Johnson Controls YEWS Series, Installation, Operation And Maintanance Instructions

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2.1 INTRODUCTION
YORK YEWS series chillers (Heat pumps) are designed
for water cooling (heating) and to be located inside
building (Equipment room).
2.2 COMPRESSOR
A semi-hermetic screw compressor is provided to ensure
high operational efficiency and reliable performance.
Capacity control is achieved through slide valve. The
compressor is a positive displacement type characterized
by two helically grooved rotors, which are manufactured
from forged steel. The motor operator operates at 50Hz or
60Hz to directly drive the male rotor, which in turn drives
the female rotor on the light film of oil.
Each compressor is direct drive, semi-hermetic, rotary
twin screw type and includes the following items:
Two screw rotors, manufactured from forged steel.
A cast iron compressor housing precisely machined.
A built-in high efficient oil separator
An internal discharge check valve can prevent rotor
backspin during shutdown.
A suction vapor cooled, high efficient and reliable semi-
hermetic motor has overload protection: thermistor and
current overload protection.
A suction vapor screen and a serviceable oil filter are
installed in the compressor housing. For YEWS P serie
units, the oil filter is placed on the oil supply line.
Refrigerant vapor is sucked into the void created by the
unmeshing of the five lobed male and six lobed female
rotors. Further meshing of the rotors closes the rotor
threads to the suction port and progressively compresses
the vapor in an axial direction to the discharge port. The
vapor is compressed in volume and increased in pressure
before exiting at a designed volume at the discharge end
of the rotor casing. Since the intake and discharge cycles
overlap, a resulting smooth flow of vapor is maintained.
2 PRODUCT DESCRIPTION
The rotors are housed in a cast iron compressor housing
precision machined to minimize the void between the
housing and the rotors. Contact between the male and
female rotor is primarily rolling on a contact band on each
of the rotor's pitch circle. It result in virtually no rotor
wear and increased reliability.
The compressor incorporates a complete antifriction bear-
ing design for reduced power input and increased relia-
bility. Four separated, cylindrical, roller bearings handle
radial loads. Angular-contact ball bearings handle axial
loads. Together they maintain accurate rotor positioning at
all pressure ratios, thereby minimizing leakage and maint-
aining efficiency.
Motor cooling is provided by refrigerant vapor from the
evaporator flowing across the motor. Over load protection
includes overheat and current overload protections.
For YEWS H serie units, oil is removed from the
refrigerant using a built-in oil separator, and then returned
back to the compressor for lubrication. A plug-in heater
and a float ball type oil level swithch are located in the
compressor.
Motor Starting
Star/Delta (S/D) open transition starter is used for
compressor motor starting. The S/D starter utilizes 3
motor contactors and a starting relay. The starter allows
inrush current to be limited to approximately 33%LRA for
the first 4~10 seconds, with current changing to normal
running current when the Delta connection is established.
When the microprocessor initiates a start signal to run a
compressor, the applicable relays are energized. The tran-
sition of the relay contacts enables the 'Star' connection of
the motor start. The 'Star' connection of the motor start is
enabled for 4~10 seconds, then motor switchs to the
'Delta' connection.
Capacity Control
The compressors should start at the minimum load
YEWS-E Water Cooling Screw Chiller/Heat Pump