Lowering operating costs through cooling system design

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Learn more about achieving maximum energy efficiency through cooling system design. This presentation was given during the Spring 2012 Data Center World Conference in Las Vegas, NV. Learn more by visiting www.datacenterworld.com.

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Lowering operating costs through cooling system design

  1. 1. Interested in data center power and cooling? Learn about data center efficiency/power & cooling sessions offered at the upcoming Fall 2012 Data Center World Conference at: www.datacenterworld.com.This presentation was given during the Spring, 2012 Data Center World Conference and Expo.Contents contained are owned by AFCOM and Data Center World and can only be reused with theexpress permission of ACOM. Questions or for permission contact: jater@afcom.com.
  2. 2. Lowering Operating Costs Through Cooling System Design Paul Bemis President Applied Math Modeling Inc 2
  3. 3. Data Center PUE (Power Utilization Effectiveness) Total Facility Energy PUE = IT Energy How effectively is my facility delivering cooling to my IT equipment?Total Facility IT Equipment • Servers Power • Storage • Telco • etc 3
  4. 4. PUE and DCiE Power Utilization Effectiveness (PUE) PUE = Total Facility Energy / Total IT EnergyData Center Infrastructure Efficiency (DCiE) DCIE = (Total IT Energy/ Total Facility Energy) x100% 4
  5. 5. Some Facts About PUE• Dominant Parameters are IT and Cooling Energy. – CRAC/Chiller make up 75% of total “non-IT” load • UPS, PDU, Switchgear are all 2nd order effects 5 Source: Uptime Institute
  6. 6. Data Center PUE (Power Utilization Effectiveness) Cooling Energy + IT Energy PUE = IT Energy How effectively is my facility delivering cooling to my IT equipment?• Focusing on Cooling Efficiency provides largest payback• Understanding how cooling systems operate is key 6
  7. 7. Cooling System Energy Efficiency• Cooling Units (heat pumps) – Use mechanical shaft power provided by an electric motor to perform the work necessary to move heat from one location (inside) to another (outside). – The Coefficient of Performance (COP) of a heat pump is the ratio of the heat pumped (moved) to the supplied work. – The COP for Data Center Cooling ranges from 2-5* Thermal Load In Room COP = ∆Q ∆W Energy Required to Drive Heat Pump * Patnaik, Marwah, Sharma, Ramakrishnan Department of Computer Science, Virginia Tech, “Sustainable Operation and Management of Data Center Chillers” 7
  8. 8. Data Center PUE (Power Utilization Effectiveness) IT Energy/COP + IT Energy PUE = IT Energy 1 => PUE = Good Approximation COP + 1• The COP of the data center cooling system is the dominant parameter in the PUE calculation.• The COP can be easily measured in existing data centers. – Ratio of total IT load/ ATS switch load 8
  9. 9. How does COP relate to “Set Points”?• Increasing Cold Air Supply increases COP at a rate of 3.5% for every 1.8F From ASHRAE 90.1-204, Table 6.8.1 I 9
  10. 10. Schematic and T-s Diagram for IdealVapor-Compression Refrigeration Cycle Reducing compressor “Lift” will reducing energy consumption.. 10
  11. 11. Techniques for Improving the Efficiency of Data Center Cooling Systems• Maximize the temperature difference across all heat exchangers – Increase hot air return temperature in data center• Increase the cold air supply temperatures as high as possible, while maintaining ASHRAE inlet temperature guidelines 11
  12. 12. Maximizing Heat transfer in the Data Center• Each CRAC/CRAH utilizes a fan/coil system for transferring heat from the data center.• The governing equation for heat transfer is: Q = mcP (TR − TS )  Heat Mass Flowrate Specific Heat of air• It is important to maximize the temperature difference across the coil.• It is also important to balance the mass flow rates between the IT load and the CRAC/CRAH units 12
  13. 13. Steps to optimize cooling efficiency (and reduce operating costs)• Determine the total amount of airflow required to satisfy IT thermal load. – Use 156 CFM/KW as a ‘rule of thumb’• Strive to reduce the supply airflow to match only what is needed by the servers – Maximizes return air temperatures and saves operation costs on fan energy.• Begin to increase air supply temperature until worst case rack/server reaches 80.6F – Use containment to unify rack inlet temperatures 13
