Cycle - Trane PRGD series Installation, Operation And Maintenance Manual

the purge refrigerant exiting the coil. The compressor
suction temperature sensor monitors this temperature.
When sufficient non-condensables have accumulated
in the purge tank to decrease the compressor suction
temperature below the pump-out initiate value, a
pump-out cycle begins. The cycle is terminated when
the compressor suction temperature sensor increases
above the pump-out terminate value. The calculations
for the pump-out values are:
Pump-out initiate:
• (°F) = Purge liquid temperature (°F) – 50°F or 0°F
(whichever is higher)
• (°C) = Purge liquid temperature (°C) – 10.0°C or
-17.8°C (whichever is higher)
Pump-out terminate:
• (°F) = Purge liquid temperature (°F) – 40°F or 5°F
(whichever is higher)
• (°C) = Purge liquid temperature (°C) – 4.4°C or -
15.0°C (whichever is higher)
For factory installed purges or those retrofit purges that
communicate with the chiller control system, the purge
liquid temperature value comes from the chiller's
saturated condenser temperature sensor when the
chiller is running, or the chiller's saturated evaporator
temperature sensor when the chiller is off.
For a field installed retrofit purge that does not
communicate with the chiller control system, a purge
liquid temperature sensor is mounted on the purge
liquid drain line and the resulting temperature from
this sensor is used in the above equations.
Non-condensable Pump-out cycle
A non-condensable pump-out cycle may be initiated as
described below only if the following two conditions
are met:
PRGD-SVX01F-EN
S S e e q q u u e e n n c c e e o o f f O O p p e e r r a a t t i i o o n n s s
• a carbon regeneration cycle is NOT in process, and
• the refrigeration circuit is on.
If at any time, except as described above, the purge
refrigerant compressor suction temperature drops
below the pump-out initiate value, the following
sequence is initiated by the controls.
The controller starts the pump-out compressor and
opens the exhaust solenoid valve. After 5 seconds, the
pump-out solenoid valve opens and pulses at a rate of
20 seconds On and 20 seconds Off. If after two cycles,
the purge refrigerant compressor suction temperature
has not exceeded the pump-out terminate value, the
pump-out solenoid valve stays continuously open. If
the pump-out compressor runs for more than
10 consecutive minutes, the controller recalculates the
pump-out initiate and pump-out terminate values as
described.
The purge controls continue to operate the pump-out
solenoid valve and calculate values as described above
until the purge refrigerant compressor suction
temperature rises above the pump-out terminate value.
At this point, the controller will close the pump-out
solenoid valve and turn off the pump-out compressor
and exhaust solenoid valve.
Typical pump-out cycles are shown in the following
figures.
N N o o t t e e : : For purge systems equipped with standard
pump-out compressors, operation at low chiller
condenser saturation temperatures may result in
a system vacuum greater than the pump-out
compressor can overcome. If the chiller
experiences low condensing temperatures, then
the Tracer ® UC800 controller can be
programmed to inhibit the operation of the
purge pump-out compressor.
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