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66

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