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38% energy reduction in data
centre cooling

Following a successful pilot project Excalibur Energy have completed the modification of six
chillers at two data centres.

Data centres offer a unique challenge to energy management; a constant
year round heat load means that cooling represents a significant energy
cost. The critical nature of the building means that a very conservative
approach to design and modification is adopted.
Excalibur Energy has been providing energy efficient solutions for heating
and cooling since 1980. When approached to investigate the potential
to reduce the energy consumption of chillers at two data centre, their
study showed that there was potential to reduce electrical consumption
by nearly 40%.
Excalibur proposed the installation of Liquid Pressure Amplification (LPA)
along with the chiller manufacturer’s recommendation of replacing the
existing condenser fans with more efficient EC fans.
Data centre technical staff had to be persuaded that modification of their
chillers would not affect the resilience of their building. A presentation
demonstrated the robust design and that no single point of failure would
be introduced as a result of the modifications.
Further confidence was gained by undertaking condition monitoring of
each refrigeration circuit using the Climacheck analyser to ensure the
chillers were in good working order prior to any works commencing.
Improved refrigeration efficiency is achieved by reducing compressor
discharge pressure; this is commonly referred to as “floating head
pressure”. Reducing discharge pressure affects efficiency in two ways;
absorbed power is reduced while cooling capacity is increased.
LPA allows the minimum discharge pressure to be reduced well below
what would normally be achievable, with improvements in efficiency of
25-35%.
If these operating parameters were maintained without the installation of
LPA, a condition commonly referred to as “over condensing” would be
experienced. This is where discharge pressure has been reduced to a level
that liquid refrigerant starts to evaporate before it reaches the expansion
valve, reducing capacity, efficiency and ultimately reliability.
LPA is located in the drain from the condenser and pumps liquid
refrigerant to the expansion valve maintaining a flow of good quality liquid
refrigerant at the expansion valve during low head pressure operation to
overcome this problem.
Generally head pressure control is achieved by cycling condenser fans on
and off, this is not accurate enough for floating head pressure operation.
Inverter or EC fan control allows all condenser fans to be operated
38% energy reduction in data
centre cooling
Following a successful pilot project Excalibur Energy have completed the modification of six
chillers at two data centres.
_case study
Energy Efficient Management
and their speed modulated to provide precise control of pressure. The
correct control allows discharge pressure to be continually optimised
against ambient temperature and cooling demand.
Installation of LPA requires the recovery of refrigerant and the fabrication
of a manifold on the discharge side of the condenser. Bypass pipework
ensures that in the event of a pump fault (generally as a result of a loss of
refrigerant) the chiller will continue to operate. The fault signal generated
will initiate an increase in head pressure to ensure that over condensing
does not occur.
The low refrigerant fault is generated when 5-10% of refrigerant has been
lost, and so provides an early warning that the chiller should be leak
tested.
Two 700kw, 2 – circuit chillers operating on R407c
were selected for the pilot. These chillers incorporate
free cooling coils, which would also show an increase
in capacity as a result of increased condenser fan
operation.
The energy consumption and cooling capacity of
both chillers was monitored for a period prior to
installation works being undertaken to provide a
baseline for efficiency.
Following the installation of LPA and EC condenser
fans the chillers were commissioned for floating head
pressure operation and the monitoring repeated.
The results over the period of monitoring showed
a reduction in absorbed power of 38% (see graph),
this represents an annual reduction in electrical
consumption of 325,000 kwh and 177 tonnes of CO²
for a single chiller.
The monitoring also demonstrated the effect that
the increased airflow generated by the more efficient
EC fans was having. Prior to modification the chillers
were able to entirely satisfy demand in free cooling
mode when external air temperatures fell below 1ºC.
Following the modifications, cooling demand could
be satisfied when air temperatures fell below 4ºC, a
further reduction in chiller energy consumption.

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