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18 TRG-TRC010-EN
notes
period two
Refrigeration Cycle
The change in enthalpy from C to A that occurs during the refrigeration cycle is
called the refrigeration effect. This is the amount of heat that each pound
[kg] of liquid refrigerant will absorb when it evaporates.
The benefit of the economizer can be demonstrated by comparing the
refrigeration cycles with and without an economizer.
Without an economizer, refrigerant from the condenser ➅ expands directly to
evaporator conditions ➉, producing a smaller refrigeration effect (B to A).
Some chiller designs may subcool the liquid refrigerant in the condenser (➅
moves to the left) to increase this refrigeration effect.
Also, in a chiller without an economizer, all of the refrigerant vapor must go
through both stages of compression to return to condensing conditions. In a
chiller with an economizer, refrigerant vapor that flashes in the economizer
bypasses the first stage of compression, resulting in an overall energy savings
of 3 to 4 percent.
2-stage centrifugal chiller
Refrigeration Cycle
1
1
2
2
pressure
pressure
enthalpy
enthalpy
evaporator
evaporator
condenser
condenser
P
P
e
e
P
P
c
c
P
P
1
1
&%
$
6
6
7
7
9
9
5
5
2-stage
2-stage
compressor
compressor
economizer
economizer
3
3
4
4
expansion
expansion
devices
devices
10
10
8
8
Figure 26
trgtrc010_book.book Page 18 Wednesday, September 1, 1999 10:39 AM