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Cold Aisle Containment
Executive Summary
This application note explains the benefits of cold aisle containment systems. The cold aisle is defined as the walkway
formed by the front of two opposing rows of IT racks. The intention of this aisle is to aid the delivery of cool air to
the inlet of the rack mounted IT equipment from an under floor air delivery supply method. Containment can
improve the predictability and reliability of the cool air delivery while saving energy.
Many products and methods exist to accomplish the benefits of containment, and these systems can be composed of
various materials and construction. All solutions have two stages of containment, which are the end of row and above
rack ceilings. This paper describes the differences in the technology of cold containment strategies, and benefits of
each stage as compared to the traditional method of under floor supply and open space return systems typically found
in data centers. Wright Line designs and manufactures cold aisle containment systems that will facilitate up flow, down
flow; rack-based and free standing demands for Wright Line and third party IT racks.
Note that deployment considerations for containment should be investigated and are not to be taken lightly.
Important issues include aisle lighting, fire detection/suppression, and egress methods for personnel. These issues will
not be covered in this application note.
Traditional Open Supply (Chaos Method)
The traditional data center employs an air distribution method that starts at the down flow air conditioner outlet.
This supply of cool air is distributed under a raised floor. The supply air is then allowed to ventilate up through
perforated tiles in the floor ideally located in the cold aisle. The IT equipment can then draw this cool air in the front
and out the rear of the IT rack. The warm air is then collected in the hot aisle and eventually returned to the air
conditioner to complete the cycle. The amount of air exiting through the cold aisle tiles is approximately 140% of that
required by the IT equipment. This oversupply is meant to ensure that all IT equipment is cooled, while creating a
cold air mass that will keep the majority of warm air away from the aisle and in turn the inlet of the IT equipment.
The oversupply distribution method is susceptible to two types of recirculation of the hot air to IT rack inlet, around
the end of the row and over the top. The oversupply method will keep this to a minimum, but as air mass, pressure,
and flow in the data center change, these dangers typically result in overheated and failing IT equipment. The
remaining 40% oversupply air that was released into the cold aisle becomes bypass air that mixes with the IT exhaust
air and returns to the air conditioner, lowering the efficiency and capability of the device to effectively cool. As a
Data center is seldom a static environment; the effects of many types of change can have a significant impact on the
performance of the open supply air distribution method. This application note highlights the end effect of change as
reduction in air flow. Some of the root causes of air flow change can be traced to under floor blockage, changes in
static pressure, removal of tiles elsewhere in the data center, and loss of air conditioner units.
Wright Line LLC
• 160 Gold Star Boulevard
• Worcester, MA 01606
800.225.7348 • Fax: 508-365-6178 • www.wrightline.com • info@wrightline.com
108
In the following figures, the unpredictability in cooling performance in this architecture is clearly apparent as a data
center changes, much like the actual dynamic environment of the common data center.
Figure 1.1
Figure 1.1 shows the front view of racks with 140% oversupply of air from under floor. The susceptible areas of
potential hot spots can be seen on both ends and upper middle section.
Figure 1.2
Figure 1.2 shows the front view of racks with125% oversupply of air as it relates to the IT demand. The previous
susceptible areas are now in the early formation of hot spots that can affect IT performance and reliability.
Figure 1.3
Figure 1.3 shows the front view of racks with 97% of air supply. Areas of the IT rack are rendered completely
unusable as hot spots progress well past acceptable limits of the IT operating environment.
Wright Line LLC
• 160 Gold Star Boulevard
• Worcester, MA 01606
800.225.7348 • Fax: 508-365-6178 • www.wrightline.com • info@wrightline.com
108
Stage 1 Containment End of Row
The Traditional data center can employ a system at the end of the cold aisle row that works as a barrier. This barrier
is typically a door designed to prevent two problems from happening. The first is the early exiting of the oversupply
cool air out the end of the rows. The second is the intrusion of the hot air into the cold aisle around the end of the
row. These functions are both beneficial and can achieve improved results over the open supply system by ensuring
the space inside the row acts like a bathtub that fills up evenly with cool air. This method evenly distributes the cool
air mass in the front of IT racks and the oversupply can only exit out the top. The warm air is then collected in the
hot aisle and eventually returned to the air conditioner to complete the cycle. Now that a significant contributor to
warm air recirculation has been eliminated, the performance of the cooling system can be more accurately predicted
when there is a change in the air flow rates to the cold aisle.
Figure 2.1
Figure 2.1 shows the front view of racks with 140% oversupply or air and End of Row doors on each end of the cold
aisle. All early indicators of hot spots have been eliminated and consistent temperature of cool air mass can be
expected to enter the rack in all unit locations.
Figure 2.2
Figure 2.2 shows the front view of racks with 125% oversupply of air and End of Row doors on each end of the cold
aisle. Depending on conditions outside the row, the exhaust heat from the row can be seen forming at the top middle
of the row and will soon be entering the IT equipment.
Wright Line LLC
• 160 Gold Star Boulevard
• Worcester, MA 01606
800.225.7348 • Fax: 508-365-6178 • www.wrightline.com • info@wrightline.com
108
Figure 2.3
Figure 2.3 shows the front view of racks with 97% of air supplied and End of row doors on each end of the cold aisle.
During an undersupply condition the exhausted heat is allowed to be pulled down into the cold aisle creating hots
spots that can degrade IT performance.
Stage 2 Total Cold Aisle Containment
A total cold aisle containment strategy typically consists of end of row doors and a ceiling system. In high
performance products the ceiling system is comprised of clear Lexan removable panels. These panels cross the aisle
just above the IT racks and are typically supported by the IT racks. In conjunction with doors, the ceiling forms a total
containment system.
In total containment, most air that enters the cold aisle goes through the IT equipment. Minor leakage can be
expected, and a reasonable amount is around 3%. This 3% is due to cover gaps, wire egress points, or fire equipment
egress. Total containment contributes an added benefit in the rise of cold aisle static pressure. This static pressure is
significantly greater than that of previous methods of an open cool air distribution. The major benefits of total
containment is the ability to closely match supply with demand and a reduction in energy consumption as the
oversupply of air is no longer used to move hot air away it is only used to provide cooling to IT equipment. This
method delivers the most predictable cooling in the dynamic environment of ever changing data centers.
Figure 2.1
Figure 3.1 shows the IT racks with 140 % over supply. Much energy is wasted in this model as the extra air is being
forced through the IT equipment and overcooling by a significant amount
Wright Line LLC
• 160 Gold Star Boulevard
• Worcester, MA 01606
800.225.7348 • Fax: 508-365-6178 • www.wrightline.com • info@wrightline.com
108
Figure 2.2
Figure 3.2 shows the IT racks with 125% oversupply, again much energy is wasted as the IT equipment is experiencing
additional air that is not required, no hot spots
Figure 3.3
Figure 3.3 shows the IT racks with 97% air supply, performance of the cold aisle system is highlighted as an
undersupply condition is starving the IT equipment of air yet maintaining a high level of cooling performance while
closely matching supply with demand.
Conclusion
Cold aisle containment systems can provide a data center with better cooling performance as well as improved
cooling efficiency in new or existing facilities. Many factors will lead to an implementation decision for a particular
stage of containment or product selection. However, the benefits will remain consistent with end of row and ceiling
systems. The increased performance in your cooling system can now be tuned toward supporting additional load or
improving the energy consumption of the facility.
Wright Line LLC
• 160 Gold Star Boulevard
• Worcester, MA 01606
800.225.7348 • Fax: 508-365-6178 • www.wrightline.com • info@wrightline.com