AIT Partnership Group Ltd
White Paper: Using Cold
Aisle Containment in the
Data Centre
Retrofitting cold aisle containment to increase capacity and reduce energy use
Tim Daniels
14/10/2013
White Paper: Using Cold Aisle Containment in the Data Centre
October 14, 2013
Retrofitting cold aisle containment to increase capacity and reduce energy use
Contents
1.
Summary ......................................................................................................................................... 2
2.
Traditional Approaches to Data Centre layout ............................................................................... 3
3.
Cold Aisle Containment................................................................................................................... 4
4.
Design of Cold Aisle Containment................................................................................................... 5
a.
Fire Detection and Suppression .................................................................................................. 5
b.
Hot Aisle Containment ................................................................................................................ 5
5.
Maximising Efficiency...................................................................................................................... 6
6.
Examples of Best Practice ............................................................................................................... 7
7.
a.
Case Study 1: The University of Nottingham (Hot Aisle Containment Example)........................ 7
b.
Case Study 2: DIY Chain (Cold Aisle Containment Example) ...................................................... 8
References ...................................................................................................................................... 9
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White Paper: Using Cold Aisle Containment in the Data Centre
October 14, 2013
Retrofitting cold aisle containment to increase capacity and reduce energy use
1. Summary
Our ever increasing use and dependency on corporate and cloud software applications
mean that data centres, which house the computing and storage equipment on which all
this software runs, are continuously under growth pressure. As a consequence data centres
use a large and growing amount of energy both to run the IT equipment and to cool it.
The overwhelming majority of data centres rely on air-based cooling provided by airconditioning to keep IT equipment in the server racks below the industry standard
temperature limit of 27⁰ C. In order to achieve this air temperature is closely monitored and
controlled within the data centre. IT equipment running too hot will reduce its lifetime and
cause early failure, while over cooling the data centre wastes energy and increases costs.
A traditional style commonly used in building data centres has been to use an open-plan
room, with cold air fed to the server racks via an under floor void and warm air re-circulated
from the server racks back to the air-conditioning units at ceiling level. Some mixing of the
warm and cold air flows used to be tolerated but cold aisle containment overcomes this
problem.
Cold aisle (or hot aisle) containment stops cool air mixing with warm air, typically reducing
data centre energy costs by 10-20%. Examples of both cold aisle and hot aisle containment
are provided in this white paper. One large UK DIY chain, reduced their cooling costs by 14%
by introducing cold aisle containment in its data centre. It should be noted that this data
centre was already well organised, and managed. Studies have shown that if data centres
are badly configured then rearranging the cabinets, air flow and air conditioning systems,
and improving their management, can reduce energy consumption by over 50%.
Ref 1: Example of Cold Aisle Containment
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White Paper: Using Cold Aisle Containment in the Data Centre
October 14, 2013
Retrofitting cold aisle containment to increase capacity and reduce energy use
2. Traditional Approaches to Data Centre layout
Early data centres and IT equipment rooms were traditionally located within a building with
little planning for airflow and equipment cooling. Equipment was placed into rows of
standard sized 19 inch wide server racks. Brute force cooling methodologies were used to
cool the room, usually with air-conditioning units placed around the periphery of the room,
positioned along the ends of the rows to let the cool air flow along the rows. Hot spots tended
to occur in heavily loaded racks in mid-aisle positions which were furthest away from the airconditioning. Overcooling some areas, along with powerful ventilation, was a necessary
(costly) evil in order to avoid hot spots.
During the 1990s raised flooring became widespread in commercial building design which
gave great flexibility to office layout, allowing services to run under in an under-floor plenum
(space) to any part of the room. Data centres used this concept too, delivering cold air via an
under floor plenum space to specific ‘cold’ aisles in the data centre. These cold aisles are
arranged with cabinet fronts on both sides of the aisle. The alternate rows, known as ‘hot’
aisles, receive hot air from the rear of the server cabinets on both sides.
Hugely practical, the concept of hot and cold aisles with an under floor plenum was widely
adopted by the industry and has served well for many years. Properly balanced, the cold air
coming from the under floor plenum naturally creates a positive pressure in the cold aisle that
flows into and over the server cabinets towards the hot aisle. Hotter air rises and flows back to
the air-conditioning units creating a natural air circulation system within the data centre.
Ref 2: Traditional Hot and Cold Aisle Concept
However high-density compute servers and server ‘blades’ have replaced older equipment
in-rack power usage has crept up from 1-2kW to towards 5-8kW per rack. Cooling needs have
also grown in proportion with this increased power making it ever harder to keep servers
within ASHRAE temperature limits.
