Stulz datacentre cooling

STULZ – THE NATURAL CHOICE
01/2010
Best Practice - Data Centre Cooling 1

01/2010
1. INTRODUCTION
2. AIR FLOW LEAKAGE
3. 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

01/2010
1. Introduction
This presentation summarises today´s „Best Practise“ for data-centre cooling
systems.
It will give you a rough overview about all concerned parts of the data-centre.
This list is not exhaustive, but it will impart the most important matters how to
design, build and run an as energy efficient as possible data-centre.

01/2010
2. Airflow Leakage
Airflow leakages (short air circuit) leads to dramatic inefficiencies
due to air circulation back to the CRAC unit without 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
• All gaps (near walls and CRAC units) have to be sealed

01/2010
2. Airflow Leakage
The target is to create an overpressure under the raised floor to
realize an even air supply to all areas of the data-centre.
This overpressure can only be achieved with 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.

01/2010
3. Perforated Tiles: Number and Opening Factor
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Tile number
Example (Data-centre):
Design airflow: 50.000 m³/h, ESP 20Pa
Chosen tile: airflow: 500m³/h, 20Pa
⇒ 100 tiles are required
Actual aiflow: 30.000 m³/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 design
b) the actual / real airflow

01/2010
4. Perforated Tiles: With Adjustable Damper
Perforated tiles with integral adjustable
dampers can be used to avoid having to
replace perforated tiles with solid tiles.
In this case the number of perforated
tiles can remain unchanged but all tiles
need to be adjusted according to the
actual requirements in the room.
It is also possible 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.

01/2010
5. Perforated Tiles: Placement
Perforated tiles should only be
placed at positions, 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 airflow).

01/2010
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 possible
internal recirculation of the
hot air.

01/2010
7. Airflow philosophies
A) The „old/traditional“ way:
• Uncontrolled placement of
perforated supply air tiles
anywhere in the room
• Cold air is supplied in an
uncontrolled way to the low
density equipment
• Uncontrolled recirculation
• Supply and return air mixing
takes place
• NOT RECOMMMENDED
ANYMORE
• Very inefficient

01/2010
B) Hot Aisle, Cold Aisle Concept:
Hot/Cold Aisle
Concept
• 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

01/2010
C) Hot Aisle Containment:
Hot Aisle
Containment
• Hot Aisle between the racks will be covered on the top and the end of
rack 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

01/2010
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
• No risk of mixing cold and hot air
• The room itself will be at high temperatures

01/2010
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 stability can be increased.
Disadavantage:
CRAC´s 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 difficult if CRAC´s are
sequencing and the raised floor pressure is
changing.
In case of power outage the cold aisle is
exposed to high threat due to loss of airflow .
Control of supply air temperature with DX-units
only possible to a certain extend.

01/2010
E) Room Supply, Direct Rack-Out Return Concept:
Room supply,
Ducted return air
• Cold supply air enters the rack through the room
• 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

01/2010
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

01/2010
Summary:
• Target of all these various possibilities is the complete separation of warm
return air and cold supply air
• This separation leads to an increased temperature difference between
return and supply air temperature of the CRAC unit
• A high temperature difference increases the efficiency of the CRAC unit
and therefore the efficiency of the data-centre in general
• What kind of separation can be used in a data-centre is depending on the
situation and used equipment
• The highest level of efficiency is reached if each m³ of circulating air takes
the design amount of heat from the IT-euipment

01/2010
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, heat
density 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 !

01/2010
The leading and most important temperature
is the air entering the IT equipment (server).
According to the new ASHRAE environmental
envelope supply air temperatures up to 27°C
are possible. That would lead to return air
temperatures of approx. 37°C.
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
35°C
27°C
9. Return Air Conditions

01/2010
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 air
temperatures 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 Conditions

01/2010
10. Chilled Water System Water Conditions
Heat loads in data-centres are nearly all
sensible cooling load with only a small latent
cooling load due to fresh air ventilation.
In accordance to the increased return air
temperatures the chilled water temperatures
can be increased as well.
• Chiller efficiency will be increased due to increased evaporating temperature.
• The higher the chilled water temperature the earlier the starting temperature
of the chiller free-cooling.
• The balance between cooling capacity of the CRAC unit and chiller efficiency
has to be evaluated.

01/2010
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%
50%
60%
70%
80%
90%
100%
Airflow Absorbed Power
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Airflow Absorbed Power
1/2
Airflow
1/8
Absorbed
Power

01/2010
4x ASD1900CW at 26°C/40%
Water 10/15°C
Standby
4x 114,6 kW = 458,6 kW net sensible
Airflow: 3x 39.000 m³/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 CRAC–unit at reduced air volume the overall
fan power is greatly reduced.
Example:

01/2010
• 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 cooling
capacity 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

01/2010
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 vibration – reduced sound level
4. Long maintanance free operation due to direct drive technology
5. Scalable air flow – easy adaptation on requirements on site

01/2010
Example:
Munich airport data centre, source:
• 600 m³ data centre, 75 server cabinets arranged in 3 rows
• 5 CRAC units (4+1), each 32 kW cooling capacity
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 28°C (supply air = 22°C)
=> Due to these changes the power consumption of the CRAC units are reduced by 35%.
=> Cabinet temperatures are reduced by 4°C – extended lifetime of servers and more reliability.

Stulz datacentre cooling

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