Oil Reclaim System; Capacity Control; Controls; Definitions - Carrier AquaEdge 23XRV Start-Up, Operation And Maintenance Instructions Manual

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 sur-
face of the refrigerant level. The mixture passes through an oil
reclaim modulating valve and into the vaporizer. The flow of re-
frigerant and oil is regulated to prevent the vaporizer from be-
coming overloaded with liquid refrigerant. The modulating
valve position is adjusted in accordance with the difference be-
tween the Vaporizer Temp and the Evap Sat Temp. The oil re-
claim modulating valve closes when chiller is shut down to pre-
vent 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.
Viscosity of compressor oil is significantly reduced when it ab-
sorbs refrigerant. A combination of heat and low pressure is used
to vaporize refrigerant that has been absorbed by the oil mixture
reclaimed from the cooler. Condenser gas is used to warm the re-
frigerant and oil mixture in the vaporizer. Warm refrigerant is bled
from the condenser top, directed through tubes that line the bottom
of the vaporizer, and discharged into the cooler. A 1500 W electric
heater provides supplemental heat to the vaporizer when the com-
pressor is operating at lower loads. Refrigerant boiled out of the
reclaimed mixture is vented to the compressor suction. The con-
centrated oil mixture drains out of the vaporizer, through a sight
glass, past the vaporizer temperature sensor, and into the oil sump.
The oil sump heaters maintain 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 PIC6 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 re-
sponse to the difference between the CONTROL POINT and the
LEAVING CHILL WATER TEMP or ENT CHILL WATER
TEMP temperatures.
The PIC6 controls respond to the difference between the CON-
TROL POINT and LEAVING CHILL WATER TEMP tempera-
tures when the EWT CONTROL OPTION is DISABLED.
The PIC6 controls respond to the difference between the CON-
TROL POINT and ENT CHILL WATER TEMP temperatures
when the EWT CONTROL OPTION is ENABLED.
The chiller capacity is controlled by varying the TGT. VFD
SPEED from 0% to 100%. The PIC6 controls monitor the com-
pressor oil properties and set a Compressor Minimum Speed to
ensure sufficient compressor bearing lubrication under all operat-
ing conditions. It will limit the circuit capacity to Circuit Capacity
Limit% in the General Configuration Table.

CONTROLS

Definitions

ANALOG SIGNAL
An analog signal varies in proportion to the monitored source. It
quantifies values between operating limits. (Example: A tempera-
ture sensor is an analog device because 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 bound-
ary by generating an on/off, high/low, or open/closed signal.)

General

The 23XRV hermetic screw liquid chiller contains a touch screen
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. 14
and 15) and regulating the compressor speed. Reducing the com-
pressor speed decreases the volume flow rate of refrigerant
through the compressor. Chiller protection is provided by the PIC6
processor, which monitors the digital and analog inputs and exe-
cutes capacity overrides or safety shutdowns, if required.
SHRINK WRAP
STRAIN RELIEF
REMOVABLE
TEMPERATURE
SENSOR
Fig. 14 — Control Sensors (Temperature)
Fig. 15 — Control Sensors (Pressure Transducers)

PIC6 System Components

The chiller control system is called PIC6. See Fig. 16-21 and Ta-
ble 2. The PIC6 system controls the chiller by monitoring all oper-
ating conditions. The PIC6 control system can diagnose a problem
and let the operator know what the problem is and what to check.
It promptly adjusts compressor speed to maintain leaving chilled
liquid temperature. It can interface with auxiliary equipment such
as pumps and cooling tower fans to turn them on when required. It
continually checks all safeties to prevent any unsafe operating
condition. It also regulates the oil heater and regulates the hot gas
bypass valve, if installed. The PIC6 control system provides criti-
cal protection for the compressor motor and control of the variable
frequency drive.
The PIC6 control system supports native CCN and LEN protocols
and can communicate via CCN to other PIC I, PIC II, PIC III, and
PIC6 equipped chillers or other CCN devices. PIC6 has native ca-
pability to communicate with building automation system via
BACnet MS/TP, BACnet/IP, Modbus
1
TCP/IP. The PIC6 controls are housed inside the control center en-
closure. See Fig. 2-4. The component names are listed in Table 2.
1. BACnet is a trademark of ASHRAE.
2. Modbus is a registered trademark of Schneider Electric.
17
1/8" NPT
THERMOWELL
RTU, and Modbus
2