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Rooms with a CCF
greater than 3.0
have great potential for improvement
since the total rated cooling capacity
of running units is at least three times
110% of the IT load.
THE COMMONALITY
OF OVERLOOKED AFM
IMPROVEMENTS
As the industry evolves, data center
managers are challenged by ever-
increasing IT equipment densities, and
pressured to reduce operating
expenses. Often, managers turn to
advanced AFM solutions such as full
containment. However, in many
circumstances the expectations of
these efforts are unmet because AFM
fundamentals have been overlooked.
Even if expectations are met, the full
benefits of these solutions will not be
realized unless basic AFM practices
are addressed as well.
Figure 1
shows a dramatic difference
in the intake temperatures of IT
equipment located in the bottom of
cabinets versus the top in a fully-
contained cold aisle. This is the result
of an insufficient volume of
conditioned air being delivered to the
contained space due to unsealed
cable openings throughout the raised
floor. Compounding this, the
contained aisle has open spaces
between IT equipment in the cabinets
that allowed conditioned air to flow
out of the space and exhaust air to
flow in. As a result, even though cold-
aisle containment had been installed
and the site had a CCF of 3.8 (380%
more rated cooling capacity than heat
load), IT equipment intake
temperatures were not improved. A
more cost-effective solution would
have been to address AFM
fundamentals throughout the site.
Another solution that is often
inappropriately incorporated into
computer rooms is fan-assisted
perforated tiles, which are meant to
address an insufficient volume of
conditioned air to cool adjacent IT
equipment. While fan-assisted tiles
deliver more conditioned air, they do
so at the cost of reducing the
conditioned air flow rate coming out
of perforated tiles in the surrounding
area and increasing the electrical load
in the room. In most cases, simply
sealing unmanaged openings in the
raised floor will enable existing
perforated tiles to produce sufficient
volumes of conditioned air. This
solution has other benefits, such as
increasing conditioned air volumes
through all perforated tiles in the
room, reducing or eliminating hot
spots, and enabling the raising of
cooling unit set-points. Calculating a
room’s CCF quickly identifies the
potential for solving cooling problems.
Obviously, there are appropriate
applications and benefits of fan-
assisted tiles: when raised floor
heights and/or obstructions limit
conditioned air volume in an area of a
room, or high-density cabinets require
more cooling than standard perforated
tiles or grates can deliver.
The profound insights that can result
from calculating a site’s CCF and
making fundamental AFM
improvements is shown in the
following case study of a 9,000-sq. ft.
computer room.
The room had 170 cabinets drawing a
total load of 240 kW and was cooled
by seven cooling units, six rated at 70
kW each and one at 85 kW. Electricity
cost is $0.10/kWh. As is often the
case, the site manager was struggling
to maintain appropriate IT equipment
intake air temperatures even though
the computer room CCF was 2.2. In
other words, the running cooling
capacity was 220% of the room’s heat
load, indicating that the site’s cooling
challenges were due to poor AFM and
not insufficient cooling capacity.
To “right-size” the cooling
infrastructure, simple improvements
were made to the room, including:
• Sealing cable openings
• Installing blanking panels
• Adjusting both the number and
location of perforated tiles
• Adjusting the position of a few
cabinets
• Sealing spaces where cabinets were
missing in a row
By making these low-cost
improvements, we were able to
eliminate all IT equipment hot spots
and allowed for two cooling units to
be turned off, which resulted in a
savings of $21,900 per year and a
payback period of less than eight
months.
REMEDIATION
IMPROVING COOLING
CAPACITY FACTOR
Calculating the CCF for a computer
room reveals excess cooling capacity
and opportunity for improvement.
Following a practical, impactful, and
cost-effective sequence of AFM
initiatives that start with the raised
floor, then move to the rack and
eventually the row will save both time
and effort and ensure that the full
benefits of each effort are realized.
After implementing AFM
improvements, changes at the room
level need to be made to reduce
operating costs and improve efficiency.
After each significant adjustment to
the cooling infrastructure the CCF
should be recalculated to check
progress towards the CCF goal. As
more improvements are made, this
cycle needs to be repeated.
7X24 MAGAZINE SPRING 2015
Figure 1