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Cooling:Best Practices and Economizers
Cooling:Best Practices and Economizers
1
Randall Poet
A C Systems
Server Load = CRAC Capacity Server Airflow = CRAC Airflow
2
Ideal Situation
The Conventional Approach – Base CaseRaise the Return / Supply Air TempContain the Cold Aisle Add Intelligent ControlThe Set-upSummary
3
Agenda
Hot aisle / Cold aisle Blanking panels in racks Blanking panels between racks Blanking Panels between racks and floor Cable cut-outs covered Relatively clean underfloor area Proper location of CRAC units Vapor barrier around space
4
Start with Best Practices
20 Racks◦ 8 kW each◦ 35F delta T
5
Base Case – 75F Return Air Control 4 CRACs (N+1)
54 kW each 21F delta T design
20 Racks◦ 8 kW each◦ 35F delta T
6
Base Case – 75F Return Air Control 3 CRACs
Running 54 kW each 21F delta T design
Unit Airflow – 24,000 CFM Rack Airflow – 14,600 CFM Bypass Airflow – 9,400 CFM
7
Base Case Operating Scenario
75F
89F
54F
54F
CFM 100%
8
The Airflow Pattern
9
Typical Air Cooled DXEnergy Consumption
Evap Fan MotorCompressors
Condenser Fan Motors
Compressors run at full capacity Fans run at full speed
10
Typical Energy Consumption
Evap Fan MotorCompressors
Condenser Fan Motors
System kW 75F RA
Compressors 35.4
Evap Fans 8.7
Condenser Fans
5.4
Total 49.5
The Conventional Approach – Base CaseRaise the Return / Supply Air TempContain the Cold Aisle Add Intelligent ControlThe Set-upSummary
11
Agenda
Unit Airflow – 24,000 CFM Rack Airflow – 14,600 CFM Bypass Airflow – 9,400 CFM
12
New Operating Scenario85F
99F
64F
64F
CFM 100%
13
Increased Capacity at Full Airflow
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Increased Capacity at Full Airflow
Compressors run at reduced capacity or unloaded Fan motors run at full speed
15
Operating Systems Comparison
System kW 75F RA 85F RA
Compressors 35.4 24.9
Evap Fans 8.7 8.7
Condenser Fans 5.4 5.4
Total 49.5 39.0
Base 78.8%
Sanity Check –100 dF OAT, 6400’ ASL
16
Sanity Check
17
The Conventional Approach – Base CaseRaise the Return / Supply Air TempContain the Cold Aisle Add Intelligent ControlThe Set-upSummary
18
Agenda
Unit Airflow – 21,600 CFM Rack Airflow – 15,800 CFM Bypass Airflow – 5,800 CFM
19
Contain the Cold Aisle85F
94F
62F
62F
CFM 90%
At the higher RA temperature, the contained system has very similar operating costs as the non-contained
Fan motors run at full speed but at a reduced CFM and HP due to the higher static pressure
Compressors run at reduced capacity or unloaded but slightly higher than the non-contained
20
Operating Systems ComparisonSystem kW 75F RA 85F RA 85F RA
Contained
Compressors 35.4 24.9 25.8
Evap Fans 8.7 8.7 7.5
Condenser Fans
5.4 5.4 5.4
Total 49.5 39.0 38.7
Base 78.8% 78.2%
21
Why use Containment??
System operating costs are similarContainment partitions and doors cost $$
22
Hot Spots in Racks due toWrap-Around
23
No Leakage into the Cold AIsle
24
Higher Temperatures without Containment
25
Containment of Cold Aisle
Issues to Consider Fire Detection / Suppression
◦ Wide variation between municipalities◦ If local Fire Inspector involved early, typically goes
well Curtains usually eliminate this issue
Installation◦ Will be site specificy
Irregular row length/height, gaps, etc.◦ Site conditions critical, one size does NOT fit all
Issues To Consider ADA
◦ CAC space is for Service Personnel (Section 4.1.1) What about cooling for components in rest
of room?◦ Best solution today may be ducted return from hot
aisle◦ Perf tiles near other equipment requiring cooling
(eg. UPS) 85⁰ Room temperature?
HAC vs CAC Main Purpose of Cooling in Data Center?