The challenge for data centres is that they are designed to last for many years, even
decades, and yet the equipment within them changes every 3-5 years. The need to improve
cooling effectiveness has become a key factor in order to cram in more high-density
compute servers. More efficient cooling will also allow tighter temperature regulation,
improved reliability, longer equipment life, lower running costs, and a reduced carbon
footprint to comply with government initiatives.
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White Paper: Using Cold Aisle Containment in the Data Centre
October 14, 2013
Retrofitting cold aisle containment to increase capacity and reduce energy use
3. Cold Aisle Containment
For traditionally designed data centres the introduction of physical separation between the
hot and cold aisles eliminates the mixing of hot and cold air streams, and instantly improves
thermal efficiency. Separating the air flows improves server rack cooling and enables higher
in-rack equipment densities.
There are two main ways of separating the air; the first is to flood the room with cold air and
contain the hot exhaust air, feeding this directly back to the air-conditioning systems; the
second is to contain the cold air within the cold aisle (fed via an under-floor plenum) and
allow the exhaust air to flow freely from the rear of the servers back to the air-conditioning
systems.
Some papers argue that hot air containment is more efficient but there is no universally
proven right or wrong approach. The ‘right’ approach really depends on how the data centre
has been physically designed. ‘Chimney’s’ fitted to the rear of the server cabinets can work
well to contain the hot air and feed it back to the air conditioning systems, but is often difficult
and expensive to retrofit to a live data centre. Since most data centres already feed cold air
directly to the cold aisles via an under-floor plenum it is usually simpler and cheaper to
enclose the cold aisles with roof panels and sliding doors to the end of each aisle.
Ref 3: Cold Aisle Containment
Using cold aisle containment has several benefits. Stopping the air mixing allows air
temperatures to be more closely controlled at point of delivery, and therefore raised, which
reduces energy costs. Increased operational temperatures can save even more when
coupled with free cooling systems, since external air can be used for a greater percentage of
the year due to higher set-point temperatures. Creating physical separation reduces the need
to pressurise the cold aisle to eliminate warm air re-flow, reducing the power used by the airconditioning fans. As well as saving energy costs, equipment reliability also improves because
temperatures remain more stable and this further reduces overall operational costs and
downtime.
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White Paper: Using Cold Aisle Containment in the Data Centre
October 14, 2013
Retrofitting cold aisle containment to increase capacity and reduce energy use
4. Design of Cold Aisle Containment
Cold aisle containment is simply a barrier between the cold and hot aisles. This is achieved in
various ways depending on current data centre design, efficiency needs, and the budget
available.
The simplest scenario is the use of plastic strip curtains (also known as butchers curtains) over
the cabinet rows to separate hot and cold aisles. However they tend to be ill fitting and blow
about in the breeze, creating a poor fit and reducing efficiency of the separation system.
Ref 4: Components of Cold Aisle Containment
A better solution is to fit light weight roof panels over the cold aisle and sliding doors at both
ends of each cold aisle. Usually constructed of sheet metalwork, solutions can also include
bespoke side panels to even up cabinet heights or fill in gaps where cabinets are missing. AIT
uses a variety of solutions depending on project need.
a. Fire Detection and Suppression
The roof panels are usually hinged in order to allow them to open in event of fire, allowing
existing fire detection and suppression systems to work effectively. In rare circumstances
additional fire detection and suppression equipment is needed. Many variations of
detection/suppression exist but suffice it to say we have always been able to find a practical
solution to meet the customers’ (and regulatory) needs.
b. Hot Aisle Containment
We have concentrated on cold aisle containment in this white paper, but it is equally valid to
install hot aisle containment to separate the cold and hot air. Many of the same principles
apply. The choice of which to use is dictated by the current data centre layout. Hot aisles may
be contained or chimney systems may be fitted to the rear of the cabinets to capture warm
exhaust air. A hot aisle containment case study is given the section covering examples of best
practice.
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White Paper: Using Cold Aisle Containment in the Data Centre
October 14, 2013
Retrofitting cold aisle containment to increase capacity and reduce energy use
5. Maximising Efficiency
Installing cold aisle containment, by design, changes the air-flow characteristics of the data
centre. To maximise those benefits it is important to perform a data centre audit before
installing the containment to highlight and plan for any other changes that must be done in
conjunction with it.
Since the cold air flow is now contained the fans within the computer room air-conditioning
(CRAC) must often be adjusted to reduce air flow. Additional savings can often be made by
updating the CRAC with new variable speed fan drives.
