Trane PRGD series, Installation, Operation And Maintenance Manual

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PRGD-SVX01F-EN 21
before making a decision to shut down the chiller for
leak testing and repair.
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-123-equipped chiller is
considered to be fully saturated after the purge has
accumulated 500 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-123-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 continued stable operation of the chiller
is always more important than the regeneration of the
carbon tank. Therefore, the following rules apply:
1. If the Daily Pump-out Limit is disabled, a
regeneration cycle may not be initiated, regardless
of the value of the remaining carbon capacity.
Also, if the Daily Pump-out Limit is disabled during
a regeneration cycle, the regeneration cycle must
be terminated.
2. When the remaining carbon capacity is less than
80 percent, a regeneration cycle will be initiated at
the next opportunity when the chiller is running
(after the chiller has started and no pump-out
minutes have accumulated for the previous
60 minutes).
3. If there is no opportunity to purge as indicated by
Rules 1 and 2 and the remaining carbon capacity is
less than 50 percent, a regeneration cycle will be
initiated at the best opportunity when the chiller is
shut down (and no pump-out minutes have
accumulated for the previous 60 minutes).
4. If there is no opportunity to regenerate as indicated
by Rules 1, 2, and 3 and the carbon capacity drops
below 0 percent, then a regeneration cycle is
initiated.
5. Note that, if at any time during the regeneration
cycle the chiller is running and shuts down or if the
chiller is off and starts up, then the regeneration
cycle is continued.
Carbon Tank Regeneration Sequence
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If the purge controller determine that carbon tank
regeneration is desired and is allowed, the purge
controls:
1. Disable the purge refrigeration circuit and the
pump-out solenoid valve.
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