Air conditioning Close control
or carbon dioxide, and the key to specifying the right
one is to keep it simple and offer best value: “Match the
cooling medium to the equipment loads/rack density,
while capturing the client’s attitude to risk of water in
the data centre.”
Air has long been the engineer’s preferred cooling
medium, but it is limited to around 7kW per cabinet
depending on cabinet layout, space constraints and
airflow strategy. Water is more efficient at cooling
computers than air. However, water is a conductor of
electricity, and IT operators can be deterred from using
a solution that involves a water-electronics mix.
Hutchins maintains that carbon dioxide, on the other
hand, is a perfect cooling medium for IT applications
because of its key properties. It is, he says, ironic that
the very substance responsible for contributing to the
destruction of the planet could also be its saviour, or at
least be a potent weapon in the battle against climate
change.
“CO2 is a significant greenhouse gas and a big
It is ironic that the very substance responsible for
contributor to global warming. However, using CO2
contributing to the destruction of the planet could also
as a coolant for computer systems can help save energy
be its saviour, or at least be a potent weapon in the
and, therefore, reduce the carbon emissions that
increase the likelihood of global warming,” Hutchins
battle against climate change
says.
This, he argues, is a compelling argument in favour
> consider how to get that heat out of the building, of CO2 as an energy-saving alternative to air or water.
too. If it is a chilled water system, for example, you TROX AITCS believes that, ultimately, CO2 will
might have a free-cooling chiller. This means that, dominate the high and super-high density sectors.
on days when there is a low ambient temperature, “However,” adds Hutchins, “in the current financial
the cooling can be provided by a direct air-to-water climate, where capital cost is king, we are offering
exchange without running any energy-consuming low-energy, scalable solutions that enable low-density
compressors. systems to be upgraded to medium and high on a rack-
“So, don’t just think about getting the heat out by-rack basis.”
of the server efficiently, or the heat out of the room Whichever close control air conditioning system
efficiently; think also about getting the heat out of the is specified by a consultant, it is crucial to follow
building efficiently. After all, it doesn’t matter if you one cardinal rule: don’t take chances – ensure your
have an efficient close control unit if you attach it to system choice maintains the integrity and resilience
an antiquated chiller.” of the computer/data centre. There can, after all, be no
There are, says TROX AITCS sales director Guy compromise in terms of the availability of this mission-
Hutchins, essentially three cooling media to cool the critical equipment; if it fails, people’s livelihoods are
IT equipment that produces high heat loads – air, water on the line. l
Systems: Computers get cooling treatment
There are three main types of close control to the high-density load. Finally, there are technology will happen when the cooling
system for computers – rack cooling, more conventional close control perimeter medium cools the chip directly. However, the
close-coupled systems and conventional units that can be attached to, for example, company does not foresee this happening
close control perimeter units – according to a cold aisle containment system that is soon because of the higher costs involved
supplier Emerson Network Power. capped to ensure that cold air brought in for for the user.
With rack cooling, the rack in which the cooling does not mix with hot air leaving the Supplier TROX AITCS categorises
IT server sits is cooled directly by a built- system. equipment racks in the following way:
in, close-control air conditioning system. The vast majority of servers are cooled by
Regardless of the cooling medium, most pulling air through them via a fan rather than
Rack density kW per rack Medium
racks are air-cooled. cooling the microprocessor chips directly.
Low density 1– 7kW Air
Second, there are close-coupled systems. The air itself can be cooled in a number
Medium density 8 – 14kW Air / CHW / CO2
These involve putting cooling systems either of ways – for example, via chilled water, High density 15 – 24kW CHW / CO2
in between, on top of, or above the racks; so refrigerants or carbon dioxide. Super high density 25+kW CO2
you are adding additional cooling directly According to Emerson, the leap in
CHW = chilled water
52 CIBSE Journal March 2009 www.cibsejournal.com
CIBSEmar09 pp50-53 control.indd 52 4/3/09 14:48:43
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