Case  study:  Energy  efficiency  improvements  in  a  legacy  data  centre  Robert  Tozer  Director  –  Opera>onal  Intelligence    

•  First  improve  air  management  –  Air  supply  temperature  to  servers  

•  Lower  temperature  •  Reduce  range  (also  control  CRAH  on  supply  air  temperature)  

•  Then  save  energy:  –  Increase  temperature  set  points  (chilled  water,  air):    

•  Refrigera>on  energy  (and  free  cooling)  

–  Reduce  air  flow  (to  what  is  required)    •  Fan  energy  (cube  law,  VFDs)  

Objec>ves  

Air  management:  improvements  •  Reduce  Bypass  flow  

–  Close  cable  penetra>ons  

–  Locate  air  grilles  in  front  of  IT  equipment  

•  Reduce  Recircula>on  flow  

–  Use  blanking  plates,  improve  rack  layout  

•  Reduce  Nega>ve  Pressure  flow  (<  air  velocity)  

•  Supply  air  control  (not  return  air  control)  

•  Physical  Containment  (cold  aisle,  hot  aisle  or  rack)  

Background  

0.3  1.0   0.4   =   $1.7m  

ANNUAL  SAVINGS  per  year  (1  site)  

Cooled  by  53  CRAH  units  

3,500m2  data    hall  area  

Current  IT  load  

1,800  kW  

Tier  3+  

2N  Built  in  2007  in  London  

Incremental  changes  in  a  

LIVE  ENVIRONMENT  

Energy  op>misa>on  programme  1.  Energy  assessment  and  data  hall  air  temperature  survey  2.  Outdoor  fresh  air  AHU  dew  point  control    3.  Air  management  improvements    4.  Reduce  fan  speeds  and  control  on  supply  air  5.  Increase  in  data  hall  air  set  points    6.  Increase  chilled  water  set  points  7.  Free  cooling  feasibility  study    8.  Installa>on  of  free  cooling  modifica>on  

PUE  reduc>on   1.49  

2.3  

$3m  

$4.7m  Annual  energy  

saving  

0   1  

1  

Flow  Performance  1-­‐BP  

Thermal  Perform

ance  

1-­‐R  

Af=0.25

Af=

4

BP  =  80%  R  =  20%    Af  =  4    Server  intake:  15  and  27°C  (upper  limit  ASHRAE  recommended  range)    Air  management  a  priority  

Energy  assessment/air  temperature  survey  

50%  IT  Load  

Data  cen

tre  load  re

la>ve  to  IT  

0   25%   75%   100%  

100%  

75%  

50%  

25%  

0  

125%  

150%  

175%  

200%  

 IT  PU

E  =  8  

C  

Original  

Ini>al  Load  

Improved  

Scalability  

Air  management  improvements  

15

Step 2: Air Performance � Measurement and Solution Air was recirculating around the end of the cold aisle and straight back into ����������� �������� �� ����������into the top of the racks. The installation of temp doors resulted in a reduction of approx. 5°C, increasing height of aisle by about 4°C, net result being an increase in the cooling effectiveness of the aisle � Temp solution mocked up to prove concept with a permamanant end of aisle solution then deployed. Recirculation coming over the top of the racks was combated by installation of flame retardant curtains to increase the height of cold aisle. Effective blanking within the racks also demonstrated significant improvements Total costs of deployment recovered in less than a year.

15

Step 2: Air Performance � Measurement and Solution Air was recirculating around the end of the cold aisle and straight back into ����������� �������� �� ����������into the top of the racks. The installation of temp doors resulted in a reduction of approx. 5°C, increasing height of aisle by about 4°C, net result being an increase in the cooling effectiveness of the aisle � Temp solution mocked up to prove concept with a permamanant end of aisle solution then deployed. Recirculation coming over the top of the racks was combated by installation of flame retardant curtains to increase the height of cold aisle. Effective blanking within the racks also demonstrated significant improvements Total costs of deployment recovered in less than a year.

Blanking  plates   Sealing  floor  gaps   Revised  floor  grille  loca>ons  

Proof  of  concept:  Hot  and  cold  air  

stream  segrega>on  

5C  reduc>on  4C  reduc>on  

1  year  payback:  deployed  throughout  data  hall  

CRAH  fan  speeds  and  control  

100%  

60%  

Original  fan  speed  

Op>mised  fan  speed  

Work  in  Progress:  40%  with  Dynamic  Control  

Fan  speed,  flow  rate  and  power  

20 Fan applicat ion guide

the impact that they have on the power requirement of thesystem overall.

In essence, if the load/speed of a fan never alters and isperfectly matched to its required output once installed,then the addition of a control can only reduce the systemefficiency. H owever, these conditions are rarely, if ever,encountered.

T he methods of duty control commonly employed areconsidered in the following sections.

