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CPD Programme
when the compressor cycles off, they have the
ability to reverse and blow out dust that has
gathered on the coil surfaces. This feature
helps to maintain coil efficiency and overall
energy consumption.
Figure 3 shows a water cooled centrifugal
chiller incorporating the new compressor,
available for applications using cooling towers
or dry coolers.
Liquid pressure amplification system
Figure 4 shows the principle of a liquid
pressure amplification system, which can
circulate liquid refrigerant from the condenser
to the evaporator at low ambient temperatures,
without running the compressor. For example,
if the ambient is 10 deg C db, the air cooled
condenser may cool refrigerant to 12/14 deg
C, which could meet the cooling requirement.
This has been incorporated into the new
centrifugal chillers, where a 1kW liquid pump
increases cooling capacity at all condensing
temperatures, but has greatest effect at lower
temperatures. This glycol-free alternative to
conventional free-cooling is highly efficient, Figure 3 Water cooled centrifugal chiller
and dramatically reduces energy consumption
while maintaining refrigeration performance.
WINTER SUMMER
A secondary benefit of the reduced compressor
run-time is extended plant life. With the
Condenser+fan Condenser+fan
low-power liquid pump taking the load, the
+ +
– –
compressor does not have to work so hard or
LPA pump S.V. on LPA pump S.V. off
E.E.V. off E.E.V. on
for so long, reducing wear and the likelihood
of breakdown. S.V. off S.V. on
– –
Case study
E
vaporator
+
E
vaporator
+
A recent project has been the replacement of
chillers and cooling towers at the Dorchester
Hotel in London. The original R22 chillers
were in the basement with a condensing water
Compressor off Compressor on
riser to the cooling towers on the roof. They Figure 4 Liquid pressure amplification system
were removed in stages as they were replaced
by three of the new centrifugal chillers on the towers, and the condensing water riser was of its innovative design, the machine requires
roof, each with a cooling capacity of 1MW and converted to carry chilled water. The third 30 per cent less refrigerant than comparable
each containing three compressors. Even chiller was placed on the roof of the third conventional chillers, reducing servicing costs
though cooling towers generally deliver more rear floor, freeing up the basement plant and potential environmental damage from
efficient operation than air-cooled condensers, room. There were strict planning conditions large-scale leakage.
such is the efficiency of the new chillers that regarding noise, and it is intriguing that the
© Terry Welch
energy costs have been reduced by £10,000 a new chillers are quieter than the previous
Steve Chaplin (Klima-Therm)
month compared with the previous system. cooling towers.
These savings are expected to achieve a It is claimed that this new breed of centrifugal References
payback in the first year on the additional chillers is “probably the most efficient HFC- Engineerlive, www.engineerlive.com/Energy-
capital cost, compared with a conventional based chiller in the world”, able to achieve Solutions/Heat_Recovery
screw chiller. There are also savings in water energy efficiency ratios of 10 and above. The ACR News, August 2008, www.acr-news.com
treatment and chemical costs associated technology can reduce end users’ power bills by DatacentreManagement, 26 January 2009,
with the cooling towers. The analysis of the between 30 and 50 per cent, while at the same Chillers come of age
cooling load throughout the year suggests a time dramatically cutting carbon emissions. On Modern Building Services, “Geoclima
£90,000-a-year saving compared with a screw some applications, the saving can cut pay-back develops new chiller range based on Turbocor
compressor chiller – a 30 per cent saving. Two time to less than a year. The performance claims compressor”, June 2009
chillers were positioned on the roof of the 10th have been independently verified by a leading HPAC Engineering, January 2004, “Frictionless
floor in space previously occupied by cooling consultant at a test facility in Italy. As a result Compressor Technology”
www.cibsejournal.com July 2009 CIBSE Journal 51
CIBSEjul09 pp49-52 cpd.indd 51 26/6/09 12:15:56
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