green IT
It is calculated by dividing the total
power consumption by the power
consumption of just the IT equipment.
Unfortunately, the PUE metric
does not reward reductions in IT
power. Since IT power is in the
calculation’s denominator, even
though IT energy consumption
reduction is a direct and compounded
benefit, it may actually increase the
PUE value for a data centre. This
should not discourage data centre
and facility managers from pursuing
these valuable ways to reduce energy
and expenses.
Minimise cooling fan power
The next biggest energy savings
opportunity is the power consumed
by HVAC fans to move air in the
data centre. IT equipment are
virtually all air cooled devices. A
cool air supply is needed to meet
the demands of the IT equipment,
and warmed air exhausted by that
equipment needs to be removed.
Airflow optimisation requires
recognition that these two airflow
volumes are actually the same.
To minimise the amount of air
that needs to be delivered, the
mixing of cool supply air and warm
exhaust air needs to be prevented.
Data centre physical infrastructure
deployment has evolved to do this.
Hot aisle/cold aisle arrangements
of IT equipment were an early step.
Without airflow barriers however,
air mixing at row ends and over the
tops of rows still occurs, requiring
as much as 20 per cent oversupply
of cool air to offset this mixing.
Efficient airflow management
requires a containment methodology.
Fully enclosed aisles, with endof-row doors and ceilings or other
structures to contain the tops of the
aisles are effective. These are known
Cold aisle containment – with hot exhaust chimneys can mitigate cold air oversupply.
as either cold aisle containment or
hot aisle containment, depending
on whether the IT inlet or exhaust
rows are contained. Vertical exhaust
ducts, or chimneys, on IT cabinets
are another technique for containing
the IT exhaust airflow. Most new data
centres are deploying a containment
system. Existing operations can
consider ways that containment can
be added, potentially with minimal
disruption to operations.
Deploying a physical air
containment method is not the end
of the optimisation process. Data
centres are not homogeneous, static
environments. Airflow demands are
not uniform and they aren’t constant.
It is likely that some rows, regions, or
cabinets will have higher than average
demand. True airflow optimisation
requires information about the
airflow requirements and adjustment
of the flow volumes to meet the
demand without over or undersupply.
Commissioning for initial demands
is a starting point, but environmental
monitoring of air temperatures and
pressures can be used to either
recommission periodically or to
automate airflow delivery to adjust
dynamically as IT needs change.
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