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Full of Hot Air? Why a CFD Analysis Can Keep your Data Centre Cool


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Innovative data centres demand innovative cooling strategies. Predictive tools like Computational Fluid Dynamics (CFD) analysis can identify the origin of current and future thermal problems in data …

Innovative data centres demand innovative cooling strategies. Predictive tools like Computational Fluid Dynamics (CFD) analysis can identify the origin of current and future thermal problems in data centres. CFD maps, simulates and analyzes air flow, temperature and pressure to uncover hot spots, possible equipment malfunctions, physical layout challenges or other areas with potential cooling issues.

According to Gartner Research, data centres seldom meet the operational and capacity requirements of their initial design. Thermal issues are the most common data centre challenge; not mitigated, they can cause performance problems and system shutdowns.The thermal challenge in a data centre is to deliver the right amount of airflow at the right temperature to IT equipment while efficiently removing the heat generated. Lack of air flow, not temperature, is typically the cause of thermal issues. If the data centre is an existing facility, a high-level Thermal Assessment will help to identify current thermal management issues and degree of best practice adoption, but it won't provide an accurate assessment of future problems when additional IT equipment is deployed or changes are made to the data centre layout. Predictive simulation tools like Computational Fluid Dynamics (CFD) analysis can identify the origin of current and future thermal problems in data centres. CFD maps, simulates and analyzes air flow, temperature and pressure to uncover hot spots, possible equipment malfunctions, physical layout challenges or other areas with potential cooling issues.Join us as we discuss:ü Why high-density virtualised/consolidated environments demand a different and holistic approach to coolingü The most common cooling myths and why not to believe themü How several real world thermal cooling issues are solved with both traditional and advanced data centre containment solutions from the perspective of a Panduit corporate research engineerü How CFD thermal modeling solves complex cooling issues to reduce your cooling costs

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  • 1. Nick TaylorProfessional ServicesUPI Solutions Architect EMEA 10/31/2011
  • 2. 6Agenda – What is CFD? • 10 Cooling Myths • Illustrations of two Cooling Myths • Data Centre & ASHRAE Trends • CFD Design Inputs – Solving Cooling Dilemmas with CFD • Identifying Issues • Side-to-side Airflow Bypass Air = Wasted Cooling • Under Floor Airflow • Containment
  • 3. 8What is CFD?CFD = Computational Fluid Dynamics• Data Center simulation of air flow, temperature and pressure• Model created based on physical design and thermal characteristics of your Data CenterWhy do a CFD Analysis?• You can fix problems that you can not see• Engineer and Optimize new layout before it’s built• Breath additional life into your existing Data CenterHow can a CFD benefit my Data Center?• Identify root cause of cooling problems• Determine optimal solution before it’s implemented – eliminates trial and error• Save OpEx $ through cooling optimization strategies
  • 4. 910 Cooling Myths1) Hot spots are the problem2) Adding perforated tiles will solve the problem3) CFD only models raised floors4) Simulation of cabinet’s based on kW are adequate5) CFD modeling doesn’t require a trained CFD engineer6) Thermal Imaging cameras can identify cooling problems Cold Aisle Thermal Image shows7) Sealing raised floor cable openings doesn’t make a hot spot symptoms measureable difference and doesn’t need to be modeled8) Increasing set points and decreasing fan speeds can be optimized without a CFD9) Temperature sensors tell me where to deploy equipment10) Containment will solve the problem
  • 5. 10Illustration of Cooling Myth 4– Simulation of cabinet’s based on kW are adequate – Part 1 Server/Switch/Storage Manufacturer No Man’s Land Facilities Management
  • 6. 11Illustration of Cooling Myth 4– Simulation of cabinet’s based on kW are adequate – Part 2 ServersSame equipment, one works... one fails. Storage Switch
  • 7. 12Illustration of Cooling Myth 7- Sealing raised floor cable openings doesn’t make a bigdifference and therefore doesn’t need to be modeled Open Cable Cut Out Closed Cable Cut Outs Bypass Air & Recirculation Bypass Air eliminated by 166 CFM wasted per cutout sealing cable cut outs Assuming 5,000 sq. ft. DC with 150 No longer wasting $6,950 per year cabinets that’s 24,900 CFM wasted
  • 8. 13Data Center TrendsMore Computing = More Power• Per cabinet power load continues to climb – 6kW to 8kW is typical – 11kW to 15kW for high-density applications – 25kW+ is possible• High-power IT equipment has become the norm – 4kW blade servers – 12kW to 18kW switches – 11kW to 15kW storage arrays• Power density continues to skyrocket – 300 W/sq.ft. is the new standard and 500 W/sq.ft. is on the horizon
  • 9. 14ASHRAE Trends Over Time • 2011 Update: • 15-32c and 20% - 80% RH allowable for Class 1a equipment.• CFD can provide confidence in operating at higher temps.
