Cooling
Figure 1: Direct
free cooling.
inlet temperature and server exit
temperature are well known to
have a significant effect on the
efficiency of any cooling system
and the higher the former, the
more efficient a cooling system
can become.
Although the concept
behind free cooling is relatively
straightforward, there are a
number of ways to go about
achieving it.
Direct free cooling
metric – the closer it is to 1.0 then
the better the facility is doing in
managing its use of non-computing
energy – and free cooling can help
lower this figure.
So what do we mean by
the term free cooling? Gartner
defines it as ‘any technique used
to reduce the energy consumed
by cooling systems or the time
that the cooling units run by using
the outside temperature of air or
water to cool the data centre or
other facilities’. Free cooling helps
save energy and for most of the
time UK ambient air temperature
is colder than that required in
the data centre – so a simple
ventilation system can maintain
compliant conditions.
Figure 2: Indirect
free cooling with
air/air plate heat
exchanger.
With direct free cooling, filtered
outside air is fed directly into the
data centre if the CRAC system
determines that it is at the
right temperature. This means
that the compressors do not
have to operate as often, saving
electrical energy.
However, in urban areas air
quality might not be good enough
and is often full of particles,
which can be very hostile to
modern IT equipment. Therefore,
Temperature gauge
Before looking at free cooling in
greater depth, it is worth noting
that there are various measurable
temperatures present in a data
centre including supply air, return
air, room air, cold aisle, and server
inlet and exit temperatures. Server
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