economizers for data centers - cfroundtable.org center 8.2 • • • • central chilled water...
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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