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 pin screw manufacturers 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.

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