Temperature set-points within the CRACs must also be adjusted to suit the new conditions,
usually to increase the temperatures. ASHRAE now recommends data centre running
temperatures up to 27⁰C, yet many still run in the 18-21⁰C range. More controlled air flows
mean higher temperatures can be maintained without the danger of hot spots occurring.
Sometimes the number of CRACs and their cycling order must also be adjusted for the new
setup.
The data centre may also want to retrofit measurement equipment to measure power use
within the data centre at the CRAC and server-rack level (or distribution board), and measure
temperature at various points within the cold and hot aisles. Since each cold aisle becomes
enclosed, closer monitoring may be necessary than has previously been the case.
An audit will also uncover under-floor plenum issues, such as reduced air flow due to cable
stuffing, and recommend any floor vent re-configuration to maximise efficiency after
installation of the cold aisle containment system.
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White Paper: Using Cold Aisle Containment in the Data Centre
October 14, 2013
Retrofitting cold aisle containment to increase capacity and reduce energy use
6. Examples of Best Practice
AIT Partnership Group has installed many cold aisle containment systems in the UK, within
large data centres and smaller IT equipment rooms, for businesses and public sector
organisations.
a. Case Study 1: The University of Nottingham
(Hot Aisle Containment Example)
An AIT data centre audit uncovered efficiency savings that would save them an estimated
£5,808 a year. Hot aisle containment (rather than cold) was installed as part of the solution
due to the configuration of the data centre. The payback period for the project was
estimated to be less than three years, while their efficiency rating improved from a PUE of 1.8
to a PUE of 1.5. (PUE = power usage effectiveness ratio). Chris Tadman, the data centre team
leader at The University of Nottingham was very happy with his new hot aisle containment. “I
estimate the hot aisle containment system made a 5% saving on our Primary Data Centre
energy usage. It helps us to meet the expanding computing requirements of the University
whilst reducing our energy bill and Carbon Footprint, both of which are very important targets
for the University.”
Read the full University of Nottingham Case Study
Ref 5: One aisle of containment showing sliding door
and bespoke side panels to create an airtight aisle.
Ref 6: Bespoke doors to allow access to contained aisle.
Ref 7: Another view of bespoke doors and metalwork to
create the aisle containment chamber.
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White Paper: Using Cold Aisle Containment in the Data Centre
October 14, 2013
Retrofitting cold aisle containment to increase capacity and reduce energy use
b. Case Study 2: DIY Chain
(Cold Aisle Containment Example)
AIT recommended and installed cold aisle containment in the data centre of Europe’s
leading DIY chain. The effect was instant, a 4⁰C drop in temperature within the cold aisle.
Once balancing and reconfiguration of the CRACs took place it was estimated that the
customer would save nearly £40,000 per year, paying for the project in very little time.
Read the full DIY Chain Case Study
Ref 8: Data Centre hall with aisles on either side. Each
aisle has cold aisle containment with a sliding door on
each end.
Ref 9: Inside each aisle, with the server rack fronts on
both sides and cold aisle containment roof overhead
Ref 10: On odd shaped aisle with in-filling panels on
one side to create an airtight space. These can be
removed and replaced with cabinets as the data
centre expands.
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White Paper: Using Cold Aisle Containment in the Data Centre
October 14, 2013
Retrofitting cold aisle containment to increase capacity and reduce energy use
7. References
Focused Cooling Using Cold Aisle Containment (Emerson)
http://www.emersonnetworkpower.com/documents/enus/brands/liebert/documents/white%20papers/focused%20cooling%20using%20cold%20aisl
e%20containment.pdf
Hot Aisle vs Cold Aisle Containment (APC)
http://www.apcmedia.com/salestools/DBOY-7EDLE8_R0_EN.pdf
Cold Aisle Containment for Improved Data Center Cooling Efficiency (Rittal White Paper 506)
http://www.rittal.us/literature/download.cfm?id=554&sbu=05
AIT Hot and Cold Aisle Containment
http://www.ait-pg.co.uk/data-centre-management/data-centre-design-and-build/hot-coldaisle-containment/
AIT Partnership Group Ltd
1 Southern Court
South Street
Reading
RG1 4QS
0845 293 2970
www.ait-pg.co.uk
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Group Ltd. All other company or product names may be trademarks or registered
trademarks of their respective owners.
Whilst every effort has been made to ensure accuracy, neither the author nor AIT takes
responsibility for the information given herein.
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