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Cold Aisle Containment Solutions
Significantly reduce your operation costs by implementing
inexpensive Cold Aisle Containment.
Most data centers utilize HVAC systems to pump pressurized
air to maintain a server inlet temperature within the proper
temperature range (Current ASHRAE recommendations are for inlet
temperatures of 18-27 C (64.4 deg F through 80.6 deg F) and
an absolute humidity/dew point range of 5.5-15C (41.9-59 Deg
F). These CRAC/CRAH solutions usually provide air under raised
floors but above air solutions are also available.
This design struggles because it lacks precision. The HVAC
system addresses an entire room, meaning some areas receive
excess cooling, while others don't receive enough. As a result,
the entire infrastructure—from the fans, to pumps, to air handlers—must
work harder and consume more energy in the process.
Professionals facing such problems should first evaluate
their cooling architecture and determine if the capacity exists
to address existing and future compute loads. If this capacity
exists, the goal is to harness it—to focus the cool air precisely
where it's needed. Because of the prevalence of hot aisle/cold
aisle in existing data centers, one of the more practical air
management strategies is cold aisle containment.
What is Cold Aisle Containment?
Cold Aisle Containment augments its predecessor's (hot aisle/cold
aisle) arrangement by enclosing the cold aisle. The aisle then
becomes a room unto itself, sealed with barriers made of metal,
plastic, or plexiglass.
Hot Aisle/Cold Aisle Challenges:
Even at minor heat loads, there are challenges associated
with hot aisle, cold aisle. Some of them include:
- Bypass air—"the volume of cold supply air that
enters the room but does not directly enter the IT equipment"—limits
the precise delivery of cold air at the server intake.
- Hot air recirculation, where exhaust heat enters
the cold aisle, either over the tops of racks or through
open rack spaces, ensures that the cooling infrastructure
must throw colder air at the equipment to offset this mixing.
- Hot air contamination prohibits the air handlers
from receiving the warmest possible exhaust air, rendering
their operation less efficient.
- Hot spots may persist as a result of all of the
above
Diagram of a Data Center with Bypass Air problems (mixing
of hot and cold air) - a very common cause of power loss.
As rack densities inevitably climb, the challenges
above become more severe. The infrastructure struggles to deliver
a sufficient volume of cool air to the equipment and to move
exhaust air to the air handlers. As it's forced to deliver colder
air at a greater CFM, the cooling scheme consumes more energy
from the fans through the pumps, down to the chiller. And even
under minimal loads, the efficiency of these systems is suspect.
The premise of cold aisle containment, though simple, can improve
cooling performance
The Evolution of Cold Aisle Containment
Cold Aisle Containment started as a makeshift design using
the vinyl curtains common in cleanrooms and freezers. These
curtains, functioning as doors and roofs between the cold aisles,
proved an inexpensive way to increase efficiency and a simple,
flexible retrofit for most data center environments.
As more data centers embrace the concept, some
rack manufacturers are bringing their own cold aisle containment
systems to market. The barriers, instead of curtains, are fabricated
from steel and use polycarbonate inserts to provide a viewing
window into the cold aisle.
The same rack manufacturers, in new construction
or renovation projects, may promote the use of containment with
In-Row air conditioners. These units, more compact, are embedded
within the row of server racks, immediately capturing server
exhaust air, conditioning it, and distributing it to the cold
aisle.
Enhanced, Efficient Airflow Management
Due to the open architecture of the data center room, hot
aisle/cold aisle cannot attain complete air separation. With
the cold aisle encased, the cold air, delivered from under the
floor, stays where it's needed at the server intake. The roof
and walls of the containment ensure that the only place this
air can exit is through the rackmount equipment. The exhaust
air, because of the boundaries, routes back to the air handlers
only, eliminating the previous concerns of hot air contamination
and hot air recirculation.
Higher Density Installations
If there's adequate capacity in the central
plant, cold aisle containment can harness that capacity to support
higher density cabinet installations. With mixing out of the
equation, the system can focus on cooling the load instead of
the entire room. As a result, data center professionals have
a more predictable system—a consistent server inlet temperature,
within ASHRAE ranges, unaffected by the higher server exhaust
temperature.
A server cabinet manufacturer, in testing, successfully
rejected 20kW per rack with its cold aisle containment system,
using a server inlet temperature of 65 degrees, Delta T across
the servers of 45 degrees F, and 65% perforated floor tiles.
