int

800

2000

4000

60008000

20000

40000

6000080000

1000

10000

100000

CommunicationEquipment(Frames)

Workstations(standalone)

Tape Storage SystemsServers & Disk Storage Systems (1.8-2.2m tall)

xx

The Site Uptime Group

zSeries Cluster

8 tiles

16 tiles

527 watts/ft2

based on systemfootprint

263 watts/ft2

based on minimumsystem service clearances

Typical Functional Allocation within Data Center

Electrically active IT hardware - 30%Service Clearances around products - 30%Site infrastructure support equipment - 20%Main aisles and other inactive areas - 20%

Complete Data Center

0.30 x 527 watts/ft2 = 158 watts/ft2

Partially Configured Systems(Ave. of 50% total load) 0.50 x 158 watts/ft2=79 watts/ft2

Agenda

• Product Heat Load Trends• Data Center/Equipment Cooling• Data Center Flow Measurements• Data Center Predictive Model/

Comparison with Measurements

CRAC CRAC

Servers/Storage

Servers/Storage

Servers/Storage

Servers/Storage

Subfloor

Raised Floor

Computer Data Center Cooling

Perforated Floor Tiles (6, 11, 25, 40, 60% open)

Data Center Cooling

Data Center Characteristics

Raised Floor

Sub floor

zSeries

EPO Panel

dT

cfm

Power Dissipated P

dT = fcn(cfm,P)

Perforated Floor Tile

Objective: Maintain EPO panel thermistors below 35C

Chiller Air Flowrate Required for zSeries

Area of Floor Tiles to SupplyChilled Air to Freeway System

zSeries

Other Computer Systems

Centerline ofAisle Walkway

29.5" to 32.6"

65.4"

(depends on whether side covers are installed)

Rear

Front

Chilled Air Flow Requirements

Underfloor Air Temperature(C)8 10 12 14 16 18 20 22 24 26

Air F

low

Rat

e(cf

m) f

or c

ross

-hat

ched

are

a

200

400

600

800

1000

1200

1400

1600

4.0 kW

6.5 kW

9.0 kW

Agenda

• Product Heat Load Trends• Data Center/Equipment Cooling• Data Center Flow Measurements• Data Center Predictive Model/

Comparison with Measurements

Data Center Floor Plan - Test Area

30'

26'

L

L

Current Flow Test Area

66'

20'

CRAC Units

Test Area Perforated Tile Test CasesA

B

AB

AB

4 x

15 ti

les

2 x

15 ti

les

AB

1 x

10 ti

les

1 x

10 ti

les

1 x

10 ti

les

2 x 7 tiles

Case 1 Case 2 Case 3 Case 4

2 x 7 tiles

2 x 7 tiles

2 x 7 tiles

AB

4 x

15 ti

les

4 x

4 ti

les

Case 5

1 x 7 tiles

Calibrated Flow Tool

Boxed-In Test Area

“25%” Open Floor Tile

Data Center Test - Case 1

AB

4 x

15 ti

les

1 2 3 4 5 6 7 8 9 10 1112 1314 15

Tile Row no.

-300

-100

100

300

Air F

low

rate

(cfm

)

Flow Distribution - Test #10

Data Center Test - Case 4

Wes

t 1W

est 2

Wes

t 3W

est 4

Wes

t 5W

est 6

Wes

t 7W

est 8

Wes

t 9W

est 1

0W

est 1

1W

est 1

2C

hille

r 1 2 3 4 5 6 7 8 910 11 12 13 14 15

Tile Row no.

-200-100

0100200300400500

Air F

low

rate

(cfm

)

AB

2 x 7 tiles2 x 7 tiles

2 x 7 tiles

2 x 7 tiles

1 x 7 tiles

Data Center Test - Case 5

Wes

t 1W

est 2

Wes

t 3W

est 4

Wes

t 5W

est 6

Wes

t 7W

est 8

Wes

t 9W

est 1

0W

est 1

1W

est 1

2C

hille

r 1 2 3 4 5 6 7 8 910 11 12 13 14 15

Tile row no.

-200-100

0100200300400500

Air F

low

rate

(cfm

)

AB

1 x

10 ti

les

1 x

10 ti

les

1 x

10 ti

les

Agenda

• Product Heat Load Trends• Data Center/Equipment Cooling• Data Center Flow Measurements• Data Center Predictive Model/

Comparison with Measurements

Objectives of the Model

• Calculation of airflow distribution through the floor tiles for the whole data center

• Ability to vary chiller flow, tile perforations, and raised-floor height

• Easy-to-use, fast, flexible• Intended for routine use by data-center

designers and operators

Basis of the Model

• A two-dimensional (depth-averaged) calculation of the velocity and pressure fields under the raised floor is performed.

• The chiller flow is specified as inflow.• The outflow through the perforated tiles is

calculated from:∆p = A Q2

where ∆p is the pressure drop andQ is the volumetric flow rate

The Cause of Flow Maldistribution

Results of the Model

Comparison With Measurements

Comparison With Measurements

Comparison With Measurements

Comparison With Measurements

Flow Maldistribution Revisited

Effect of Tile Open Area

Effect of Plenum Height

Industry Needs

• Heat loads of Data Processing Equipment are increasing.

• Sufficient chilled airflow must be supplied to maintain high reliability.

• Complex layouts of systems, chillers, and perforated tiles present extra challenges.

• A validated predictive tool is needed to aid in balancing/optimizing airflow distribution throughout the data center.

Our Contribution

• Detailed airflow measurements have been conducted on a data center with a variety of chiller and tile arrangements.

• A computational model has been developed for the prediction of the flow through the perforated tiles.

• The model predictions give good agreement with the measurements.

• One run of the model requires 1-2 minutes on a 300MHz Pentium computer.