stulz data c climatiseur entre cooling

8/10/2019 stulz data c climatiseur entre cooling

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STULZ THE NATURAL CHOICE

01/2010

Best Practice - Data Centre Cooling 1


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1. INTRODUCTION

2. AIR FLOW LEAKAGE3. PERFORATED TILES: NUMBER AND OPENING FACTOR

4. PERFORATED TILES: WITH ADJUSTABLE DAMPER

5. PERFORATED TILES: PLACEMENT

6. CLOSE UNUSED UNITS IN THE RACKS WITH BLANKING PANELS TO

AVOID AIRFLOW SHORT CIRCUIT INSIDE THE RACK

7. AIRFLOW PHILOSOPHIES

8. RAISED FLOOR HEIGHT

9. RETURN AIR CONDITIONS

10. CHILLED WATER SYSTEM WATER CONDITIONS

11. STANDBY UNIT OPERATION

12. USE CRAC UNITS WITH STATE-OF-THE-ART COMPRESSOR AND FAN

TECHNOLOGY


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1. Introduction

This presentation summarises todays Best Practise for data-centre cooling

systems.

It will give you a rough overview about all concerned parts of the data-centre.

This lis t is not exhaustive, but it will impart the most important matters how to

design, build and run an as energy efficient as poss ible data-centre.


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2. Airflow Leakage

Airf low leakages (short air circuit) leads to dramatic inefficienciesdue to air ci rculation back to the CRAC unit w ithout taking heat from

the computer equipment.

Close all unwanted openings in the raised floor

Close all unwanted openings below the racks

Close all cable cut outs use cable sealings

Al l gaps (near walls and CRAC units) have to be sealed


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2. Airflow Leakage

The target is to create an overpressure under the raised floor torealize an even air supply to all areas of the data-centre.

This overpressure can only be achieved w ith an as low as possible

amount of unwanted airflow leakage.

A maximum loss of 2 6% of the total

airflow of the data-centre is acceptable.


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3. Perforated Tiles: Number and Opening Factor

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Tile number

Example (Data-centre):

Design airflow: 50.000 m/h, ESP 20Pa

Chosen ti le: airf low : 500m/h, 20Pa 100 tiles are required

Actual aif low : 30.000 m/h,

Tile number to be reduced to 60

Only a raised floor with sufficient

height and perforated tiles

with limited openings allow an

even air distribution !!!

The number of perforated tiles must be in line with:

A) the designb) the actual / real airflow


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4. Perforated Tiles: With Adjustable Damper

Perforated ti les with integral adjustable

dampers can be used to avoid having to

replace perforated tiles with sol id tiles.

In this case the number of perforatedtiles can remain unchanged but all ti les

need to be adjusted according to the

actual requirements in the room.

It is also possib le to work with different adjustments to vary the amount of

air in different areas of the data-centre.

In any case the static pressure under the raised floor has to be kept at the

design level.



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5. Perforated Tiles: Placement

Perforated tiles should only be

placed at posi tions, where cold

air is really required to cool

equipment.

Do not place perforated tiles directly near the CRAC unit; a distance of minimum

2m has to be kept. Perforated tiles near CRAC units can induce warm room air into

the raised floor (negative airf low).



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6. Close Unused Units in the Racks with Blanking Panels

Recirculation of cooling air

inside the rack leads to

overheating of servers.

Blanking panels installed

in unused areas or slots of

a rack eliminate a possib le

internal recirculation of the

hot air.



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7. Airflow philosophies

A) The old/traditional way:

Uncontrolled placement ofperforated supply air tiles

anywhere in the room

Cold air is supplied in anuncontrolled way to the low

density equipment

Uncontrolled recirculation Supply and return air mixing

takes place

NOT RECOMMMENDEDANYMORE Very inefficient



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B) Hot Aisle, Cold Aisle Concept:

Hot/Cold AisleConcept

Cold supply air distribution only in the cold aisles Warm return air only in the hot aisles Open tiles only in the cold aisle Risk of mixing cold and hot air is high This risk can be reduced by using suspended

ceilings



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C) Hot Aisle Containment:

Hot Aisle

Containment

Hot Aisle between the racks will be covered on the top and the end ofrack rows Cold supply will be delivered into the room Open tiles only in the room Full separation between supply and return air The room itself will be at low temperature level



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D) Cold Aisle Containment:

Cold Aisle

Containment

Cold supply air distribution only in the cold aisles

The cold aisle is separated from the hot aisle Warm return air only in the hot aisles Open tiles only in the cold aisle No risk of mixing cold and hot air The room itself will be at high temperatures



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Debate: Hot aisle or cold aisle containment ???

Keeps the hot air in a confined area.

The room outside is cold.

Servers are stable and can be operated

for an extended period in case of loss

of airflow.

Hot Spots in the cold aisle disappear.

Overall stabil ity can be increased.

Disadavantage:

CRACs have to be calculated carefully

to deal with the high return air

temperatures.

Keeps the cold air in a confined area, no need

to cool the entire space.

Floor space around the cold aisle is warm.

Disadvantages:

Air balancing can be di ffi cult if CRACs are

sequencing and the raised floor pressure ischanging.

In case of power outage the cold ais le is

exposed to high threat due to loss of airflow .

Control of supply air temperature with DX-units

only possible to a certain extend.