5.2.1 Alteration of the fan rotational speed

See F igure 5.1. For a fan installed in a typical buildingventilation system, the power absorbed is approximatelyproportional to the cube of fan speed. Note that other(typically process) load types may have different charac-teristics.

In practice, the varying efficiency of motor and drivesystems with speed may modify th is ‘perfect’ controlcharacteristic.

Although larger fans may be driven by a wide variety ofprime movers, the majority of fans are driven by electricmotors.

In outputs above 200 W, these are typically AC inductionmotors where the rotational speed is dependant on supplyfrequency and internal construction and having efficien-cies that vary from 60 to 90%+ , over the range to 75 kW.In smaller sizes, where AC motor efficiency may be as lowas 20%, recent developments in DC motor technology haveseen these used with the benefits of lower losses and morestable speed controllability.

Where infrequent duty changes are needed, the use of beltdriven fans, with high efficiency drive systems is oftenused for decreasing fan speed and operating at speedsother than those provide by standard motors (note thatany increase in speed generally requires reference to thefan manufacturer).

Belt/pulley changing requires a degree of skill, and someconsiderable downtime, these factors being the principaldisadvantages together with the power loss inherent in thedrive.

More frequent speed changes with fixed ratios (usually of1:2 or 1:1.5) may be achieved at relatively low cost withmulti-speed AC motors and basic electrical switchgearunder automatic (e.g. time based) or manual control.

For smaller induction motors (up to around 2.2 kWoutput) the possibility exists for variable speed operationusing a fixed frequency, variable voltage speed controller,of either a transformer or solid state (triac) based type.The latter tend to be smaller and lower cost but may causemotor noise due to their non-sinusoidal output waveform.

A degree of two-speed operation can be achieved in thisoutput range by using a star/delta wiring changeover,which produces an effective voltage control.

The reason for the stated limitation in motor output is thetemperature increase in the motor due both to increasedlosses and the reduced ability to reject heat as speeddecreases.

The motor and/or control may fail if they are not correctlymatched. Typically a peak in motor current occurs ataround 65% of maximum speed and must be allowed for.Specifiers are strongly advised to seek the approval of thefan manufacturer for any speed control device used, and toensure that all products comply with the latest legislativerequirements.

Undoubtedly, one of the most significant technologicaladvances in the past 30 years has been the availability ofcost effective variable frequency speed control drives(often known as ‘inverters’), in output ratings from 150 Wto several thousand kilowatts.

By varying the effective supply frequency to the motor,speed reductions down to 20% may be achieved withoutsignificant de-rating. T his technique is applicable to awidely available range of suitable motors.

T hese products have made practical a wide range ofsophisticated control possibilities and the ability tointerface easily with building management systems.

The power conversion efficiency of such drives is typicallyabove 96%, although the imperfect output waveform mayreduce peak motor efficiency by 1 or 2 %. Motor efficiencymay itself reduce significantly at speeds below 75%.

There are many manufacturers of these devices, offeringmany advanced features. A limitation on their use hasbeen the lack of experience of H VAC installers with thetechnology, particularly with regard to electromagneticemissions and immunity.Figure 5.1 Flow control by speed regulation

1

2

3

75% full speed

Design operatingpoint

Fan outputcharacterist ics

Fan powercharacterist icat full speed

50% full speed

Full speed

75% full speed

50% full speed

Volume flowrate, qv

Fan

stat

ic pr

essu

re, p

sFa

n sh

aft p

ower

, Pr

Pr1

ps2

ps1

ps3

qv3 qv2 qv1

Pr2

Pr3

Fan  Applica*on  Guide    CIBSE  TM42:  2006  

0.3  

1.0  

0.4  

$million  savings/yr  

COP  chilled  water  +  chiller  delta  T  

 

15-­‐17/24°C    

6/12°C    

22°C    Supply  Air  

24°C    Return  Air  

Chilled

 water  

tempe

rature  se

t  po

ints  

Cooling  un

it  set  

points   FR

OM  

FROM  

TO  

TO  

Set  points  

Opera>ng  envelope  for  humidity  control  widened  in  line  with  ASHRAE  recommenda>ons  

Ven>la>on  &  addi>onal  chw  temp  

Small  number  of  hours  above  15°C  dew  point  

0.3  

1.0  

0.4  

$million  savings/yr  

ven>la>on  extract  fan  Ven>la>on  flow  rates  

50%  RH  5.5°C    

dew  point  

Psychrometric  chart  

!

