Economizers for Data CentersPeter Rumsey, P.E.

Energy Consumption in Typical Data Center

Servers and Data

Equipment55%

HVAC (Fans, Compressors,

etc.)30%

Lighting3%

Other12%

Some Definitions

Air Side EconomizersThe use of outside air directly supplied to the space for cooling purposes

Water Side EconomizersThe use of cooling tower water to provide chilled water to a chilled water cooling systemIsolated from chilled water loop with heat exchangerAlso known as “free cooling”

Air Side Economizers

San Jose, CAWYE Psychrometric Chart

RH = 20%

RH =

60%

RH

= 80

%

h = 30 Btu/lb ⎯⎯→

h = 40 Btu/lb ⎯⎯→

h = 50 Btu/lb ⎯⎯→

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0140

0.0160

0.0180

0.0200

0.0220

0.0240

0.0260

0.0280

0.0300

30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120

Dry Bulb Temperature (F)

Hum

idity

Rat

io (l

bs H

2O p

er lb

s dr

y ai

r)Air-Side EconomizeToa<55 100% Econ – 3140 hrs/yrToa>55 and Toa<70 partial Econ. – 4096 hrs

LBNLData Center Benchmarking Case Study

HVAC Power Consumption

29%31%

25%

50%

36%

31% 32%

54%

22%

46%

35%

1 2 3 4.1 4.5 5 6.2 7 8.1 8.2 9

Facility No. - Data Center No.

All values are shown as a fraction of the respective data center total power consumption.

Worst Case "HVAC Efficiency"

Best Case "HVAC Efficiency"

California Energy Commission and NYSERDA Data Center Benchmarking

CRAC Units Versus

Air Handlers

How did they do it?

Data Center 8.1• Air cooled CRAC units• No economizing• Constant Speed Fans• Humidification control• All CRAC units on

Data Center 8.2••

••

Central chilled water plantCentral air handling units with VFDs and ECONOMIZERSMinimal humidity controlData Monitoring – Gateways, EMCS

City of Oakland Data Center

House Air System Air Side Economizer

and Chilled Water System

VFD

Cold Aisle

Cold Aisle

Hot Aisle

Hot Aisle

Hot Aisle

DX Package Unit For use on nights and weekends

Economizer Capable

BD

Results

Doubled Cooling CapacityAllowed for the removal of several portable coolers

Annual Energy Savings$20,000 per year

Humidification on low humidity days with electric humidifier

Analyses for other facilities – New Construction

Data Center Size

Annual Energy Saved (kWh)

Annual Energy

Cost Saved

Savings by Design

Incentive

Estimated Cost to

Implement

Estimated Simple

Payback (years)

30,600 SF 498,000 $69,800 $10,500 $21,000 0.2

9,600 SF 200,000 $28,000 $7,500* $15,000 0.3

THE HUMIDITY ISSUE

San Jose, CAWYE Psychrometric Chart

RH = 20%

RH =

60%

RH

= 80

%

h = 30 Btu/lb ⎯⎯→

h = 40 Btu/lb ⎯⎯→

h = 50 Btu/lb ⎯⎯→

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0140

0.0160

0.0180

0.0200

0.0220

0.0240

0.0260

0.0280

0.0300

30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120

Dry Bulb Temperature (F)

Hum

idity

Rat

io (l

bs H

2O p

er lb

s dr

y ai

r)

Dewpoint < 38 Deg F and Tdb <70 deg FHumidify 1200 Hours Per Year

Comparison of Economizer versus Compressor Cooling

Cooling Costs – Air Cooled CRACs or Chillers (1.2 kW/ton)100% recirculation - $3.26/cfm/yrEconomizer in San Jose - $1.65/cfm/yr49% savings

Cooling Costs – Water Cooled Chiller (system 0.8 kW/ton)100% recirculation - $2.17/cfm/yrEconomizer in San Jose - $1.22/cfm/yr43% savings

Includes additional costs of humidification with electric humidifier up to 30% RH at 70 deg F - $0.36/cfm/yr

Water Side Economizers

Free Cooling

Water Side Economizer In Series with Chilled Water

M

M

M

CHW Return 65 Deg F

CHW 60 Deg F

CHW Supply 50 Deg F

Chiller #2

Chiller #1

CHW Supply 50 Deg F

CWS

CWS

CWR

CWR

San Jose, CAWYE Psychrometric Chart

RH = 20%

RH =

60%

RH

= 80

%

h = 30 Btu/lb ⎯⎯→

h = 40 Btu/lb ⎯⎯→

h = 50 Btu/lb ⎯⎯→

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0140

0.0160

0.0180

0.0200

0.0220

0.0240

0.0260

0.0280

0.0300

30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120

Dry Bulb Temperature (F)

Hum

idity

Rat

io (l

bs H

2O p

er lb

s dr

y ai

r)

Free Cooling / WaterSide EconomizeIf Chilled Water Supply Temperature is 50 deg F…Twb<40 100% Econ – 570 hrs/yrTwb>40 and Twb<55 partial Econ. – 4610 hrs/yr

Twb=40 deg F

Twb=55 deg F

Another way to look at it….

0.1 to 0.2 kW/tonWater Side Economizer0 - ? kW/tonAir Side Economizer0.5 – 0.8 kW/tonWater Cooled Chiller - System1.2-1.4 kW/tonAir Cooled Chiller - System1.2-1.4 kW/tonAir Cooled CRAC Efficiency

Thank you