Simple But Powerful Centrifugal Chillers
Centrifugal chillers are used for cooling large buildings in a
centralized air conditioning system. There are other types of
chillers using screw compressors and reciprocating compressors.
These are usually smaller in size. Today's topic is about
centrifugal chillers - the ultimate choice for any air
conditioning installations higher than 500 RT (refrigeration
tons)
Basically, centrifugal chillers use centrifugal fans to move the
refrigerant within the chiller circuit. As with any
refrigeration circuit, there must be a compressor, a condenser,
an expansion device, and the evaporator.
In the case of the centrifugal chiller, the fan is the
compressor. Rotating at very high speeds, it is capable of
pressurizing the refrigerant gas so as to increase its
temperature. Because the pressure is so dependent on the
efficiency of the impeller of the compressor, the impeller is
very carefully designed to match the system.
The clearances between the impeller and the housing at the mouth
ring (impeller suction) are made very small so as to reduce
leaks back to the discharge.
Usually inlet vanes that throttle the gas control the flow of
the gas, and thus the chiller load. The expansion of the liquid
to gas is usually made through a fixed orifice.
The lubrication of the shaft bearings must be done within the
chiller itself. Oil passages and shaft driven pumps (with motor
driven pumps at startup) is made for lubrication.
The oil will find their way to the condenser and has to be
extracted back to the lubrication system. Usually there will be
an eductor system to suck back the oil to the oil sump.
Centrifugal chillers are usually designed for low-pressure
refrigerant like R-123a.
These chillers sometimes surge when running, and they are very
sensitive to sudden changes in loads. Therefore modern
centrifugal chillers make use of electronic microprocessors to
control the various parameters and timing in order to run
smoothly.
Indeed, when everything is perfect, the centrifugal chiller is
capable of extremely smooth operation.
Folks, be cool!
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