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28 TRG-TRC010-EN
notes
period three
Compressor Capacity Control
The starting point (A) is the full-load operating point. As the load on the chiller
decreases, the inlet vanes partially close, reducing the flow rate of refrigerant
vapor through the compressor and balancing the chiller capacity with the new
load (B).
Less refrigerant, and therefore less heat, is transferred to the condenser. Since
the heat rejection capacity of the condenser is now greater than required, the
refrigerant condenses at a lower temperature and pressure. This reduces the
pressure difference between the evaporator and the condenser.
Continuing along the unloading line, the compressor remains within its stable
operating range until it reaches the surge region at C.
compressor map for a
2-Stage Compressor
25
25
75
75
10
10
14
14
63
63
pressure difference
pressure difference
refrigerant flow rate
refrigerant flow rate
s
u
r
g
e
s
u
r
g
e
90
90
36
36
51
51
&
%
$
unloading line
unloading line
Figure 41
trgtrc010_book.book Page 28 Wednesday, September 1, 1999 10:39 AM