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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)
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.
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:
• 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.
Note: 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 Symbio™ 800 controller can
be programmed to inhibit the operation of the purge
pump-out compressor.
Carbon Tank and Regeneration
Subsystem
The function of the carbon tank is to absorb refrigerant
molecules that may be entrained in the discharge of non-
condensables. In order to maintain effectiveness, the
carbon tank periodically regenerates.
Carbon Regeneration Algorithm
The controller uses the carbon regeneration algorithm to
determine when to initiate, control, and terminate a carbon
regeneration cycle. The carbon bed temperature sensor
serves as the feedback to this algorithm. In addition, the
controller uses a pump-out accumulation timer to indicate
the remaining carbon capacity in the carbon tank. The
carbon capacity is the capacity of the carbon to adsorb
refrigerant while maintaining acceptable levels of
refrigerant emission through the chiller vent line. A capacity
of 100 percent means the carbon bed has the capacity to
adsorb refrigerant and maintain acceptable emission
levels. A capacity of 0 percent means the carbon bed has
inadequate capacity to adsorb refrigerant and still maintain
acceptable emission levels.
The main objectives of the carbon regeneration algorithm
are to:
• Minimize the amount of refrigerant contained in the
carbon by performing a periodic regeneration.
• Regenerate to maintain low emissions levels.
• Minimize the regeneration time.
• Regenerate only when the chiller is at a minimum level
of purging activity.
• Allow regeneration to occur with the chiller On or Off.
Regeneration is preferable when the chiller is On to
ensure low carbon tank pressure, but regeneration is
also acceptable when the chiller is Off.
The remaining amount of adsorption capacity within the
carbon tank is directly proportional to the number of purge
pump-out minutes that have accumulated, and is also a
function of the chiller refrigerant type. The purge carbon
tank on an R-1233zd-equipped chiller is considered to be
fully saturated after the purge has accumulated
350 minutes of pump-out time. Because the relationship
between pump-out capacity and pump-out minutes is
directly proportional, it can be described by the following
equation within the regeneration algorithm:
Remaining carbon capacity% =
100 - (pump-out minutes since last regen/pump-out
minutes at 100% capacity)*100
For example, an R-1233zd-equipped chiller that has
accumulated 80 minutes of purge pump-out time since the
last carbon tank regeneration would be estimated to have
84 percent carbon tank capacity remaining:
100 – (80/500)*100 = 84%
The purge controls may initiate a carbon tank regeneration
cycle when the remaining carbon tank capacity is
calculated to be less than 80 percent. However, the
Start-up and Shutdown
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