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2
Electronic Cooling Solutions Inc.
• Thermal management consulting company
• Located in the heart of Silicon Valley
• Provide solutions for thermal design problems
• Use of experience, modeling & experimental methods in the design process
• Clients include over 60 companies
3
Outline
• Introduction
• Need for Innovative Cooling Solutions
• Objective
• Scope of this Presentation
• Cooling Solutions – Air-based Cooling Systems
– Water-based Cooling Systems
– Refrigerant-based Cooling Systems
• Comparative Analysis
• Conclusion
• Vendor Contacts
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Introduction - Power Density and Heat Load Trends• Electrical Power = Waste Heat
• Increase in power densities from the CPU-level to the System-level
Component level
Board-level System-level Rack-level Room-level
• Current power density at the rack level = 1 to 3 kilowatts (up to 30 kilowatts per rack in two to four years - Hannemann and Chu ‘07)
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Need for Innovative Cooling Solutions at Rack-Level• Datacenter TCO is characterized on a per rack basis
• Addition of newer and higher powered equipment in existing datacenters
• Hotspots in datacenter resulting from high-density servers
• Hotspots resulting from unavailability of cooling air from CRAC units
• Design shortcomings within the rack result in inefficient cooling
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Objective
• Cooling of equipment in rack using airflow and impact of minor design changes for better cooling
• Cooling of high density equipment using water-based cooling techniques
• Cooling of high density equipment using refrigeration-based cooling techniques
• Provide vendor data for the above mentioned products
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Scope of this Presentation
• Limited to discussion of cooling solutions only at the rack level
• Closed racks and commercially available products
• Discussion on Component-level, Board-level and Room-level cooling can be personally consulted
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Airflow-based Cooling Techniques
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Cooling of Racks with Conditioned Air
• Most easy to implement and maintain
• Limitation based on cooling capacity, acoustics and power consumption
• Detailed analysis could improve efficiency of air cooling
Application of Computational Fluid Dynamics (CFD)• Pressure drops and airflow patterns
• Determine by-pass air
• Determine areas of re-circulation
• Determine failure modes of cabinet fans
• Requires testing to develop confidence in models
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Cooling of Racks with Conditioned Air
Airflow Enhancement in Racks
• Based on CFD Analysis
• Sample case study 1
• Sample case study 2
• Cabinet powered fans – airflow layouts
• Best practices
• Airflow enhancing products
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Sample Case Study 1
• Study done by Electronic Cooling Solutions Inc.,
• 42U Cabinet fitted with twenty one 2U units
• 15.75 kilowatts per rack
• Inlet temperature of 40 deg C
• Airflow – 1932 CFM
• 10,000 ft Altitude Conditions
• Simplified cabinet shown here
• Objective was to optimize the cabinet for better cooling/use of higher powered equipment
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Sample Case Study 1 (Contd …)
Inlet Temperature
Higher temperatures at the inlet sides
Re-circulation of Flow
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Sample Case Study 1 (Contd …)• Added vertical blockages
Vertical blockages between the rack rails and cabinet sides
Open space between the rack rails and cabinet sides
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Sample Case Study 1 (Contd …)
• Added blockage above the topmost unit of the rack
Area above the topmost 2U rack is
blocked
Top of 2U server
Top of rack cover meant for passing
cables from front to rear
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Sample Case Study 1 (Contd …)
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Sample Case Study 1 (Contd …)
Comparison of Inlet
Temperatures
No blockages Blocked passages
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Sample Case Study 1 (Contd …)
Fixed Exhaust Temperature (deg C) 55 60
No
BlockagesWith
BlockagesNo
BlockagesWith
Blockages
Mean Inlet Temperature (deg C) 43.9 41.2 43.9 41.2
Fixed Airflow 92 CFM
Power (W) per unit 397 493 575 675
Total power of Rack (kW) 8.3 10.3 12.1 14.1• Current study shows 17 to 25 % increase in power dissipation based on exhaust temperature.
• By blocking re-circulating flow, it is possible to use higher powered equipment in the rack.
• Blocking can be done by employing Brush Strips.
