Operating Principles
74 CVHH-SVX001A-EN
more than four times in four hours, a latching diagnostic—
Purge Liquid Level Too High Continuously—will be
generated. The purge system will not restart until it is
reset.
If a Purge Liquid Level Too High Continuously diagnostic
occurs, check the purge lines for any type of restriction
(trapped liquid, closed valves, etc.) and ensure that the
filter-drier on the liquid return line is in good condition.
A UL-required pressure-relief device (fusible plug), which
protects against over-pressurization of the purge tank, is
mounted on the purge tank. The plug material will fuse at
98.9°C (210°F), which equates to approximately 910.1 kPag
(132 psig) for refrigerant R-1233
zd
(E).
Pump-out Subsystem
When the purge control subsystem detects the presence
of non-condensables in the purge tank, the pump-out
solenoid and exhaust solenoid valves open, and the
pump-out compressor turns on. The valves and the
compressor cycle on and off as needed to achieve an
efficient and fast removal of non-condensables.
A High Vacuum Pump option is available for applications
that require purge operation at low condensing
temperatures and pressures. This option provides a two-
stage pump-out compressor. The High Vacuum Pump
option allows the purge system to operate to saturation
temperatures as low as 1.1°C (34°F). Typical applications
that may require the High Vacuum Pump option include
free-cooling installations, series chiller installations, ice
systems having brine flowing through idle chillers, chillers
installed outdoors or in unconditioned spaces, or any
application that may cause very low condenser water
temperatures.
Carbon Tank and Regeneration Subsystem
The discharge from the pump-out compressor is piped
through the carbon tank. The special carbon in the tank
effectively scrubs and collects refrigerant molecules from
the non-condensable gas before the gas passes through
the exhaust solenoid valve to the chiller vent line.
A 175 W resistive heater is mounted inside the carbon tank
and is used to periodically “ regenerate” the carbon bed
and drive any collected refrigerant vapor back into the
chiller. A UL-required pressure-relief valve, rated at
1034.2 kPa (150 psi), is mounted on the line leaving the
carbon tank. The valve protects against over-
pressurization of the carbon tank.
A temperature sensor is installed through the top of the
carbon tank shell so that the controls can monitor the
carbon bed temperature. The temperature sensor controls
the regeneration cycle and protect against overheating. If
the limit temperature is reached, the system shuts down
and a Purge Carbon Regen Temperature Limit Exceeded
diagnostic is generated.
Sensors
The following sensors are used to enable control
communication between the Tracer UC800 controller and
the EarthWise purge system. The sensors use low-level
intelligence devices (LLIDs) to communicate with the
Tracer UC800 controller.
Compressor suction temperature sensor. This
sensor is mounted on the purge condensing unit suction
line. The controller uses the value of this temperature
sensor to decide whether or not to purge non-
condensables from the purge tank. When the temperature
drops to a specified point, the controller activates the
pump-out cycle to remove the accumulated non-
condensables from the purge tank. When enough non-
condensables have been removed and the purge
compressor suction temperature increases in response,
the controller terminates the pump-out cycle.
Saturated condenser temperature sensor. This
sensor is mounted on the chiller. If the chiller is running,
the controller uses the value of this temperature sensor to
adjust the purge pump-out initiate/terminate setpoints. It
may be used to prohibit pump-out, if system conditions
are too cool.
Saturated evaporator temperature sensor. This
sensor is mounted on the chiller. If the chiller is Off, the
controller uses the value of this temperature sensor to
adjust the purge pump-out initiate/terminate setpoints. It
may be used to prohibit pump-out, if system conditions
are too cool.
Carbon tank temperature sensor. This sensor is
mounted in the carbon tank of the purge system. It
provides feedback to the carbon regeneration algorithm.
The sensor and the controller function much the same as
a thermostat to control the carbon tank heater.
Liquid level sensor. This sensor resides in the purge
control panel. It monitors the status of the normally closed
float switch, which is mounted in the bottom of the purge
tank. If an adequate amount of liquid fails to drain from the
purge tank, the float switch and sensor detect the
condition and prevent further purge operation.
Condensing unit LLID. This LLID resides in the purge
control panel. It uses a high-capacity relay to control the
operation of the purge condensing unit.
Quad relay LLID. This LLID resides in the purge control
panel. It has four relay outputs that are used to control the
pump-out compressor, the carbon tank heater, the
regeneration solenoid valve, and an alarm output.
Dual triac LLID. This LLID resides in the purge control
panel. It has two triac-type outputs that are used to control
the pump-out solenoid valve and the exhaust solenoid
valve. The purge system draws its control power from the
power supplies of the chiller control panel.
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