◦ Cool the equipment Data Centers commonly on raised floor
◦ CAC allows current investment to be used HAC typically requires in row cooling
◦ So, refrigerant or chilled water and condensate intermingled with IT equipment and racks
Which aisle does majority of work take place in?◦ CAC hot aisle likely in 85⁰F range
Can use perf tiles in other space◦ HAC hot aisle likely in 100⁰F range
The Conventional Approach – Base CaseRaise the Return / Supply Air TempContain the Cold Aisle Add Intelligent ControlThe Set-upSummary
29
Agenda
Unit Airflow – 16,800 CFM Rack Airflow – 14,600 CFM Bypass Airflow – 2,200 CFM
30
Closer to Matching the Load to the Cooling
92F
97F
62F
62F
CFM 70%
Variable Capacity Compressors
Variable Speed Fans Intelligent Control
The airflows and capacities/loads are more closely matched
Fan motors run at reduced speed, CFM and HP based on the demand in the contained area
Compressors run at reduced capacity or unloaded but slightly higher than the non-contained
31
Operating Systems ComparisonSystem kW 75F RA 85F RA 85F RA
Contained92F RA Contained
& Controlled
Compressors 35.4 24.9 25.8 25.5
Evap Fans 8.7 8.7 7.5 3.0
Condenser Fans 5.4 5.4 5.4 5.4
Total 49.5 39.0 38.7 33.9
Base 78.8% 78.2% 68.5%
The Conventional Approach – Base CaseRaise the Return / Supply Air TempContain the Cold Aisle Add Intelligent Control (Creating SmartAisle)The Set-upSummary
32
Agenda
33
Sensor Location• Server centric solution, meaning that it focuses on the inlet
temperature to the servers• Self adapting to environment changes due to server utilization,
equipment location changes and outside variables• Can adapt to situations with no containment, end containment, and
full containment
Rack Sensors• Rack Sensors without doors
can be mounted on the frame of the racks.
• Temperature differences were within .5°F
Cold Aisle Sensors• Sensors can also be mounted at the top
of cold aisles when rack mounting is unavailable
36
Supply Compensation
• Compensation is the magical link between controlling sensors• The controller evaluates the Rack Sensors and Fan Speed• If the fan is operating at 100% and remains above the cold
aisle set point• Then the supply temperature set point will slowly lower to
drive the correct cold aisle temperature
Lower Supply
Fan Speed100%
CW Valve Open %
100%90%80%70%60%50%40%30%20%10%0%
Fan Speed %
Controller and CRAC Operation
Incre
ase in
kW
Unit ON
IT Load IncreasesRack Temperature Sensor detects inlet rack temperature
Fan Speed IncreasesSo that cold aisle temperature is maintained at customer temperature Setpoint
Supply TemperatureThe increase in fan speed will result in a warmer supply air temperature which is detected by the supply air sensor that will increase cooling to maintain supply air setpoint
Cold Aisle ContainmentiCOM will automatically adjust to changes that result in a temperature increase or decrease
38
Controller and CRAC Operation• Advanced freeze protection routine
• Allow all units to reduce fan speed to 60%• Fan speed and compressor capacity (or CW valve) managed for
best unit efficiency and performance• Multiple remote sensors
• Controller can use averaged and maximum/minimum values to individually control multiple CRAC systems
• CRAC systems work as a team• All remote sensors used• Increase capacity of other applicable adjacent units if one is at
maximum and unable to handle the load• Automatically adjust for units not in service
The Conventional Approach – Base CaseRaise the Return / Supply Air TempContain the Cold Aisle Add Intelligent ControlThe Set-upSummary
39
Agenda
Issues to Consider Fire Detection / Suppression
◦ Wide variation between municipalities◦ If local Fire Inspector involved early, typically goes
well Curtain eliminates this issue
Installation◦ Will be a local responsibility◦ You need to develop relationship with local Cable
Contractor or similar company for installation Irregular row length/height
◦ Site Survey critical◦ Most expensive component
Issues To Consider ADA
◦ Consultant raised issue at BAIS project◦ Successfully defended CAC space is for Service
Personnel (Section 4.1.1) What about cooling for components in rest
of room?◦ Best solution today is ducted return from hot aisle◦ perf tile by IT component
85⁰ Room temperature
Issues To Consider Purpose of Cooling in Data Center?
◦ Control equipment inlet temps Data Centers often on raised floor
◦ CAC allows current investment to be used Which aisle does majority of work take place
in?◦ CAC hot aisle likely in 85⁰F range
Could use perf tile in other space◦ HAC hot aisle likely in 100⁰F range
Best practices are a must if improved efficiency is a goal
Running warmer temperatures in the space will improve the cooling system operating efficiency
Containment improves the availability of the servers by eliminating hot spots
Intelligently controlling fan speed and compressor capacity “balances” the system to operate at it’s most efficient level
43
Summary
Summary Efficiency is the story, not containment Containment can be done in several ways,
none necessarily fit all situations Each critical space is unique and merits
individual planning Dynamic Control is (currently )the final
element
…Shifting on to Economizers and Equipment Considerations…
45
90.1 Economizer Map
Definitions of Cooling Efficiency EER (Energy Efficiency Ratio)
◦ Total Cooling Capacity (BTUH)/Total power input (watts)
◦ Full-load value on 95F design day◦ Commercial return air conditions of 80F/50%
SCOP (Sensible Coefficient of Performance)◦ Sensible Cooling Capacity (kW)/Total power input
(kW)◦ Full-load value on 95F design day◦ Data Center return air conditions of 75F/45%
47
ASCOP – Efficiency MetricAnnualized Sensible Coefficient of
Performance(location specific)
Bin efficiency x bin hours/total annual hours Factors hours at each efficiency operating
point Factors part-load efficiency Factors economizer hours
48
Single System –Outside Air Economizer
49
Large or Multiple Systems –Outside Air Economizer
50
Single System withGlycol Economizer
51
Precooler on Chilled Water System
52
Chilled Water withCooling Tower Economizer
53
What if we could do a refrigerant based economizer cycle?
