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STULZ THE NATURAL CHOICE
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Best Practice - Data Centre Cooling 1
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Best Practice - Data Centre Cooling 2
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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Best Practice - Data Centre Cooling 3
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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Best Practice - Data Centre Cooling 7
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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7. Airflow philosophies
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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7. Airflow philosophies
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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7. Airflow philosophies
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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7. Airflow philosophies
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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7. Airflow philosophies
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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7. Airflow philosophies
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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7. Airflow philosophies
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%
40%
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70%
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90%
100%
Airf low Absorbed Power
0%
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20%
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Airf low Absorbed Power
1/2
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)
3x 146,8 kW = 440,4 kW net sensible
Airflow: 4x 29.000 m/h
Fan power = 4x 5,3 kW = 21,2 kW
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
11. Standby Unit Operation
Therefore, by running the stand-by CRACunit at reduced air volume the overall
fan power is greatly reduced.
Example:
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4x 110,3 kW = 441,2 kW net sensible
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:
Airflow: 4x 27.800 m/h
Fan power = 4x 4,7 kW = 18,8 kW
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
11. Standby Unit Operation
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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.