End User Focus
that are hot - actually this can be a
good thing - provided that these are
not located in front of cabinets. Hot
spots in front of cabinets are bad as
this means that the equipment will be
drawing in hot air, reducing the cooling
efficiency.
Hot spots in front of cabinets generally
mean that the rack layout is poor with
cabinet backs facing cabinet fronts.
Look to implement hot and cold aisle
separation.
Resist the temptation to place open
tiles in hot aisles, the “advice” that this
lift the hot air up so that it extracts
efficiently is utter nonsense and should
be ignored. Hot aisles are designed to past the equipment it is supposed to
be hot and are less efficient if they have cool. Blocking off open gaps in The delta in temperature between the
open tiles in them. Don’t worry about cabinets with blanking plates is key as air inside the curtained off area and that
the humans; they can survive high is fitting empty (and fully blanked) outside is quite dramatic, being in the
exhaust temperatures for long periods. cabinets into gaps or alternatively filling range of 10° to 15° Celsius.
full-length curtains in gaps. Refrigeration efficiency is increased by
Poor airflow from open tiles can be approximately 20%.
caused by a number of problems. Too The photograph above was taken in
many open tiles reducing the plenum BT’s Rochdale Data Centre. It shows Installing curtains and organising
pressure overall, blocked underflow the use of curtains to separate the hot cabinets and open floor tiles in a
caused by overflowing cable trays or and cold aisles, thereby reducing the sensible way is something that
stored junk. Badly maintained amount of hot air that mixes with cold everyone can do regardless of the age
refrigeration units or blocked filters can air from the plenum floor and and condition of their data centre site.
reduce airflow as well reducing plenum dramatically increasing cooling If the site is constrained by cooling
pressure. efficiency. Inside the curtained off capacity, the installation of curtains will
space are all of the open vents from the allow more equipment to be installed.
If designing a new hall, keep the cable plenum floor and all of the cabinet As a minimum the energy bills will drop
trays above ground, it can make a huge fronts. There are no open tiles in the markedly. An important fact is that
difference and is much easier to hot aisles. using fresh air to cool computer
manage. The photograph below is from equipment is more common than you
the iNet Data Centre in Milan and In combination with the curtains, each would think. I have examples of where
shows a great arrangement. cabinet is fitted with blanking plates to this is commonplace:
If you really need to have high density ensure that the only path for cold air to
equipment in a hall you might consider pass is via a piece of equipment. Many vendors expect their equipment
hot aisle containment so that you can Missing cabinets and missing to be used in office environments
exhaust the air from that equipment equipment offers an alternative route without raised floors and dedicated air
straight out to the atmosphere, bringing for airflow that causes hot and cold air handling units. There are hundreds of
in fresh air to replace. An example is to mix reducing air handling efficiency. thousands of small companies who
shown below. have a few servers installed in a
Maintaining strong separation between If you can’t fit blanking plates - move cupboard or in the corner of the office,
hot and cold aisles is particularly the equipment to the bottom of the all running at ambient temperature. The
important. Even when implementing cabinet, remember it is hot air that rises big difference between equipment
hot aisle and cold aisle separation, and the air is likely to be cooler at the located in an office space and in a
about 40% of the cold air short circuits bottom of a rack than at the top. dedicated data centre is packing
September 2008 www.datacentresols.com | DATA CENTRE SOLUTIONS | 25
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