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Operating Principles
General Requirements
Operation and maintenance information for CDHF and
CDHG CenTraVac™ chillers are covered in this section.
This includes both 50 and 60 Hz centrifugal chillers
equipped with the Tracer® AdaptiView™ UC800
control system. This information pertains to all chiller
types unless differences exist, in which case the
sections are listed by chiller type as applicable and
described separately. By carefully reviewing this
information and following the instructions given, the
owner or operator can successfully operate and
maintain a CenTraVac™ chiller. If mechanical problems
do occur, however, contact a Trane service technician
to ensure proper diagnosis and repair of the unit.
I I m m p p o o r r t t a a n n t t : : Although CenTraVac™ chillers can operate
through surge, it is NOT recommended to
operate them through repeated surges over
long durations. If repeated surges of long
durations occur, contact your Trane Service
Agency to resolve the issue.
Cooling Cycle
Duplex™ CenTraVac™ chillers have two refrigerant
circuits that operate as their own independent circuits.
These circuits are discussed as individual chiller
refrigeration units in the following section. The
sequence of operation of the two refrigeration circuits
is discussed in a later section.
When in the cooling mode, liquid refrigerant is
distributed along the length of the evaporator and
sprayed through small holes in a distributor (i.e.,
running the entire length of the shell) to uniformly coat
each evaporator tube. Here, the liquid refrigerant
absorbs enough heat from the system water circulating
through the evaporator tubes to vaporize. The gaseous
refrigerant is then drawn through the eliminators
(which remove droplets of liquid refrigerant from the
gas) and the first-stage variable inlet guide vanes, and
into the first-stage impeller.
CDHG 3-Stage Compressor 1 or 2
Compressed gas from the first-stage impeller flows
through the fixed, second-stage inlet vanes and into
the second-stage impeller. Here, the refrigerant gas is
again compressed, and then discharged through the
third-stage variable guide vanes and into the third-
stage impeller. After the gas is compressed a third
time, it is discharged into the condenser. Baffles within
the condenser shell distribute the compressed
refrigerant gas evenly across the condenser tube
bundle. Cooling tower water circulated through the
condenser tubes absorbs heat from the refrigerant,
causing it to condense. The liquid refrigerant then
passes through an orifice plate and into the
economizer.
CDHF-SVX01N-EN
The economizer reduces the energy requirements of
the refrigerant cycle by eliminating the need to pass all
gaseous refrigerant through three stages of
compression (refer to the following figure). Notice that
some of the liquid refrigerant flashes to a gas because
of the pressure drop created by the orifice plates, thus
further cooling the liquid refrigerant. This flash gas is
then drawn directly from the first and second stages of
the economizer into the third- and second-stage
impellers of the compressor, respectively. All
remaining liquid refrigerant flows through another
orifice plate to the evaporator.
Figure 46. Pressure enthalpy curve, 3-stage
P
6
4
High Side Economizer
P
7
3
Low Side Economizer
P
8
2
Evaporator
P
1
1
Enthalpy
Figure 47. Refrigerant flow, 3-stage
CDHF 2-Stage Compressor 1 or 2
Compressed gas from the first-stage impeller is
discharged through the second-stage variable guide
vanes and into the second-stage impeller. Here, the
refrigerant gas is again compressed, and then
discharged into the condenser. Baffles within the
condenser shell distribute the compressed refrigerant
gas evenly across the condenser tube bundle. Cooling
tower water circulated through the condenser tubes
absorbs heat from the refrigerant, causing it to
Condenser
5
Compressor
Third Stage
4
Compressor
Second Stage
3
Compressor
First Stage
2
67
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