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CPD Programme
CPD Programme
The CIBSE Journal CPD Programme programme is free and can be used by any
Members of the Chartered Institution of reader. It is organised jointly by CIBSE Journal
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development (CPD) means the systematic in accordance with their institution’s guidance.
maintenance, improvement and broadening Simply study the module and complete the
of your knowledge and skills, and is therefore questionnaire on the final page, following the
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The quiet revolution in chillers
Developments in centrifugal compressors over the last five years have
produced packaged water chilling equipment with considerably higher
operating efficiencies than comparable compressors. The chillers are
marketed in the capacity range 300 to 1,500kW; and this CPD module
presents the new technology of the compressor and the chiller, together
with a recent case study to illustrate the application
B
y way of introduction, centrifugal volute, where some of the kinetic energy is the effectiveness of heat exchange;
compressors have been used in converted to pressure. The compressor may l Flooded evaporators that ensure optimum
refrigeration applications for contain one or more impellers, therefore energy transfer between refrigerant and
many years at the large-capacity single or multistage, depending on the water;
end of the market, beyond about 500kW pressure ratio required for the application. l Inverter-controlled compressors whose
cooling capacity. In the air conditioning Advantages of centrifugal compressors output can be precisely matched to the load;
field the refrigerant R134a is now generally over other types include the following: and
used, although in industrial applications l The impeller is the only moving part; l Use of a liquid refrigerant pump system
propane and ammonia are often selected. l Noise and vibration are low; that significantly increases thermodynamic
The centrifugal compressor is different l Lubrication is only required for the efficiency across the chiller’s operating
in operation to reciprocating, screw, scroll bearings; and range.
or vane compressors, which are positive l They are compact in size.
displacement machines and achieve the Recent features that have been introduced or Magnetic bearings
pressure rise by reducing the volume of the developed for centrifugal chillers, and which This is a digitally controlled system
gas. In a centrifugal compressor, suction gas result in energy savings, are: consisting of both permanent magnets
enters the eye of the spinning impeller and is l Magnetic bearings within the and electro magnets, which replace the
thrown by centrifugal force to the periphery compressor; conventional lubricated bearings. Figure 1
of the impellor. The blades of the impeller l Oil-free compressor; shows the main components of the system.
impart a high velocity to the gas and build l Floating head pressure; The compressor shaft rotates on a levitated
up the pressure. From the impeller the gas l Micro-channel aluminium condensers, that magnetic cushion and magnetic bearings
flows either into diffuser blades or into a reduce refrigerant charge while increasing (two radial and one axial) hold the shaft in >
www.cibsejournal.com July 2009 CIBSE Journal 49
CIBSEjul09 pp49-52 cpd.indd 49 25/6/09 16:08:54
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