  14. 14. Rack Flow Rate Return Temperature Index (RTI)™ = x 100 Air Handler Flow Rate or Air Handler Delta T Return Temperature Index (RTI)™ = x 100 Rack Delta TRTI is a measure of net by-pass air ornet recirculation air in the data center Return Temperature Index (RTI) is a Trademark of ANCIS Incorporated (www.ancis.us). All rights reserved. Used under authorization 14
  15. 15. Total Over-Temp Rack Cooling Index (RCIHI) =1 - ® x 100 Max Allowable Over-Temp Total Under-Temp Rack Cooling Index (RCILO) = - 1 ® x 100 Max Allowable Under-Temp ASHRAE Recommended AllowableSpecifications: 64.4 – 80.6 F 59 – 89.6 F RCI is a measure of compliance with the ASHRAE thermal guideline Rack Cooling Index (RCI) is a Registered Trademark of ANCIS Incorporated (www.ancis.us). All rights reserved. Used under authorization 15
  16. 16. Example Data Center• Data Center is a raised floor design of 1600 sq ft, 145 kW of IT load, and natural convection return.• DX based perimeter downflow cooling capacity is 325kW, 255kw nominal (N+1). – Ratio of 1.76x required cooling capacity – Controlled individually, and are constant volume devices• Interested in reconfiguring data center to improve efficiency – Lower operational costs – Increase “headroom” for future IT load• Would like to predict the ROI of proposed changes: – Cold/hot aisle containment – VFD’s to improve the balance of supply/return airflow. 16
  17. 17. Analysis Outline• Perform baseline analysis on existing equipment – Currently uses 4 Lieberts (2-DH412W, 2-DH315W) • Validate CFD Model • Perform baseline energy calculations• Study alternatives for optimizing RTI – Investigate shutting down CRAC units or implementing VFD’s – Investigate the need to add containment curtains• Begin to increase cold air supply temperature – Watch racks inlets until worst case temperature reaches 80F 17
  18. 18. Baseline Model Using Factory Specs 18
  19. 19. Model Validation Factory Specifications Supply Temp Return TempCrac Number Flowrate (CFM) Measured Predicted Measured Predicted 1 12,000 61.2 61 72 69 2 12,000 60.1 60 73 66 3 15,200 56.5 57 74 69 4 15,200 65 65 74 73 54,400 60.7 60.75 73.25 69.25 Q = mcP (TR − TS )  Base Case Specifications Supply Temp Return TempCrac Number Flowrate (CFM Measured Predicted Measured Predicted 1 10,000 61.2 61 72 74 2 9,000 60.1 60 73 68 3 10,000 56.5 57 74 71 4 10,500 65 65 74 76 39,500 60.7 60.75 73.25 72.25 19
  20. 20. Base Case Colo FacilitySpecificationsRoom di mens i ons 28 X 58.5 X 10 feetRoom fl oor a rea 1625.5 s q. ft.Suppl y plenum hei ght 1.5 feetNumber of downfl ow CRAC units 4Number of rack rows 20Tota l number of racks 59Number of ti le rows 10 Energy Savings OpportunityTota l number of til es 59Airflow AssessmentSuppl y a ir fl ow rate from downfl ow CRACs 39500 CFMDemand a ir fl ow rate from ra cks 22559 CFMTota l demand ai r fl ow ra te 22559 CFMSuppl y a ir fl ow ratio(%) 175% (75% exces s of the demand ai r flow ra te.)Es ti ma ted average fl ow rate through perforated ti les 669 CFMEs ti ma ted average pres s ure drop acros s the ti l es 0.281 l bf/ft2Thermal AssessmentEs ti ma ted heat dens i ty 89.02 W/s q.ft. of room a reaEs ti ma ted downflow CRAC cool i ng capa ci ty 254.94 kWEs ti ma ted s uppl y a ir tota l cool i ng capa ci ty 254.94 kWEs ti ma ted tota l rack heat l oa d 144.7 kWTota l IT cool ing l oa d 144.7 kWCool ing ca pa ci ty to heatLoad rati o(%) 176% (76% exces s than cooli ng demand)Es ti ma ted tempera ture ri s e of s upply ai r 11.35 FEs ti ma ted average tempera ture of hot a ir 71.35 F(for 60 F s upply a ir tempera ture) 20
  21. 21. 144 KW Base Case Selected Results Base Case 144 KW DX IT Heat Load 144.7 kW 5% IT Infrastructure 7 kW Total IT Heat Load 152 kW Total Cooling Power 143 kW Total Supply Air Flow 39,500 CFM Total Demand Air Flow 22,559 CFM Fan Power 67 kW Average Supply Temp (F) 60.75 F COP 1.53 RTI 57% Nearly 2x the amount of airflow required RCI hi 100% No racks out of ASHRAE High Temp guidelines RCI lo 44% More than half out of ASHRAE Low Temp guidelines Total Facility Power 362 kW PUE 2.38 Baseline PUE estimateAssumed Cost of Electricity 0.08 $/kW-Hr Annual Cost 253,751 $ Costing as much to cool servers as to power them… 21
  22. 22. ASHRAE Conformance Plot 22
  23. 23. Motives for Change• RTI of existing data center is 57%, indicating nearly 100% bypass airflow.• Current DX units do not support VFD, so reducing supply airflow is limited to shutting off CRACs – Would require backflow prevention and ICON control• Moving to new DX CRAC’s will provide the following benefits: – Allows VFD’s plug fans so demand/supply airflow match (RTI = 100%) – Provides increased upside cooling capacity – Increases COP by a factor to at least 3 • Which significantly reduces the energy consumption of cooling system. Modeling can be used to accurately predict results prior to implementation… 23