A case study at the 2008 Silicon Valley Leadership Group, entitled
Air Flow Management, advocated containment as a viable high
density solution but stopped short of giving a range of cooling
capacities.
Air Handler Efficiency and Capacity
Efficiency strategies often discuss Delta T.
The topic is especially significant with computer room air handlers
for an "elevated return temperature…to the cooling unit enables
better heat exchange across the cooling coil, better utilization
of the cooling equipment, and overall higher efficiency" (Niemann,
2008)
Cold aisle containment, through its boundaries,
ensures that server exhaust air is not unnecessarily cooled
before it returns to the air handlers. By improving the heat
exchange across the coils, the containment maximizes the capacity
of the entire air conditioner. In an existing facility with
numerous computer room air conditioners, perhaps this means
installing Variable Speed Drives (VSDs) to ensure fan speed
matches the load or even turning off unnecessary air conditioners.
As a result, the facility consumes less energy
and the organization saves money on the smaller electric bill.
Central Plant Energy Efficiency
ASHRAE recommends server inlet temperatures
between 64.4 deg F and 80.6 deg F. Chillers typically produce
chilled water around 45F degrees and inlet air around 58F degrees.
This disparity exists, again, because of air mixing within the
data center. As inlet air and exhaust air interact, the hope
is the resulting inlet temperature falls somewhere in the ASHRAE
recommended range.
Through containment, a user can eliminate this
uncertainty. If he desires a 68F degree inlet temperature, perhaps
he can achieve it with 58 degree F water. The warmer the water,
the more efficient the chiller operates.
An EYP study compares a California facility
with a 45 deg F chilled water setpoint to a 55 deg F alternative.
The test approximates an annual energy savings of over $388,000,
based on a utility rate of $0.10/kWH. This figure is both compelling
and ambiguous, for it's not practical for every data center
to simply raise their chilled water temperature. A thorough
analysis of the cooling scheme is needed, especially if the
central plant serves a mixed use facility.
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Cold Aisle Containment
Diagram
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Conclusion
On the data center floor, cold aisle containment provides targeted
cooling. This precision has many operational advantages, as
we've seen. Servers are assured a consistent inlet temperature;
air conditioners can achieve greater capacities; the chiller
plant can become more efficient by supplying and receiving elevated
water temperatures. These improvements sound great on paper,
yet they also produce tangible result: a reduction in capital
and/or operational expenses. Consider the following examples:
- A presentation at 2008's Data Center Energy Summit found
that containment could reduce fan speed in the subject data
center by 75%. Fan speed is directly proportional to fan
energy consumption (Tschudi, 2008)
- A facility in the design stages, using cold aisle containment,
may require less air conditioners, reducing the initial
capital expenditure.
- An existing facility with thermal challenges may be
able to maximize the entire cooling infrastructure through
containment, instead of undertaking a long, costly renovation
or construction project.
- Depending on the location, a facility may receive rebates
or incentives from its utility for deploying cold aisle
containment. If so, users may demonstrate a quick ROI to
their management team.
The current economic climate may delay an organization's
ability to build a new data center. As a result, they will demand
more uptime and more computing capacity from their existing
facilities, while the industry encourages conservation and sustainability.
Cold Aisle Containment proves an economical way to achieve both
objectives.
Bibliography
EYP Mission Critical Facilities. (2006, July 26). Energy
Intensive Buildings Trends and Solutions: Data Centers.
Retrieved February 2, 2009, from Critical Facilities Roundtable:
http://www.cfroundtable.org/energy/072106/myatt.pdf
Niemann, J. (2008). Hot Aisle vs. Cold Aisle Containment.
Retrieved December 23, 2008, from APC Corporate Web Site:
http://www.apcmedia.com/salestools/DBOY-7EDLE8_R0_EN.pdf
Tschudi, W. (26, June 2008). SVLG Data Center Summit-LBNL
Air Management Project. Berkeley, CA, United States of America.
About 42U
Since 1995, 42U has been a leader in providing
data center efficiency
solutions for data center and facilities managers. Our vendor and technology
agnostic approach leverages our best-practice expertise in monitoring, airflow
analysis, power, measurement, cooling, and best-of-breed efficiency technologies
to help data center managers improve energy efficiency, reducing power consumption
and subsequently lowering energy costs.
This work is licensed under a
Creative Commons Attribution-No Derivative Works 3.0
Unported License.
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