• Avoid using larger racks with rails set to lower rack width settings (Using 23” rack with rails set to hold 19” equipment)
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Sample Case Study 2
• Study done by Electronic Cooling Solutions Inc.,
• Racks placed in containers
• Create airflow model of blowers
• Evaluate alternate designs for blower module
Symmetry Walls
Container wall
Heat Exchanger
2U Servers
2U Servers
Blower Module
Rack Model
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Sample Case Study 2
• Apprx 20% increase in airflow with the re-designed baffles and perforated casing
Module 1 – 860 CFM
Testing
Testing to collect data for modeling
Module 2 – 1024 CFM
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Cooling of Racks with Conditioned Air
Airflow Enhancement in Racks
• Based on CFD Analysis
• Sample case study 1
• Sample case study 2
• Cabinet powered fans – airflow layouts
• Best practices
• Airflow enhancing products
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Airflow Enhancers – Cabinet Powered Fans
Supply Air
Raised Floor
Front In – Rear Out
Supply Air
Ceiling
Raised Floor
Front In – Top Out
Front or Footprint Inlet
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Airflow Enhancers (Cabinet Best Practices)
Supply Air
Raised Floor
Supply Air
Raised Floor
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Airflow Enhancers (Cabinet Best Practices (Contd…))
Supply Air
Raised Floor
Dropped Ceiling
Supply Air
Raised Floor
Dropped Ceiling
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Airflow Enhancing Products•APC 2U Rack Air Distribution
•Delivers air directly from the raised floor into the rack inlet
•Minimizes top-bottom inlet temperature distribution
•Allows rack loads up to 3.5 kilowatts per rack
Side Rack Air Distribution Unit
Application View
Bottom-Top Rack Air Distribution Unit
Roof Air Removal Unit
Images: APC (www.apc.com)
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Airflow Enhancing Products (Contd…)
•Higher density rear door rack air removal unit
•Allows rack loads up to 16.5 kilowatts /14 kilowatts per rack
•Challenges in obtaining flow through tiles in the datacenter
Rittal Enclosure BlowerRittal Side Breathing Air
Baffle System
APC Liebert XDA
Images: Rittal (www.rittal-corp.com)
Images: www.apc.com and www.liebert.com
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Water-based Cooling Techniques
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Water-based Cooling
• Basis: QLOAD = mCp DT = rVCp DT
(Water has 3000 times higher heat carrying capacity than air)
• Chilled water from building supply
• Cooling high density servers up to 70 kilowatts per rack
• Lower energy cost as some of the CRAC units can be removed
• Avoid hotspots due to high power-density equipment
• Possible to have redundant systems (Chillers, pumps, piping, and power supply) to avoid downtime
• Importance of CDU
• Electrically conductive, corrosiveness and high flow rates
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Water-based Cooling
Raised Floor Raised Floor
Combination of Air and Water Cooling
Pure Water-based CoolingH
eat
Exch
anger
Heat Exchanger
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Water-based Cooling• Cooling system design by Naissus Thermal Management Solutions
• Heat removal of 20+ kilowatts
• Closed liquid loop with bottom mounted fin and tube heat exchanger
•Thermal test done with 5 blade serversPerformance Table - North American units SI units
Inputs Heat Load 24.0 kW 24.0 kW
Water Temp 12.8 degC 12.8 degC
Water Flow 0.76 l/sec 0.76 l/sec
Results Cold Air Supply 22.8 degC 22.8 degC
Hot Air Disch 49.8 degC 49.8 degC
Air DT 27.0 degC 27.0 degC
Water Rise 7.1 degC 7.1 degC
Water Disch 19.9 degC 19.9 degC
Water P.D. 48.3 kPa 48.3 kPa
Background Server Fans 1680 CFM Varies by manufacturer
Fan Power 700 watts
Performance Table - North American units SI units
Inputs Heat Load 24.0 kW 24.0 kW
Water Temp 12.8 degC 12.8 degC
Water Flow 0.76 l/sec 0.76 l/sec
Results Cold Air Supply 22.8 degC 22.8 degC
Hot Air Disch 49.8 degC 49.8 degC
Air DT 27.0 degC 27.0 degC
Water Rise 7.1 degC 7.1 degC
Water Disch 19.9 degC 19.9 degC
Water P.D. 48.3 kPa 48.3 kPa
Background Server Fans 1680 CFM Varies by manufacturer
Fan Power 700 watts
Heated Air
Thermal Core
Water from ChillerWater sent to Chiller
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Water-based Cooling
Temperature Distribution inside the Rack
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Water-based Cooling•Cooling system design by Vette Corp.
