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desired liquid level in the cooler (as is done for Non-
Economized chillers). The float valve maintains a liquid level
in the bottom of the economizer. Liquid refrigerant is supplied
from the condenser to the bottom of the economizer. As the
refrigerant passes through the EXV, its pressure is reduced to
an intermediate level of about 500 kPa. This pressure is
maintained inside the economizer shell. Next, the refrigerant
flows through the float valve, its pressure is further reduced to
slightly above the pressure in the cooler. The increase in
performance is realized when some of the refrigerant passing
through the EXV flashes to vapor, further subcooling the liquid
that is maintained at the bottom of the economizer. This
increase in subcooling provides additional capacity. Since no
additional power is required to accomplish this, the efficiency
of the machine also improves. The vapor that flashes will rise
to the economizer where it passes to the compressor and is
used as needed to provide motor cooling. After passing over
the motor windings, the refrigerant reenters the cycle at an
intermediate port in the compression cycle.
14.7 - Oil pumps
The 30GX/HXC screw chillers use one externally mounted
pre-lubricating oil pump per circuit. This pump is operated as
part ot the start-up sequence.
ATTENTION: The operating temperature of the coil may
reach 80°C. In certain temporary conditions (especially
during start-up at low outside temperature or low condenser
loop temperature) the oil pump can be reactivated.
On 30GX units, the pumps are mounted to the base rails on the
oil separator side of the unit. The pumps are mounted to a
bracket on the condensers of 30HXC units. When a circuit is
required to start, the controls will energize the oil pump first so
that the compressor starts with correct lubrication. If the pump
has built up sufficient oil pressure, the compressor will be
allowed to start. Once the compressor has started, the oil pump
will be turned off. If the pump was not able to build up enough
oil pressure, the control will generate an alarm.
14.8 - Motor cooling valves
Compressor motor winding temperatures are controlled to the
optimum setpoint. The control accomplishes this by cycling the
motor cooling solenoid valve to allow liquid refrigerant to flow
across the motor windings as needed. On units equipped with
economizers, flash gas leaves the top of the economizer and
continually flows to the motor windings. All refrigerant used
for motor cooling re-enters the rotors through a port located
midway along the compression cycle and is compressed to
discharge pressure.
14.9 - Sensors
The units use thermistors (including two motor temperature
thermistors) and two level thermistors and pressure transducers
to monitor and control system operation.
14.10 - Thermistors
14.10.1 - Evaporator leaving fluid
This temperature is used to measure the leaving evaporator
fluid temperature (water or brine). The temperature is used for
leaving fluid temperature control and to protect against cooler
freeze-up. It is located in the evaporator fluid nozzle.
14.10.2 - Evaporator entering fluid
This sensor is used to measure the evaporator entering fluid
temperature. It is located in the entering evaporator nozzle. It is
used to provide automatic temperature compensation for the
leaving fluid temperature control with entering fluid compen-
sation.
14.10.3 - Discharge gas temperature (circuits A & B)
This sensor used to measure the discharge gas temperature and
control the discharge temperature superheat. It is located on the
discharge pipe of each circuit (30HXC) or on the top of the oil
separator (30GX).
ATTENTION: There is no thermostat sleeve.
14.10.4 - Motor temperature
The Compressor Protection Module (CPM) monitors the motor
temperature. Thermistor terminals are located in the
compressor junction box.
14.10.5 - Evaporator liquid level (circuits A & B)
Evaporator liquid level thermistor is used to provide optimized
flow control in the evaporator. It is installed in the top of the
evaporator.
14.10.6 - Condenser entering fluid (30HXC)
This sensor is used to measure the temperature of the fluid
entering the water cooled condensers. It is located in the
common fluid line entering the condensers (field installed). On
Heat Machines it is used by the capacity control routine. On
water cooled condensers it is only used for monitoring of the
condenser fluid temperature.
14.10.7 - Condenser leaving fluid (optional on 30HXC)
This sensor is used to measure the temperature of the fluid
leaving the water cooled condensers. It is located in the
common fluid line leaving the condensers (field installed). On
Heat Machines it is used by the capacity control routine. On
water cooled condensers it is only used for monitoring of the
condenser fluid temperature.
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