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C h a p t e r 4 : h a p t e r 4 :

Something you’ll notice about Figure 4-4 is that the cool sides of equipment are
arranged together, whereas the hot sides of equipment face each other. This allows the
equipment to draw in cool air, rather than air that has already been preheated by the rack of
equipment in front of it.
The cold aisles have perforated floor tiles to draw cooler air from the raised floor. Floor-
mounted cooling is placed at the end of hot aisles, but not parallel to the row of racks. This
is because parallel placement can cause the hot exhaust to be drawn across the top of the
racks and mixed with the cool air. It also decreases overall energy efficiency.

Raised Floors
Datacenters are conventionally built on a floor that is raised 18 to 36 inches. The higher the
floor level, the more air that can be distributed under the floor and the more air that can be PART II
used by the cooling system.
But higher isn’t always practical. There can be major disruptions to day-to-day
operations. Plus, the higher up you build the floor, obviously, the closer you’ll be getting to
the ceiling. This can be a hindrance not only for rack sizes, but also for the flow of air over
the top of equipment.

NOTE Too much can be too much. To accommodate the cooling needs of 400 watts per square foot,
the floor would have to be elevated 5 feet. You can only count on so much from your raised floor
before you need to consider supplemental cooling options.

Cable Management
Developing a good cable management system in conjunction with the hot-aisle/cold-aisle
design can equate to more energy efficiency.
Whenever possible, it’s best to route your cables under the hot aisle, as shown in
Figure 4-5. This reduces the cool air’s path to the equipment as it is drawn in through
the perforated tiles and into the equipments’ cooling systems.

Hot aisle Cool aisle

Exhaust Air intakes

Cable should be routed
under the hot aisle

FIGURE 4-5 Route cables along the hot aisle whenever possible to avoid airflow problems in the
cool aisle.