•Heat removal of up to 30 kilowatts
•Rear door closed loop liquid heat exchanger designed by IBM
•Currently available only for IBM Enterprise Rack
•Available from Rittal for retro-fit designs
IBM Rear Door Heat Exchanger
Pressure drop across the heat exchanger for a typical 1U fan setup
Images: www.vette-corp.com
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Water-based Cooling
•Cooling system design by APC.
•Heat removal of up to 70 kilowatts
•Controlled in-row cooling
•Row air containment
•Modularity
•Similar designs from HP (35 kilowatts)
•Similar concepts available from Rittal (30 kilowatts)
•Similar concepts available from Liebert (8 kilowatts and 17 kilowatts)
Heat Exchanger and Fan Assembly
Front View Rear View
Images: www.apc.com
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Refrigerant-based Cooling Techniques
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Refrigerant-based Cooling
•Phase change (latent heat transfer)
•Electronics-safe
•Low flow rates and non-corrosive
•Some systems are stand-alone and hence flexible
•CRAC units are the most common ones
•Chilled water from building supply may be used for supplemental cooling
•Expensive ( comparable to water+ additives)
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Refrigerant-based Cooling•Cooling system design by Liebert
•XDF- Cooling capacity of 14 kilowatts
•Stand-alone unit
Liebert XDF Self Contained Unit Images: www.liebert.com
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Refrigerant-based Cooling
•Cooling system design by APC.
•Heat removal of up to 43 kilowatts
•Modularity
•Rack air containment
APC In-Row Cooling
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Refrigerant-based Cooling•Cooling system design by Liebert
•XDV- Rack mount air conditioners (10 kilowatts) - Almost no floor space required
•XDH-Rack Cooling capacity up to 30 kilowatts
•Also available from Rittal
Liebert Roof Mount Cooling Liebert In-Row Cooling Rittal Rear Door Hx
Images: www.liebert.com
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Liquid Based Touch Cooling
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Water/Refrigerant-based Touch Cooling
•Direct contact cooling combined with chip cooling
•Remove heat at the source
Available from:
Clustered Systems
Rittal (Power electronics)
SprayCool (20 to 30KW)
Cold plate with Liquid Cooling
Liquid Cooling of Boards
Spray CoolingImages: www.spraycool.com
Images: www.rittal-corp.com Images: www.ibm.com
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•Cooling system design by Thermal Form and Function
•Pumped liquid multiphase cooling
•Heat removal of up to 10 kilowatts
per evaporator (Modular)
•Designed for retro-fit applications
•Air/Water cooled condenser unit can be used
Thermal Form and Function Refrigeration Unit
Two Phase Flow
Images: http://www.thermalformandfunction.com/
Refrigerant-based Touch Cooling
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Comparison of Cooling Techniques
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Comparative Analysis
• Study by Hannemann and Chu – Interpack ’07
• Comparative study of cooling technologies with a model datacenter
Area required for Cooling Equipment Power Consumption of Cooling Equipment
Capital Expenditure of Cooling Equipment
43
Conclusion
• Reviewed innovative and commercially available technologies for cooling racks
• Discussed design approaches with use of CFD to maximize performance of air cooling
• Reviewed products and techniques for enhancing airflow within a rack
• Reviewed cooling of high density equipment using chilled water and refrigerant
• Selection of cooling strategy will depend on the specific requirements of the client
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Vendor Contacts
• APC – Morrison, Harold Wells Associates (925-355-9900)
• Rittal – Sales (800-477-4000)
• Liebert – Frank Stone (925-734-8660)
• Spray Cool – Sales (866-993-2665)
• Clustered Systems – Phil Hughes (415-613-9264)
• Trox AITCS - Thomas Hudgens (347-325-4347)
• Thermal Form and Function – Joe Marsala (978-526-9672)
• Vette Corp - Skye Emerson (508-203-4694)
• Naissus Thermal Management Solutions - Mirko Stevanovic (416-892-4071)
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References
• Product websites and communication with vendors
• Hannemann, R and Chu, H., (2007), “Analysis of Alternative Data Center Cooling Approaches”, ASME Interpack 1176, Vancouver, BC.
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Acknowledgement
• Speck Design
• Our colleagues at Electronic Cooling Solutions:
Khyati Varma
Ceferino Sanchez
Adriana Romero
Sridevi Iyengar
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