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Modular Cooling for
High Heat Density Racks

Richard Garafola
Senior Director – Sustainable Power Solutions

Agenda

 Market drivers: why look at cooling technology

 A review of and issues with present cooling technology

 Our approach

 Our design

 Case study

 Business case approach

2 | Modular Cooling for High Heat Density Racks | March 2010 All Rights Reserved © Alcatel-Lucent 2010, CMO7526100204

Typical data center power consumption profile

Area of Interest

In addition to real savings to the environment, even modest advantages
in router energy efficiency add up to significant savings in OPEX costs


Heat transport paths in a typical CRAC-cooled data/IP center
From source (cabinet/frame/rack) to external environment:

―Waste heat‖

Issues created by CRAC-based cooling
• CRAC units use a lot of energy, compared to the heat they remove.
• Cool air mixes with warm air before entering the cabinet - increasing the air
temperature used in cooling and decreasing its effectiveness.
• Warm air mixes with cold air before returning to the CRAC unit – decreasing the
efficiency of the CRAC unit.
• Addressing ―hot spots‖ or focused cooling is hard to achieve, leading to overcooling
and poor utilization of space.


Space issues in a typical data center:

Space utilization/thermal density:
Current configuration significantly limited by thermal load
Air conditioning-based cooling has an upper limit of heat density per
cabinet
Empty enclosures • No empty racks
• New servers

Server’s

Current configuration using conventional CRAC cooling Possible configuration if
greater cabinet heat densities
were obtainable
Results:
• Poor utilization of expensive data center space ($200 to $800 per square foot)
• Using (lighting, cooling, paying for) more space than required
• Expanding data centers when the existing space may be adequate
• Purchasing more cabinets than necessary


Modular cooling solution - heat transport paths using pumped
refrigerant from source (cabinet/frame/rack) to external environment:

Pump unit Two-phase Refrigerant
Low maintenance –
transfers heat refrigerant is supplied to the
requires only periodic
from refrigerant returned to the cooling units in a
inspections
to building chilled pump unit liquid state
water

Cooling
modules grow
with your
system

Building chilled water
Low pressure (55 psi, 3.8 bar) pumped
(XDP pump)
refrigerant supplied to each cabinet Phase change occurs within
micro-channel evaporators,
removing heat from the server
exhaust air

Use refrigerant-based heat exchangers to transfer heat into a coolant
at the source of the heat and pipe to outside of local environment

MCU rear access

• MCU is double hinged, allowing for rear access to servers.
• The fan and coil sub-assembly can be removed by activating
spring plungers and disconnecting quick connect hoses.
• The unit can be removed without turning off the system or
evacuating the refrigerant
• No tools are required to gain access.

Easy access

MCU with door

Server- and cabinet-agnostic
• Three MCUs per rack with door installed – two
different cabinet styles

Doors remain

Modular Cooling Solution primary benefits

• More efficient: up to 90 percent!

• Eliminates condensation on refrigerant distribution system

• Improved real estate utilization

• Retrofit: without down time and without redesign

• Eliminates ―over-cooling‖

• Reduces office air handler/blower requirements (less air conditioning units)

• Avoids bringing water close to electronics

• Helps meet eco-environmental initiatives


Modular Cooling Solution – Alcatel-Lucent IPTV Lab (Plano, Texas, US)

17 cabinets
110 KW total heat (6.5 KW/cabinet)

Plano IPTV Lab temperatures

Isle TempBefore/ After 90/76
Server Internal Temp After 76 77 77 76 72
N/A
Server Internal Temp Before 71 82 89 91 90

Rack ID Wall 107.32 107.33 107.34 107.35 107.36 107.37

Isle TempBefore/After (rear) 104/72

Rack ID 107.21 107.22 107.23 107.24 107.25 107.26 107.27 107.28 107.29 107.30 107.31

Server Internal Temp Before 71 72 72 74 70 70 74 71 n/a 75
Server Internal Temp After 73 72 73 72 70 67 73 72 71 68 N/A

• Temperature readings taken before the upgrade included having air handlers, air returns and forced air under the floor all active.
• Temperature readings taken after the upgrade included having air handlers, air returns and forced air under the floor all TURNED OFF.

Rack Configuration Details
Rack ID 107.21 107.22 107.23 107.24 107.25 107.26 107.27 107.28 107.29 107.30 107.31 107.32 107.33 107.34 107.35 107.36
Max Before 79 77 79 81 81 72 77 73 79 84 91 97 97 95
Max After 75 73 77 75 77 72 75 75 75 75 77 79 81 81 79
Average Before 71 72 72 74 70 70 74 71 75 71 82 89 91 90
Average After 73 72 73 72 70 67 73 72 71 68 72 76 77 77 76
Min Before 66 70 70 70 57 64 61 64 72 57 68 68 73 84
N/A
Min After 70 72 70 68 63 59 72 68 59 57 63 68 70 72 72

Servers Monitored 19 19 14 14 13 14 14 12 25 20 18 17 18 11
Number Servers 30 30 21 21 19 17 22 17 26 26 20 20 20 20
Number Disk Arrays 0 0 4 4 4 4 2 3 0 0 2 2 3 3

Extremely effective

Coefficient of Performance (COP) and
savings based on efficiency

To create a business case — consider the total heat to be cooled,
the cost of each system and the cost of energy

Total heat load (KW)
Number of systems =
Sensible cooling capacity (KW)

Operating cost A ($) = Number of systems A x power consumption A KW x 8760 Hr/Yr x $ / KW Hr
Operating cost B ($) = Number of systems B x power consumption B KW x 8760 Hr/Yr x $ / KW Hr

Cost of system B ($) – Cost of system A ($)
Payback =
Operating cost B ($) - Operating cost A ($)


Example business case: pricing and cost savings

Pricing is based on:
• The number of cabinets
• The heat load per cabinet
• The resulting number of pumps
• The resulting length and amount of piping and manifolds
Example: Retrofit of existing cooling system CRAC units — savings is based on energy reduction
only (space utilization not considered)

Size of the Data Center: 22,000 sq. ft. CRAC Unit Stats: Uses 11.7 KW
Average Heat Load per cabinet: 3KW Removes Roughly 47 KW of heat.
Number of Server Cabinets: 500 Units Required: 32
Total Heat Load: 1500 KW Our Solution Stats: Uses 2KW
Removes Rougly 150 KW of heat
Total Energy Savings: 3587200 KW hrs Units Required 10
Total Energy Savings: $311,758, based on $0.10 / KW hr

Price, including installation, for this system would be $1,040,000
Resulting in a 3.3 year simple payback

Note: A new build example including the cost of CRAC units pays for itself immediately


Conclusion

• Present air-based cooling methods are inefficient.
• By targeting the heat at the source, energy and space utilization can be
improved.
• Utilizing thoughtful design avoids spending money on new cabinets, or even
moving the cabinets used today.
• Modular cooling creates a positive business case, which is further improved
when you consider the improvement in real estate utilization.


www.alcatel-lucent.com


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