Johnson Controls YORK YVAM 0350, Operation & Maintenance Manual

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Motor
The compressor motor is a hermetic permanent magnet high-speed design with magnetic
bearings. The compressor impeller is overhung from the end of the motor shaft and has no
bearings of its own.
The motor includes angular contact ball bearings only engaged with the rotor shaft during
shutdown after rotation is stopped or during shutdown due to loss of power to the magnetic
bearings.
The bearing control center maintains correct shaft position in the magnetic bearings.
Heat exchangers
The evaporator shell is fabricated from rolled carbon steel plates with fusion welded seams. Heat
exchanger tubes are internally enhanced type.
Evaporator
The evaporator is a shell and tube, hybrid falling film, and flooded type heat exchanger. A
distributor trough provides uniform distribution of refrigerant over tubes in the falling film section.
Residual refrigerant floods the tubes in the lower section. Suction baffles are located above the
tube bundle to prevent liquid refrigerant carryover into the compressor. A 2 in. liquid level sight
glass is located on the side of the shell. The evaporator shell contains dual refrigerant relief valves.
Condenser
The 10 condenser sections are microchannel design and consist of a tube and fin design. Each
condenser section has two cooling fans that are speed controlled from the chiller control panel
and use VSD technology to operate the fans. Refrigerant sub-cooling is accomplished in the
condenser section. Refrigerant relief valves are located on the system discharge piping that feeds
the condenser sections with refrigerant isolation valves as standard options.
Waterboxes
The removable compact waterboxes are fabricated of steel. The design working pressure is 150
psig (1,034 kPa) and the boxes are tested at 225 psig (1,551 kPa). Integral steel water baffles
provide the required pass arrangements. Stub-out water nozzle connections with grooved
connections, which are a standard option, are welded to the waterboxes. These nozzle connections
are suitable for groove type couplings, welding, or flanges, and are capped for shipment. Plugged
3/4 in. drain and vent connections are provided in each waterbox.
Refrigerant flow control
Refrigerant flow to the evaporator is controlled by the condenser drain valve. The control panel
monitors the condenser subcooling value as the control point for the condenser drain valve.
Under program control, the control panel modulates the condenser drain valve to control the
condenser refrigerant level to the programmed subcooling setpoint. Other setpoints modify the
control sensitivity and response. Only a qualified service technician can change these settings. The
subcooling setpoint must be verified at chiller commissioning by a qualified service technician.
While the chiller is shut down, the condenser drain valve is pre-positioned to anticipate run. When
the chiller is started, if the subcooling value is less than the setpoint, a linearly increasing ramp is
applied to the subcooling setpoint. This ramp causes the setpoint to go from the initial subcooling
value to the programmed setpoint over a programmable period of time. If the actual subcooling
value is greater than the setpoint upon run, it immediately begins to control to the programmed
setpoint.
While the chiller is running, the refrigerant level is normally controlled to the subcooling setpoint.
13 YVAM Control Center