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E) Room Supply, Direct Rack-Out Return Concept:

Room supply,

Ducted return air

Cold supply air enters the rack through the room Open tiles only in the cold aisle Warm return air leaves the rack through a duct and suspended ceiling Full seperation of hot and cold air The room itself will be at low temperature level


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F) Close Coupling of CRAC units and Racks on Supply and Return Side:

Ducted Supply and

Return Air Concept

Cold supply air into ducts fitted to the supply air side of the racks Warm return air through ducts fitted to the exhaust side of the racks Open tiles only in the area of supply air ducts No risk of mixing cold and hot air


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Summary:

Target of all these various possibilities is the complete separation of warmreturn air and cold supply air

This separation leads to an increased temperature difference betweenreturn and supply air temperature of the CRAC unit

A high temperature difference increases the efficiency of the CRAC unitand therefore the efficiency of the data-centre in general

What kind of separation can be used in a data-centre is depending on thesituation and used equipment

The highest level of efficiency is reached if each m of circulating air takesthe design amount of heat from the IT-euipment


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8. Raised floor height

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Tile number

Rule of thumb:

The higher, the better !

The raised floor height has got a

major influence on the efficiency

of the whole data-centre !

The required free height is

depending on room size, heatdensity and number and position

of instaled CRAC units.

A certain obstacle free area is

required for a proper supply of

cold air to any area of the room !


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The leading and most important temperatureis the air entering the IT equipment (server).

According to the new ASHRAE environmental

envelope supply air temperatures up to 27C

are possible. That would lead to return air

temperatures of approx. 37C.

Please note: A low return air set-point does not

cure problems with heat load. It is the other

way around: The lower the return air set-point

the lower the usable cooling capacity of the

unit. Furthermore the operating costs are

increasing.

High return air temperatures and lower return

air humidity do not change the content of

water in the room. The risk of ESD is as low.

8K

35C

27C

9. Return Air Condit ions


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Advantages of high return air temperatures:

(1) CW-units: High return air temperatures are leading towards higher

water temperatures (with same sensible cooling capacity). The

starting temperature of the free-cooling is much higher.

(2) CW-units: To get the same cooling capacity with high return airtemperatures and high water temperatures the airflow of the unit can

be reduced. Lower airflow leads to lower fan power consumption and

a lower noise level.

(3) DX-units: Higher return air temperatures are leading towards higher

evaporating pressure. With constant condensing pressure the delta

between evaporating and condensation pressure is reduced. The

compressor power consumption is decreasing. Furthermore the fan

speed also can be reduced.

But please be aware that too high evaporating pressure can damage

the compressor.

9. Return Air Condit ions


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10. Chilled Water System Water Conditions

Heat loads in data-centres are nearly allsensible cooling load with only a small latent

cooling load due to fresh air ventilation.

In accordance to the increased return air

temperatures the chil led water temperatures

can be increased as well.

Chiller efficiency will be increased due to increased evaporating temperature.

The higher the chil led water temperature the earlier the starting temperature

of the chiller free-cooling.

The balance between cool ing capacity of the CRAC unit and chiller efficiency

has to be evaluated.


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11. Standby Unit Operation

Fan laws dictate that air volume is directly proportional to fan speed and that fan

power is a cube of the fan speed.

0%

10%

20%30%

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100%

Airf low Absorbed Power

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Airf low Absorbed Power

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Airflow 1/8

Absorbed

Power


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4x ASD1900CW at 26C/40%

Water 10/15C

Standby

4x 114,6 kW = 458,6 kW net sensible

Airflow: 3x 39.000 m/h

Fan power = 3x 12,6 kW = 37,8 kW

Lpa,2m = 3x 71,6 dB(A) = 76,4 db(A)




Lpa,2m = 4x 62,7 dB(A) = 68,7 db(A)

=> Energy savings:

16,6 kW x 8760h x 0,13 = 18.904 /year @ 0,13 /kWh


Therefore, by running the stand-by CRACunit at reduced air volume the overall

fan power is greatly reduced.

Example:


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Reduction of fan power consumption

Reduction of noise level

Increase of net sensible cooling capacity And: even more energy can be saved if net sensible coolingcapacity is kept constant:

Advantages of Standby-Management:



Lpa,2m = 4x 61,5 dB(A) = 67,5 db(A)

=> Energy savings:

19,0 kW x 8760h x 0,13 = 21.637 /year @ 0,13 /kWh



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12. Use CRAC Units with state-of-the-art Technology

EC fan technology:

Advantages:1. Lower power consumption due to better overall degree of efficiency

2. No in-rush current, speed is ramped up, never draws more than full load amps

3. Low vibrat ion reduced sound level

4. Long maintanance free operation due to direct drive technology

5. Scalable air flow easy adaptation on requirements on site
http://../Pfleiderer/Lokale%20Einstellungen/Temporary%20Internet%20Files/OLK45/Copy%20of%20new09_2006_EC%20Fan%20Energy%20CCD2300CWE%20Final%20September05.xls


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B t P ti D t C t C li

Example:

Munich airport data centre, source:

600 m data centre, 75 server cabinets arranged in 3 rows

5 CRAC units (4+1), each 32 kW cooling capaci ty

Changes (Best practise only ):

installation of hot aisle/cold aisle containment

re-routing cables inside the racks

reconfiguring of floor tile layout, sealing of raised floor

installation of 1U blanking panels at the front of the racks installation of ventilated front doors

increasing of room temperature to 28C (supply air = 22C)

=> Due to these changes the power consumption of the CRAC units are reduced by 35%.

=> Cabinet temperatures are reduced by 4C extended lifetime of servers and more reliabil ity.

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stulz data c climatiseur entre cooling