Falcon Lead Lag Appendix E
E-62
As usual, whenever LL master burner demand is turned off by its hysteresis block, it does not recur until the operating
point falls below the Burner On threshold.
Summary of the burner-off thresholds that are used:
LEAD DROP-STAGE ON ERROR - LDSE:
If LDSE is enabled then either Drop-stage method1 must be enabled to provide staging based on "Error thresh-
old"; otherwise a parameter error lockout occurs.
Normally, for a lag boiler, dropping a stage based on error involves meeting three criteria: 1) the operating point
temperature must exceed an offset from setpoint, 2) this condition must persist for a period of time, and 3) the mea-
sured time starts only when the modulating boilers are firing at the minimum modulation rate. And normally when
LDSE is not enabled, the lead boiler is special case that is not affected by a drop-stage event: it shuts down only
when the operating point reaches the burner-off threshold (or ABO threshold, if that is enabled).
If LDSE is enabled:
• Enabling (or disabling) LDSE has no effect on the drop-stage behavior for a lag boiler; however
• When only the lead boiler is firing then an error based drop-stage event does act to drop the lead boiler, and
moreover, only one of the three criteria above are considered by the method in this case: the operating point
temperature. Thus dropping the lead does not depend on exceeding this temperature for a period of time, nor
does it require the lead to be at minimum modulation rate. When LDSE is enabled and the lead is firing solo,
then simply reaching the drop-stage threshold causes a dropstage event that causes the lead to turn off and
[rf3259] which thus ends LL master demand until the operating point again falls to the Burner On threshold.
Sequencer
The sequencer determines which CB Falcon will be the next one to turn on or turn off whenever an Add-stage event
occurs. It maintains the following variables:
LeadBoilerSeqNum - sequence number of the current lead boiler in the Slave Status table.
Lead BoilerRunTime - the cumulative time that the current lead boiler has been running
In all cases, if a boiler sequence number is needed and Slave sequence order is 0, then the boiler's ModBus
address is used as its sequence number.
In all cases,
if two boilers being compared have the same effective sequence
number, then the one that is selected is undefined (either may prevail).
Sequencer Parameters
LEAD SELECTION METHOD: ROTATE IN SEQUENCE ORDER, MEASURED RUN TIME
This determines the selection method for lead selection and sequencing, as described below.
LAG SELECTON METHOD: SEQUENCE ORDER, MEASURED RUN TIME
This determines the selection method for lag selection and sequencing, as described below.
LEAD ROTATION TIME: HH:MM OR NONE
This determines the lead rotation time as defined below.
LDSE ABO DSE
LL Off Hysteresis All Boilers Off Thresholdenabled enabled exists
0 0 x OpPt > Off Hyst means all off Ignored (disabled)
0 1 x OpPt > Off Hyst ignored if lags exist.
OpPt > Off Hyst drops lead if it is solo.
OpPt > ABO means all off
1 0 0 Illegal, param error lockout
1 0 1 Same thresholds as "0 0 x" above.
1 1 0 Illegal, param error lockout
1 1 1 Ignored by both lags and lead. OpPt > ABO means all off
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