  • 10. 15CFD Design Inputs and Correlation Data• Accurate CFD simulation begins with accurate and efficient data collection CRAC supply/return Identification of under Temp, Air Flow, & Humidity floor obstructions Identification of Future Equipment/Plenum Return Expansion PlansRoom Layout & Dimensions Equipment Inventory perLocation & Size cabinetof Cable/Power Openings 6 temp & AirflowTemp, Air Flow, per cabinet & Humidity at (Front & Back) end of rows Temp & Airflow Static Pressure per perf tile per row
  • 11. 16Thermal AssessmentAll CFD’s aren’t Created Equal Simple CFD Generic Under Floor Pressure Accurate CFD Detailed Under Floor Pressure Clearly Identifies Issues
  • 12. 17Solving Cooling Dilemmas with CFD • Identifying Issues • Side-to-side Airflow • Under-floor Airflow • Containment Example: Greenfield
  • 13. Solving Cooling Dilemmas with CFD• Create model of data center – Physical dimensions – HVAC system – Row layout and cabinets – IT Equipment – Underfloor or underfloor obstructions including cabling, pathways and pipework.• Solve model• Examine results and identify issues• Find root causes of issues• Improve design, update model• Repeat…….
  • 14. Data Center CFD Scenario – 56 Cabinets Total IT Load = 429.4 kW - Total IT Airflow = 81,082 CFMCFD Analysis of a Each Cabinet Each CabinetPlanned Data Center 8.2 kW 12 kW Empty 12 kW 2640 CFM 8.2 kW 987CFM 2640 CFM for growth 987CFM• 2850 sq. ft. room• Perimeter CRAC units with a 2’ raised floor• Supply Temp: 18°C• Cooling Airflow: 108,000 CFM 9.6 kW 9.6 kW• Airflow Ratio: 1.33 2600 CFM 3200 CFM• Range of 5-12kW per cabinet.• Average of 150W per sq.ft. 5.2kw 1091 CFM
  • 15. Temperature Profile 6ft. Above Floor 32.0c 28.5c 25.0c 21.5c 18.0c Temperature Profile 6ft. Above Floor
  • 16. Maximum Rack Inlet Temperatures 32.0c 28.5c 25.0c 21.5c 18.0c Max Inlet Air Temperatures
  • 17. First - Simple Best Practices – Add Sealing• No blanking panels in cabinet• Allows hot exhaust air to be drawn into server inlet 32.0c 28.5c 25.0c 21.5c 18.0c
  • 18. Improvements with Blanking Panels• Addition of blanking panels dramatically lowers maximum inlet temperatures• However, four switch cabinets remain hot Max Inlet Temperatures Without Sealing 32.0c 28.5c 25.0c 21.5c Max Inlet Temperatures With Sealing 18.0c
  • 19. Switches with Side-to Side-Airflow• Air inlet on right side• Exhaust on left side• Exhaust air simply circulates above and below switch back to inlet• Very little air drawn from cold aisle into cabinet Switch Cabinet Without Air Flow Ducting
  • 20. Add Ducting Solutions• Inlet duct added on right side as well as blanking panels• Ducting and blanking segregates hot and cold air• All inlet air now drawn from cold aisle Switch Cabinet With Air Flow Ducting
  • 21. Perforated Tile Air Flow• Next, evaluate supply of cold air to cabinets• Flow through perforated tiles ranges from 900 CFM to 1800 CFM• Why? Air Flow Through Perforated Tiles
  • 22. Under Floor Pressure and Tile Airflow Low Pressure Areas• Air flow is driven by pressure• Wide variation in pressure under floor• Tiles with low flow match areas of low pressure• Again, why? Under Floor Pressure (inches H20)
  • 23. Under Floor Pressure,Vortexs and Velocity• Vortexes have very low pressure at center• Static pressure decreases with increasing velocity (Bernoulli’s Principle) Under Floor Pressure Under Floor Velocities
  • 24. Air Flow Vortex • Vortexes often occur when – Perpendicular airflow intersect – Opposing airflows run adjacent to one another Vortex Under Floor Velocties
  • 25. Fixing Under Floor Issues• Move all CRAHS to be in line with hot aisles• Minimize airflow blockages - move cabling from under floor to over cabinet• Did this help? Under Floor Pressure
