MONTH IN FM
OCTOBER 2019 51
FMJ.CO.UK
TWO FUNDAMENTAL INCENTIVES FOR USING
MODULAR UPS IN DATA CENTRES
As data centres
strive for higher
availability, they
deploy redundancy
at all infrastructure
levels, from entire
installations down
to devices within
them. Here, Alex
Emms, Operations Director at Kohler
Uninterruptible Power (KUP), introduces
this ubiquitous technique. He then explains
how modular UPS technology can contribute
to its success - while also improving power
e iciency, which is another key data centre
objective.
Availability at all levels
According to a recently-released Uptime
Institute report, ‘Annual Data Center Survey
Results 2019’, distributed resiliency using
active-active data centres is becoming more
common. 40 percent of those surveyed said
they use availability zones for resiliency - a
strategy that requires at least two active data
centres replicating data to each other.
Active-active strategies are also found at server
level, where they are implemented using server
clustering. To clients, the cluster behaves as a
single server with one IP address. While activepassive
configurations are possible, where one
server is online while others stand by, active-active
solutions, where each node shares the workload, are
increasingly preferred. These o er more computing
capacity as multiple servers are available for
processing, while also providing redundancy; if one
server fails, the others continue servicing the critical
load without interruption.
UPS installations have always supported improved
availability through redundancy, even before
modular designs. A 400kVA load, for example, could
be supported by a single 400kVA monolithic UPS
to provide capacity-only protection. Alternatively,
two such units could support the load with N+1
redundancy. However, the user had to purchase
double the UPS capacity they really needed, while
neither unit is ever more than 50 percent loaded –
and for transformer-based monolithic systems, this
severely impacts operating e iciency and increases
the cooling load.
The arrival of modular UPSs resolved these issues.
The above 400kVA load could be met with a KUP
PowerWAVE 9500DPA rack (Fig.1), populated with
four 100kVA modules - or five, for N+1 redundancy.
Only 20 percent, rather than 50 percent of the total
capacity is needed for the same redundancy.
Crucially, the PowerWAVE 9500DPA’s modules
can be hot-swapped, reducing repair times from an
monolithic’s average of 6 hours down to typically
30 minutes. Accordingly, modular systems can o er
‘six nines’ or 99.9999 percent availability, compared
with 99.9995 percent for legacy solutions.
Modularity improves e iciency too
Transformerless modular systems o er e iciency
improvements over their transformer-based
counterparts partly through their technology’s
inherently better e iciency, but also through
close matching to their critical load. Being
more fully-loaded allows optimal operating
e iciency. However, data centre loads can be
both unpredictable and dynamic, so a UPS could
become severely underloaded – and if load levels
drop below 25 percent, even modular system
e iciency starts falling o .
Xtra VFI technology prevents this by
automatically adjusting the number of active
modules to meet current load requirements. Excess
modules are switched to standby, but remain
primed to transfer to active mode if the load
increases. Fig.2 shows how the Xtra VFI operating
mode can enhance e iciency at low load levels
for a PowerWAVE 9500DPA modular UPS system,
with 10 UPS modules (100kW) and total available
capacity of 1MW.
Conclusion
We have seen how modular topology improves
both UPS availability and e iciency. However, to
achieve these results in practice, the underlying
hardware must be of robust design and
construction, and professionally and regularly
maintained. Accordingly, it’s essential to discuss
your power protection requirements with a
reputable, well-resourced and experienced supplier
such as Kohler Uninterruptible Power to avoid risk of
a UPS failure and its consequences for profitability,
business continuity and reputation.
kohler-ups.co.uk uksales.ups@kohler.com
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