54
Energy Consuming ComponentsAir-Cooled System
55
Compressor energy reduction is low-hanging fruit
Digital Scroll Technology Continuous variable capacity
compressor technology without inverter drive from 10% to 100% of capacity
In commercial use since 2004 Available in single compressor
and tandem compressor configurations
High reliability versus Inverter drive systems
No electrical harmonics introduced
56
EC fans in unit
57
EC fans in raised floor
58
EconoPhase Pumped Refrigerant Economizer
59
Condenser
Check Valve
Compressors ON
EvaporatorElectronic expansion
valve
Summer operation
Check Valve
Check Valve
Refrigerant
Pumps OFF
SolenoidValve
EconoPhase
Outdoor Ambient 95°F
KW @ 70% Load 24.1
Circuit 2
Circuit 1
EconoPhase – Partial Economization
60
Condenser
Check Valve
Compressor
EvaporatorElectronic expansion
valve
Fall / Evening operation
Check Valve
Check Valve
Refrigerant
Pump
SolenoidValve
EconoPhase
Outdoor Ambient 65°F
KW @ 70% Load 15.1
Circuit 2
Circuit 1
ON
OFF
OFF
ON
EconoPhase - Full Economization
61
Condenser
Check Valve
Compressor
EvaporatorElectronic expansion valve
Winter operation
Check Valve
Check Valve
Refrigerant
Pump
SolenoidValve
EconoPhase
Outdoor Ambient 25°F
KW @ 70% Load 3.7
Circuit 2
Circuit 1
ON
OFF
ON
OFF
Technology
Electronic Expansion Valve EC Plug FansTandem compressors w/ Digital Scroll New Evaporator Coil design
◦ Staged “A” Coil◦ Greater surface area
Microchannel Condenser◦ Indoor Unit Communicates to Condenser
Refrigerant Economizer
Advantages ofRefrigerant Economizer
No additional heat exchangers No dust or contamination concerns No need for added ductwork or structural
changes to building for economizer No dampers to maintain Quick changeover between compressor
mode and economizer mode No water usage No water freeze or coil freeze concerns
63
45F 55F 65F 75F 85F 95F1.8
2.3
2.8
3.3
3.8
4.3
4.8
5.3
5.8
6.3
6.8
Outdoor Ambient, F
Eff
icie
ncy
, S
CO
PLiebert DSE Full-Load Efficiency SCOP (kW/kW) @ 85F return air
Liebert DSE DA125A @ 50% load
ASHRAE 90.1 @ 75F
Efficiency Plateau
+92%
Liebert DSE DA125A @ 100%
load
+45%
+115%
Traditional Refrigeration
With Refrigerant Economizer Maximum capacity, max airflow
65
0 10 20 30 40 50 600
2
4
6
8
10
12
14
16
0
20
40
60
80
100
120
140
SC
OP
, kW
/kW
Se
ns
ible
kW
= Sensible Capacity, kW
= SCOP
Ambient, ºF
Designing for LEED
Energy efficiencyNo water use for coolingMERV 13 filtersNo outside air contaminationR-410A refrigerant/lower charge
Utility Rebates
66
Condenser Improvements
67
Air Cooled Condenser Improvements
Microchannel vs. Fin and Tube Variable Speed Fans Control Based on Refrigerant Pressure
68
Aluminum Fins & Tubes Developed & used in Automotive A/C for
25+yrs
69
Microchannel Coil
70
Microchannel Coil Advantage
1” Thin coil replaces 2” to 6” fin/tube coil◦ Lower airside ∆P◦ Reduced maximum fan wattage for heat transfer◦ Reduced refirgerant quantity
6”1”
EC Axial Fan Technology EC (Electronically Commutated) Motor
◦ Every fan/motor is designed for variable speed. Superior part load efficiency
◦ 3-Phase AC power feed, but efficiency of a DC motor
◦ 20% reduction of fan speed = 49% savings in energy
71
Sound Quiet fan blade design
72
Sound Level Factors & Options
Sound varies with fan speed Fan speed is proportional to % compressor
load and outdoor ambient temperature◦ Will you ever hear a lightly loaded system
condenser? Even more quiet options
◦ Upsizing condenser will keep fan speed in nearly “inaudible” range!
73
Why do they cool things with air, anyway??
74
75
Why indeed? How about pumped refrigerant?
Refrigerant piping anifold suppliespumped refrigerant
Cam levers activates engagement and disengagement of server
Refrigerant connection points at top of the rack on left side. All plumbing runs along left side.
Cooling Architecture
Each server is cooled by an individual cold plate◦ Cold plates and insertion mechanism is designed for use of standard 1U
servers Circulating refrigerant is the cooling medium
Rack
Server
Heat exchanger &
circulation unit
Cold PlateTo/From Chiller
Cold Plate Highly flexible Backed with pressure
plate Forms to the server lid
In-Rack Cooling withPumped Refrigerant
The rack is 45U tall by 800mm wide by 1200mm deep.
36 1U server slots with cold plate Three non-cooled server slots for
“cool” devices like switches, etc. Can be configured for a cooling
capacity of 20kW or 40kW.
78
Thank You.Questions?