Key  decisions  •  Choice  of  free  cooling  system  

– Choice  of  an  evapora>ve  system  – No.  of  heat  transfer  processes  

•  Area  of  heat  exchangers    – CAPEX  – OPEX   Q  =  A  .  U.  LMTD  

Q        =  cooling  (kW)  A        =  area  (m2)  U                    =  heat  transfer  coefficient  (kW  /  K  m2)  LMTD    =  log  mean  temperature  difference  (K)    Given  fixed  Q  and  U  then  LMTD  α  1/A  

T  

Air  Data  Hall  23°C    

12°C      

6°C  

Chilled  water  

Total  Appr  27  K    

BP  

31°C    T  

27°C  

Total  Appr  12K      

BP  

22°C    R  

23°C  

R  

-­‐4°C    

Free  cooling  Outside  air  

2°C    

23°C    

21°C  

31°C  

22°C  

18°C  

15°C  

11°C  

Heat  exchange  area  Before  

Heat  exchange  area  Arer  

Free  cooling  feasibility  study  

Chillers   CRAH  units  

Buffer  tanks  

Primary  circuit   Secondary  circuit  

Dry  coolers  /  Cooling  towers  

Dry  coolers  

Capacity  

Approach  temperature  

CRAH  cooling  coils  

Free  cooling  feasibility  study  –  best  op>on  

!

Predic>on:  

Free  cooling  feasibility  study  

Installa>on  of  free  cooling    with  dry  coolers  

0.3  

1.0  

0.4  

$million  savings/yr  

Year  1  

Fiscally  posi>ve  

3  years  

ROI  less  than  

0   1  

1  

Flow  Performance  1-­‐BP  

Thermal  Perform

ance  

1-­‐R  

Af=0.25

Af=

4

ORIGINAL:  BP  =  80%  R  =  20%    Af  =  4    

 IMPROVED:  BP  =  42%    R  =  9%    Af  =  1.57  

Air  performance  arer  improvements  

7

PUE Benchmarking: Continued Year-On-Year Improvement

3.38

1.98

1.71 1.68 1.69 1.61

1.48

1.300

1.800

2.300

2.800

3.300

CDC Q1 YonY Performance 2.87

1.96

1.74 1.70 1.70 1.66

1.53

1.300

1.500

1.700

1.900

2.100

2.300

2.500

2.700

2.900

CDC Q2 YonY Performance

2.58

2.06

1.72 1.78

1.68 1.74

1.54

1.300

1.500

1.700

1.900

2.100

2.300

2.500

2.700

CDC Q3 YonY Performance

2.36

1.84

1.67 1.63 1.62

1.65

1.47

1.300

1.500

1.700

1.900

2.100

2.300

2.500

CDC Q4 YonY Performance

A) ������������������������� ���� ����������� ������������ B) Reduction in PUE directly attributed to energy efficiency initiative

A B

0.3  1.0   0.4   =   $1.7m  

ANNUAL  SAVINGS  per  year  

1.41  Instantaneous  PUE  1.49  Es>mated  annual  PUE  

35%  Overall  reduc>on  

Conclusions  

Dec  1st  @  11:00  2050KW  of  Heat  RejecLon  for  10KW  electrical  energy.  COP  of  205  @  7.6  degC  ambient  vs  ~COP  3  from  Chillers  

Annual    PUE  Trend  YTD                                                                                                                                                                                                                                                            Note  :  DAC  Turned  on  in  Dec  13  

DAC  ON  

Conclusions  

Conclusions  

16

Step 3,4,5 : Changing Set Points, Reducing Fan & Pump Speeds PUE � Improvement of 34% IT Load (69%) � No Change for evaluation UPS Transformation Losses (7.5%) � We have rotary machines that are operating at 90% efficiency so

a fixed loss at present, albeit we matched capacity to load where possible

Lighting and ancillary loads (10%) � Reducing Lighting footprint and run hours, re-educating users, ��������������������� ���

Secondary Pumps (1%) � To re-balance CHW flow rate to cooling load, saves pumping ���

Data Hall Air Movement (7%) � Achieve better control of air distribution, re-balance air flow rate to ����������������������� ��������������� ���

� Change CRAC control Strategy to supply air, decrease fan speed (cube law benefits)

Chiller and Primary Pumps (7.5%) � Raise temperature of CHW to improve COP of the chillers. Re-

balance CHW flow rate to match secondary load, saves pumping ���

� Adjust humidity control window, reduce humidifier hrs � Install Free Cooling benefit from much higher COP � Ability to turn off primary pumps when in 100% free cooling mode

Initiative to date : PUE ~1.49

Pre Initiative : PUE ~2.29

Indicative Graph showing Impact to PUE of Raising Chilled Water Temperatures

UPS  Op>

misa

>on  

Con>

nued

 increase  

Data  hall  supply  temperature  

26C  

Chilled  water  temperature  

21/28C  

Free  cooling    hours  

2-­‐3%  

Further  savings  

Our  workshops  are  accredited  by  CIBSE    

RobertTozer@dc-­‐oi.com  www.dc-­‐oi.com  

www.linkedin.com/company/opera>onal-­‐intelligence-­‐ltd  @OI_RobertTozer  

Ques>ons?