Falcon Lead Lag Appendix E
E-56
When asked for rate overflow the threshold that is used is the upper limit of the modulating stage per the current
rate allocation rules. Additionally this threshold may be shifted if the Add-stage method is using a dRate/dt
behavior. Rate overflow is a positive or negative percentage offset from the threshold. For example:
If the modulating stage is at the staging threshold position but the
LL master is not asking for more heat than this, then the overflow rate is 0%. If it is at this location (limited) or
above this location (unlimited) and the LL master is asking for 10% more than the threshold value, then the
overflow rate is 10%. If it is below the staging threshold position by 5%, then the overflow rate is -5%.
When asked for rate underflow the threshold that is used is the minimum modulation rate of the last stage. Addi-
tionally this threshold may be shifted if the Drop-stage method is using a dRate/dt behavior.
Rate underflow is a positive or negative percentage offset from the threshold. For example:
If the last stage is at the threshold position but the LL master is not asking for less heat than this, then the
underflow rate is 0%. If it is at this location and the LL master is asking for 10% less than the threshold value,
then the underflow rate is -10%. If the last stage is 5% above the threshold then the underflow rate is 5%.
Rate allocation methods
PARALLEL COMMON-BASE LIMITED
Allocation
All stages that are Firing receive the same firing rate.
Only the Base load common parameter is used for base loading, the individual slave's base load values are
ignored.
As load increases:
Until all stages are Firing:
No stage is requested to exceed the common base load rate.
After all stages are Firing:
There is no restriction on the slave's commanded firing rate.
As load decreases:
As long as all available stages are Firing There is no restriction on the slave's commanded firing rate.
When at least one stage has been dropped:
No stage is requested to exceed the common base load rate.
MODULATING STAGE
Since all Firing stages receive the same rate, any stage can be considered to be the modulating stage.
The one
with the highest StagingOrder number is considered to be the modulating stage.
Last stage
The stage with the highest StagingOrder number is the last stage.
OVERFLOW AND UNDERFLOW
For the Parallel common-base limited the Base load common parameter provides the overflow threshold.
For the Parallel common-base limited the minimum modulation rate provides the underflow threshold.
Stager
The Stager is an internal program that determines when slave CB Falcons should turn on as the need for heat
increases, and when they should turn off as the need for heat decreases.
In all cases:
• The first burner turns on due to the combination of heat demand (call for heat) and setpoint demand (operating point
falls below the setpoint minus the on hysteresis).
• The last burner (or all burners) turn off due to the loss of burner demand which is caused by either the loss of heat
demand (no call for heat) or the loss of setpoint demand (the operating point climbs above the setpoint plus the off
hysteresis).
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