YZ Engineering Guide
Form: 161.01-EG1 (0618)
8
Equipment Overview
YORK® YZ Centrifugal Chillers are completely factory-packaged including the compressor, motor, VSD, OptiView
™
control center, evaporator, condenser, purge unit, and all interconnecting unit piping and wiring.
When selected, the initial charge of refrigerant can be supplied for each chiller from the factory. Actual shipping
procedures for the chiller will depend on a number of project-specific details. YZ chillers are designed to keep installation
costs low. Where installation access is not a problem, the unit can be shipped completely packaged including the unit-
mounted variable speed drive, requiring minimal piping and wiring to complete the installation.
At start-up, the services of a Johnson Controls factory-trained, field service representative are required to supervise or
perform the final leak testing, charging, initial start-up, and concurrent operator instructions.
COMPRESSOR
Note
: Please refer to the YZ Operations & Maintenance Manual (161.01-OM1) for a complete description of features and
functionality.
The compressor is a single-stage centrifugal design directly driven by a hermetically-sealed motor with a VSD. A cast-
aluminum, fully-shrouded impeller is mounted directly to the motor shaft. Impeller seals employ a labyrinth geometry,
sized to provide minimal thrust loading on the impeller throughout the operating range. The impeller is dynamically
balanced and overspeed tested for smooth, vibration-free operation.
CAPACITY CONTROL
Capacity control is achieved by the combined use of variable speed control and mechanical flow regulation to provide
fully modulating control from maximum to minimum load. For normal air conditioning applications, the chiller can adjust
capacity from 100% to 10% of design, without the use of hot gas bypass (HGBP). For each condition, the capacity control
devices will be automatically adjusted to maintain a constant leaving chilled liquid temperature at optimized efficiency,
based on information fed by sensors located throughout the chiller.
YZ chillers are equipped with sophisticated capacity control as standard. Our capacity control is a patented combination
of centrifugal chiller hardware and software that expands the chiller operating range and improves chiller performance.
The capacity control continuously monitors the characteristics of the compressor discharge gas and optimizes the diffuser
spacing to minimize gas-flow disruptions from the impeller.
MOTOR
The compressor motor is a hermetically-sealed, high-speed induction motor supported by active magnetic bearings. The
bearing design provides a completely lubrication-free operating system. The motor rotor and stator are cooled by a
pressure driven refrigerant loop to maintain acceptable operating temperatures.
The active magnetic bearings are equipped with balancing systems to ensure smooth and reliable operation. In the event
of a power failure, the magnetic bearings will remain in operation throughout the compressor coast-down using an
uninterruptable power supply. Mechanical bearings are included as backup to the magnetic bearings and are designed
for rare emergency touchdown situations where both the main power and uninterruptable power supply fail.