Specifications

12
If the oil pressure falls below the values specified in Table 1
during start-up, the PIC III control will shut down the chiller.
Table 1 — Oil Pressure Requirements
Oil Reclaim System — The oil reclaim system recovers
oil from the cooler, removes the refrigerant, filters and returns
the oil back to the compressor. One or more oil reclaim nozzles
are positioned along the length of the cooler to draw the oil and
refrigerant mixture from the surface of the refrigerant level.
The mixture passes through an oil reclaim modulating valve
and into the vaporizer. The flow of refrigerant and oil is regu-
lated to prevent the vaporizer from becoming overloaded with
liquid refrigerant. The modulating valve position is adjusted in
accordance with the difference between the VAPORIZER
TEMP and the EVAP REFRIG LIQUID TEMP. The 4 to 20
mA signal from CCM terminals J8-3 and J8-4 is converted into
a 0 to 10V DC input to the oil reclaim modulating valve by a
500 ohm resistor connected between CCM terminals J8-3 and
J8-4. The oil reclaim modulating valve closes when the chiller
is shut down to prevent the vaporizer and oil sump from being
flooded with refrigerant. Do not manually open the oil reclaim
modulating valve when the chiller is shut down. Doing so will
severely degrade the viscosity of the oil in the sump. Flow of
refrigerant and oil from the cooler can be observed through a
sight glass on top of the vaporizer.
The viscosity of the compressor oil is significantly reduced
when it absorbs refrigerant. A combination of heat and low
pressure is used to vaporize the refrigerant that has been
absorbed by the oil mixture reclaimed from the cooler.
Condenser gas is used to warm the refrigerant and oil mixture
in the vaporizer. Warm refrigerant is bled from the top of the
condenser, directed through a row of tubes that line the bottom
of the vaporizer, and discharged into the cooler. A 1500 W
surface mounted electric heater provides supplemental heat to
the vaporizer when the compressor is operating at lower loads.
Refrigerant boiled out of the reclaimed mixture is vented to the
compressor suction. The concentrated oil mixture drains out of
the vaporizer, through a sightglass, past the vaporizer tempera-
ture sensor, and into the oil sump. A 530 W oil sump heater
maintains the temperature of the reclaimed oil and the oil
returned from the compressor at approximately 90 F (32.2 C)
when the chiller is running and 140 F (60 C) when the chiller is
off. The oil sump is also vented to compressor suction to
increase oil viscosity by boiling off additional refrigerant.
Capacity Control — The PIC III controls provide chilled
liquid temperature control by modulating the frequency of the
power delivered by the VFD to the compressor motor. The
compressor speed is adjusted in response to the difference be-
tween the CONTROL POINT and the LEAVING CHILLED
LIQUID or ENTERING CHILLED LIQUID temperatures.
The PIC III controls respond to the difference between the
CONTROL POINT and LEAVING CHILLED LIQUID
temperatures when the ECL CONTROL OPTION is
DISABLED.
The PIC III controls respond to the difference between the
CONTROL POINT and ENTERING CHILLED LIQUID
temperatures when the ECL CONTROL OPTION is
ENABLED.
The chiller capacity is controlled by varying the TARGET
VFD SPEED from 0% to 100%. The PIC III controls monitor
the compressor oil properties and set a COMPRESSOR MINI-
MUM SPEED to ensure sufficient compressor bearing lubrica-
tion under all operating conditions.
CONTROLS
Definitions
ANALOG SIGNAL — An analog signal varies in proportion
to the monitored source. It quantifies values between operating
limits. (Example: A temperature sensor is an analog device be-
cause its resistance changes in proportion to the temperature,
generating many values.)
DISCRETE SIGNAL — A discrete signal is a two-position
representation of the value of a monitored source. (Example: A
switch produces a discrete signal indicating whether a value is
above or below a set point or boundary by generating an on/off,
high/low, or open/closed signal.)
General Controls Overview — The 23XRV hermetic
screw liquid chiller contains a microprocessor-based control
center that monitors and controls all operations of the chiller.
The microprocessor control system matches the cooling
capacity of the chiller to the cooling load while providing
state-of-the-art chiller protection. The system controls cooling
capacity within the set point plus the deadband by sensing the
leaving chilled liquid or brine temperature (see Fig. 9 and 10)
and regulating the compressor speed. Reducing the compressor
speed decreases the volume flow rate of refrigerant through the
compressor. Chiller protection is provided by the PIC III
processor, which monitors the digital and analog inputs and
executes capacity overrides or safety shutdowns, if required.
TIME
(SEC)
MINIMUM START-UP OIL
PRESSURE REQUIREMENT
HFC-134a
PSID kPaD
Before Oil Pump On < 4 27.6
After Oil Press Verify Time 18 124
During Start/Run 15 103
SHRINK WRAP
STRAIN RELIEF
1/8” NPT
THERMOWELL
REMOVABLE
TEMPERATURE
SENSOR
Fig. 9 — Control Sensors (Temperature)
Fig. 10 — Control Sensors
(Pressure Transducers)
a23-1624
a19-957