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4. Block unused rack locations with blanks Equipment typically draws in cool air
from the front and exhausts it out the back. Blanking open areas under equipment
prevents the exhaust from being drawn back into the device.
5. Design with cooling in mind Although most do, some equipment does not draw
air in from the front and exhaust it out the back. Some have top-discharge or side-
to-side designs. Configure your racks to ensure your equipment doesn’t blow into
the intake of other equipment.
6. Select racks with good airflow Buy racks that don’t have an internal structure
that would block the smooth flow of air to your equipment.
Supply Air Directly to Heat Sources
Rather than shelling out the money to cool the entire datacenter, you can save some money PART II
and just cool down the devices generating heat. These tips can help:
• Use the correct diffusers The type of diffuser you would use in an office is not
appropriate for a datacenter. Select diffusers that deliver air directly to the
equipment that needs cooling.
• Correctly place supply and returns Diffusers should be placed right by the
equipment to be cooled. They should not be placed so they direct cooling air at heat
exhausts, but rather into the air intakes. Supplies and slotted floor tiles should not
be placed near returns to prevent a cool air “short circuit.”
• Minimize air leaks Systems that use a raised floor can lose cool air through cable
accesses in hot aisles.
• Optimize air conditioner placement In large datacenters, a computational fluid
dynamics (CFD) model would be useful. This helps locate the best placement for
cooling units. It also helps minimize the distance between air conditioner units and
large loads.
• Use properly sized plenums Return plenums need to be the right size to allow a
lot of air to flow through. Obstructions such as piping, cabling trays, and electrical
conduits need to be taken into consideration when plenum space is calculated.
• Provide enough supply Under-floor supply plenums must be big enough to allow
enough air to service your equipment. Again, take into consideration obstacles such
as piping, cabling trays, and electrical conduits.

Fans
Fans also suck up a lot of power, especially when a lot of them are spinning at the same
time. Take these tips into consideration to improve fan efficiency:

• Use a low-pressure drop system Use low-pressure drop air handlers and ductwork.
Make sure there is enough capacity in your under-floor plenums to allow air to flow.
• Use redundant air handlers during normal operations It is more efficient to use
auxiliary fans at a lower speed than a single fan at high speed. Power usage drops
with the square of the velocity. As such, operating two fans at 50 percent capacity
uses less power than one fan at full capacity.