Hanbell RC2-F Series, Manual

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35
V
Pd
Pd'
V
Pd<Pd'
P
Pd, Pd'
V
Pd=Pd'
P
Pd>Pd'
Pd'
Pd
P
3. Hanbell recommends monitoring oil pressure differential by pressure differential switch passively or by
additional oil pump actively and keep it 4
G cm kg
2
/
over the suction pressure for adequate seal, lubrication
and capacity control. This is very important especially when the condensing temperature is low and the
evaporating temperature is high like the application in water-cooled flooded chillers and normally its high-low
pressure differential tends to be less than 4
G cm kg
2
/
. In this kind of situation, installation of oil pump is
recommended to ensure sufficient oil supply.
4. All models
’ motor cooling are by refrigerant returned from evaporator. If compressors run continuously at
partial load below 50%, failure of motor coils might happen due to insufficient motor cooling. Therefore,
Hanbell emphasizes installation of liquid injection system to motor to make sure adequate cooling at motor
coils for safe running of compressors.
5. Contact with Hanbell to verify potential operating conditions outside the limits shown.
2.6 Compressor design feature
2.6.1 Compressor volume ratio
The Volume ratio (Vi) of the compressor can be defined as the ratio of suction volume of gas divided by discharge
volume of gas of the compressor. The volume ratio directly affects the internal compression ratio or Pi of the
compressor. A low Vi compressor corresponds to a low compression ratio compressor and high Vi compressors
are used on higher compression ratio systems. In the equation below, in order to avoid over or under compression,
the system compression ratio (CR) should be equal to the compressor internal compression ratio (Pi) . If CR is not
equal to Pi, it would cause extra compensation of work / power of compressor and also decrease C.O.P. Refer
also to the P-V (pressure
– volume) diagram below to show the relation.
CR =
Pd/Ps
Pi = Vi
k
Vi = Vs/Vd
Where: CR: system compression ratio Pi: internal compression ratio
Vi: internal volume ratio Pd: system pressure (absolute pressure)
Pd’:
discharge pressure (absolute pressure) Ps: suction pressure (absolute pressure)
Vs: suction volume Vd: discharge volume K: refrigerant specific heat ratio
Under compression (CR > Pi) Over compression (CR < Pi) CR = Pi
Loss of work
Loss of work
1
2
3
4
Ps
1
2
3
4
Ps
Ps
1
2
3
4
1