GOING GREEN
35
Mitigating an UPS system’s
By Kohler Power
www.kohler-ups.co.uk
A data centre UPS is a significant, high-performance unit
that can both impact and be impacted by its environment in
various ways. So, we’re going to look at these environmental
factors, and how to mitigate them.
Temperature
All UPS have a maximum operating temperature, as quoted
by their manufacturers, of typically +40°C. The installation’s
air conditioning plant must have sufficient capacity to keep
the UPS’s environment below this limit. The UPS’s own
efficiency will significantly affect the air conditioning plant’s
size and operating costs. Additionally, the air conditioning
must be able to keep the ambient temperature at a level
suitable for any batteries installed alongside, which should
be 20°C
Humidity
UPS manufacturers state maximum permissible relative
humidity levels – of typically 95% – for their products. While
most UPS equipment is well designed, high relative humidity
levels may promote corrosion of cabinets and internal parts.
Simple dehumidification equipment is available for sites
where this may be a problem.
Audible noise
The unit of sound intensity is the decibel (dB) and it
represents the ratio between the sound level measured with
a microphone and a reference level, 0db, which is defined to
be approximately equal to the threshold of human hearing.
However, as the human ear is less sensitive to very low and
very high frequencies, an additional ‘A’ filter is applied when
measuring background or other intrusive noises, hence the
dBA unit used by all UPS manufacturers.
Typical audible noise figures for fully-loaded UPS
equipment range from 50dBA for 5kVA to 75dBA at 300kVA.
By comparison, rustling leaves create 20dBA sound levels,
environmental impact
and susceptibility
while a vacuum cleaner creates 50dBA. 120dBA is regarded
as the threshold of pain. The acceptable audio noise output
for any UPS depends on the application and installation
location. Check the manufacturer’s quoted level to ensure
the installation will create the minimum disturbance.
Energy use and efficiency
All organisations are motivated to improve energy
efficiency, not only because of fuel costs but also because
their stakeholders expect to see evidence of effective green
policies. These matter increasingly to employees, trading
partners and investors, while government policies penalise
poor energy efficiency performance.
An organisation’s UPS strategy will impact its energy
efficiency. In particular, this will suffer if legacy, transformer-
based UPS are still in use. Such UPS have a typical efficiency
of around 93% when fully loaded, dropping to about
90% at 50% loading, and even less at lower levels. This is
important because many sites have oversized their capacity
due to unrealistically high growth projections and are
running with a low loading as a result.
Efficiency can be greatly improved by upgrading to
a modern, modular installation that uses scalable UPS
modules. Such systems can be right-sized to avoid wasted
capacity and improve operating efficiency. In any case,
transformerless UPS’ efficiency is higher, and their
efficiency/loading curves are flatter than their transformer-
based equivalents. Accordingly, a modern, modular,
transformerless-design UPS has a typical efficiency of about
96% when fully loaded and this drops to about 95% for
loads between 25% and 75%. Additionally, transformerless
UPS produce an input power factor much closer to unity
and are less load-dependent than transformer-based types.
This will reduce the input current magnitude and associated
cabling and switchgear sizing, and, in some instances,
reduces electricity running costs. n
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