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TRG-TRC010-EN 13
period one
Components
notes
chiller’s refrigeration system—and uses a coupling to connect the motor and
compressor shafts.
The heat generated by the hermetic motor is absorbed by liquid refrigerant that
flows around, through, and over the motor. The heat must be rejected by the
chiller’s condenser.
The heat generated by the open motor is rejected to the air drawn in from the
equipment room. This heat must still be rejected from the equipment room,
either by mechanical ventilation or, if the room is conditioned, the building’s
cooling system. In some designs, this air is simply drawn into the motor
housing by the rotating motor shaft. The vent passages tend to get dirty and
clog, resulting in higher operating temperatures and hot spots that adversely
affect motor efficiency and reliability. Other designs, such as totally-enclosed
fan-cooled (TEFC) and totally-enclosed air-over (TEAO), use a separate fan with
a protective housing to cool the motor.
Hermetic compressor motors eliminate the need for the shaft couplings and
external shaft seals that are associated with open motors. The coupling needs
precise alignment, and these seals are a prime source of oil and refrigerant
leaks. On the other hand, if a motor burns out, a hermetic chiller will require
thorough cleaning, while a chiller with an open motor will not.
Controls and Starter
A microprocessor-based control panel is provided on the chiller to provide
accurate chilled-water control as well as monitoring, protection, and adaptive
limit functions. These controls monitor chiller operation and prevent the chiller
from operating outside its limits. They can compensate for unusual operating
conditions, keeping the chiller running by modulating system components
rather than simply shutting it down when a safety setting is violated. When
serious problems occur, diagnostic messages aid troubleshooting.
Modern control systems not only provide accurate, optimized control and
protection for the chiller, but can also interface with a building automation
system for integrated system control. In a chilled water system, optimal
Controls and Starter
control
control
panel
panel
starter
starter
Figure 20
trgtrc010_book.book Page 13 Wednesday, September 1, 1999 10:39 AM