  • 26. Cabinet Inlet Temperatureswith Improved Tile Air Flow• Eliminated lower flow tiles in center of room• Only a small improvement in outside end of row tiles Perforated Tile Air Flow• Cabinet maximum inlet temperatures: 32.0c – Generally good 28.5c 25.0c – Slightly warmer at outside end 21.5c of row positions – 21.1°C to 18.0c 22.8°C – 27.6°F maximum inlet temperature at interior end of row (circled cabinets)• Why are the two end of row cabinets hot? Maximum Rack Inlet Temperatures
  • 27. End of Row Recirculation• Hot exhaust air can be be drawn around 32.0c 28.5c the cabinet to the rack 25.0c inlet 21.5c• Occurs despite good 18.0c airflow from perforated tiles• Recirculation can be seen to some degree at all end of rows without containment• So, how can this be Recirculation solved? Temperature Profile at 6 ft. Above Floor
  • 28. 32.0c 28.5cConsolidate Rows 25.0c 21.5c 18.0c• Slide rows together• Take advantage of higher under floor pressure in center of room• Eliminate gap between rows Maximum Rack Inlet Temperature• Cabinets physically block recirculation 32.0c• Max inlet now on end of row is 28.5c 21.5°C 25.0c 21.5c 18.0c Temperature Profile at 6 ft. Above Floor
  • 29. Cold Aisle Containment• Build a structure that physically separates air in the cold aisle from the rest of the room• Completely eliminates mixing of hot and cold air• With no recirculation: – Supply temperature can be raised – CRAC volumetric airflow can be lowered – Results in lower energy usage – decreases OpEX costs
  • 30. Cold AisleContainment Results• Room airflow decreased by 20% to 87,750 CFM• Airflow ratio is 1.08• Very uniform rack inlet temperature – no recirculation Maximum Rack Inlet Temperature• Can also safely raise supply air temperature by +3°C• Energy savings – Fan energy a function of the cube of fan speed – 20% decrease in fan speed can be a 50% decrease in fan energy – Raising supply temperature can save 3 to 6% for every 1 degree Centigrade Temperature Profile at 6 ft. Above Floor
  • 31. Vertical Exhaust Systems(Chimneys)• Solid rear doors and a veritical exhaust duct are install on each cabinet• Completely contains hot air and directs it back to a drop ceiling return plenum• Similar benefits to Cold Aisle Containment plus: – Entire room is a cool uniform temperature – Larger pool of reserve cool air in the event of a cooling failure – Supports slab floor (i.e. no raised floor required for cold air supply)
  • 32. 32.0c 28.5c 25.0c 21.5cChimney Cabinet 18.0cResults• Room airflow again set to 87,750 CFM, 20% below previous cases• Airflow ratio is 1.08• Entire data center at cool, Maximum Rack Inlet Temperature uniform temperature 32.0c 28.5c• Again, supply air temperature 25.0c 21.5c can be increased by +3°C 18.0c• Same energy savings as cold aisle containment Temperature Profile at 6 ft. Above Floor
  • 33. Benefits of a Well-Conducted CFD Analysis• Identify issues before they happen – Including: HVAC system, raised floor pressures ,airflow distribution, raised floor pressures, recirculation problems, cabinet airflow and server/switch inlet temperature• Remediate Hot Spots – Does IT equipment need to be moved or can thermal management solutions remediate?• Optimum IT Equipment Layout – Identify optimum growth areas• Spare Cooling Capacity – Is more cooling capacity required or can units be switched off or turned down?• What-If Analysis – Evaluate alternative solutions well ahead of implementation• Energy Savings – Fan energy : 20% decrease in fan speed can be a 50% decrease in fan energy. – Raising supply temperature can save 3 to 6% for every 1°C
  • 34. 42 • Visit us on the web: – – a smarter, unified foundationIf you have any additional questions or comments, please contact: Nick Taylor Follow us on Twitter at PanduitAdvisory
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