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Operating Principles
General Requirements
Operation and maintenance information for HDWA
Agility™ chillers are covered in this section. By
carefully reviewing this information and following the
instructions given, the owner or operator can
successfully operate and maintain a Agility™ 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 Agility ™ 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.
•
Agility ™ are selected, designed, and
built for a particular set of design
conditions. Operation outside of design
conditions may result in improper
operation. Refer to chiller selection for
minimum unloading.
Cooling Cycle
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 suction
connection and the first-stage variable inlet guide
vanes, and into the first-stage impeller.
HDWA Compressor
The unit is equipped with a semi-hermetic, direct-drive,
two-stage, centrifugal compressor that includes inlet
guide vanes for capacity control. The Adaptive
Frequency™ Drive (AFD) provides capacity control with
lower speeds. Compressed gas from the first-stage
impeller is discharged through the interstage pipe to
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 condense. The subcooled
liquid refrigerant then flows out of the bottom of the
condenser.
The liquid refrigerant is then split such that the primary
flow is directed through one side of the brazed plate
HDWA-SVX001D-EN
heat exchanger economizer, while a significantly
smaller portion of the flow passes through an
expansion valve, lowering refrigerant pressure and
temperature before entering the secondary side of the
BPHE as two-phase refrigerant. The heat transfer
between the primary and secondary channels in the
BPHE results in further subcooling of the primary liquid
as it rejects heat to, and consequently superheats, the
secondary flow. The additional subcooling of the liquid
prior to expansion through the main electronically-
controlled valve effectively increases the overall
capacity of the evaporator. In addition, the superheated
vapor bypasses the evaporator and first stage of
compression (the secondary BPHE flow is added prior
to the second stage of compression).
Figure 32. Refrigerant flow
Primary
4
Condenser
5
8
Secondary
6
Evaporator
9
Enthalpy
Compressor Motor
Two magnetic bearing modules levitate and align the
rotating assembly. The motor is permanent magnet
type and is cooled by refrigerant gas sourced from the
interstage pipe, metered through an orifice or
electronic expansion valve, and routed through the
bearing modules and motor windings.
Adaptive Frequency Drive
An Adaptive Frequency™ Drive (AFD) and control
panel is provided on every chiller. Microprocessor-
based unit control modules (Tracer® UC800) provide
for accurate chilled water control as well as monitoring,
protection, and adaptive limit functions. The "adaptive"
nature of the controls intelligently prevents the chiller
from operating outside of its limits, or compensates for
unusual operating conditions, while keeping the chiller
running rather than simply tripping due to a safety
concern. When problems do occur, diagnostic
messages assist the operator in troubleshooting.
3
Compressor
Second Stage
7
2
Compressor
First Stage
1
47
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