  24. 24. Step 1: 144KW Contained Case Results Fans @ 80% 24
  25. 25. Step 1: 144KW Contained Case Results Fans @ 80% 25
  26. 26. Step 1: 144KW Contained Case ASHRAE Conformance 26
  27. 27. Step 1: New DX Units Fans @80% and Contain Cold Aisle Base Case Contained Case 144 KW DX 144 KW DX IT Heat Load 144.7 144.7 kW 5% IT Infrastructure 7 7 kW Total IT Heat Load 152 152 kW Total Cooling Power 143 64 kW Total Supply Air Flow 39,500 32,000 CFM Lowered by 20% Total Demand Air Flow 22,559 22,559 CFM Fan Power 67 40 kW Lowered by 40% Average Supply Temp (F) 60.75 60.75 F COP 1.53 3.00 Improved by factor of 2x RTI 57% 70% Improved by 23% RCI hi 100% 100% No racks exceed high temps RCI lo 44% 34% RCI dropped, racks too cold Total Facility Power 362 255 kW PUE 2.38 1.68 PUE headed in right directionAssumed Cost of Electricity 0.08 0.08 $/kW-Hr Annual Cost 253,751 179,027 $ Projected Savings 74,724 $ % Savings per Year 29% Can we drive up Air Supply Temp? 27
  28. 28. 144KW Contained Case Results Fans @ 80% Ts=70F 28
  29. 29. Step 2: Lower Fans 20%, Contain Cold Aisle, and Increase Supply Temp to 70F Base Case Contained Case Contained Case 144 KW DX 144 KW DX 144KW 70F IT Heat Load 144.7 144.7 144.7 kW 5% IT Infrastructure 7 7 7.2 kW Total IT Heat Load 152 152 151.9 kW Total Cooling Power 143 64 54 kW Total Supply Air Flow 39,500 32,000 32,000 CFM Total Demand Air Flow 22,559 22,559 22,559 CFM Fan Power 67 40 40 kW Average Supply Temp (F) 60.75 60.75 70.00 F COP 1.53 3.00 3.54 RTI 57% 70% 70% RCI hi 100% 100% 100% No racks exceed high temps RCI lo 44% 34% 100% No racks exceed low temp Total Facility Power 362 255 246 kW PUE 2.38 1.68 1.62 PUE continues to improve Assumed Cost of Electricity 0.08 0.08 0.08 $/kW-Hr Annual Cost 253,751 179,027 172,204 $ Projected Savings 74,724 81,547 $ % Savings per Year 29% 32% Can we improve RTI a little more?? 29
  30. 30. Step 3: Lower Fans 37%, Contain Cold Aisle, Supply Temp 70F 30
  31. 31. Step 3: Lower Fans 37%, Contain Cold Aisle, and Increase Supply Temp to 70F Contained Case Base Case Contained Case Contained Case 144KW 70F Lower 144 KW DX 144 KW DX 144KW 70F Fans 37% IT Heat Load 144.7 144.7 144.7 144.7 kW 5% IT Infrastructure 7 7 7.2 7.2 kW Total IT Heat Load 152 152 151.9 151.9 kW Total Cooling Power 143 64 54 49 kW Total Supply Air Flow 39,500 32,000 32,000 25,000 CFM Total Demand Air Flow 22,559 22,559 22,559 22,559 CFM Fan Power 67 40 40 21 kW Average Supply Temp (F) 60.75 60.75 70.00 70.00 F COP 1.53 3.00 3.54 3.54 RTI 57% 70% 70% 90% RTI has improved 20% RCI hi 100% 100% 100% 97% Some racks exceed high temps RCI lo 44% 34% 100% 100% No racks exceed low temp Total Facility Power 362 255 246 222 kW PUE 2.38 1.68 1.62 1.46 PUE continues to improveAssumed Cost of Electricity 0.08 0.08 0.08 0.08 $/kW-Hr Annual Cost 253,751 179,027 172,204 155,788 $ Projected Savings 74,724 81,547 97,963 $ % Savings per Year 29% 32% 39% Lowers overall operating costs by 39% 31
  32. 32. Step 3: Lower Fans 37%, Contain Cold Aisle, Supply Temp 70F 32
  33. 33. Analysis Summary• The combination of VFD’s and Cold Aisle Containment yield the following benefits – Deploying newer technology DX units and lowering fans speeds improves RTI, RCI, PUE, and reduces energy costs considerably. – Installing cold (or hot) aisle containment improves air management and allows cold air supply temperature to be increased, which improves cooling efficiency• Doing both these things reduces overall energy consumption by an estimated 39%, saving ~$100k per year in operational costs.• Estimated cost to implement these changes is $300k, providing a ROI of 3 years (excluding energy rebate credits) 33
  34. 34. For more information• Questions Regarding This Presentation and/or Modeling Methods – Paul Bemis – Paul.Bemis@CoolSimSoftware.com• For Information, please contact: – Applied Math Modeling Inc, – Jennifer Beliveau – Jennifer.Beliveau@CoolSimSoftware.com 34
  35. 35. Interested in data center power and cooling? Learn about the data center efficiency/power & cooling sessions offered at the upcoming Fall 2012 Data Center World Conference at: www.datacenterworld.com.This presentation was given during the Spring, 2012 Data Center World Conference and Expo.Contents contained are owned by AFCOM and Data Center World and can only be reused with theexpress permission of ACOM. Questions or for permission contact: jater@afcom.com.

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