Appendix E Falcon Lead Lag
E-55
• An add-stage is in-progress and all firing burners are at their limits (max modulation rate or base load) and then
the new stage becomes available.
This also applies when the system is first starting up, that is, all firing burners are at their limits (zero) because non
are firing, and thus when the add-stage is finished the system transitions from no modulation at all, to modulating
the first stage.
Lead Lag Burner Demand
Lead Lag burner demand will be present when Frost protection burner demand is true, as described in the section
on Frost protection. For the CH, and DHW demand sources, Lead Lag burner demand will be true when one of
these is true and also setpoint demand from the hysteresis block is true.
Rate Allocation
The PID block's output is used to determine the firing rate of each slave using various rate allocation techniques.
Common Features
All rate allocation methods share certain features.
The rate allocator first generates the Slave Command. Except for the Firing state, the value ultimately depends
only upon the SlaveState. The values are:
Available
AddStage
SuspendStage depending on whether any other slave stage is firing, no matter what SlaveState it is in.
Firing
OnLeave - same as SuspendStage
This ensures that when a slave returns and is already firing, it will remain firing until the master decides what to
do about that, or if it is not firing it will remain off.
Disabled - same as Available
Recovering - same as Available
It next runs a rate allocator that depends upon the rate allocation method. This routine fills in the modulation rate for
all Firing boilers.
Each rate allocation method also provides functions to return identification of the modulating stage and the last
stage, for use by the Add-stage and Drop-stage methods.
Rate Allocation Parameters
BASE LOAD COMMON: 0-100%
If set to zero, this parameter is disabled. For any non-zero value, it uses the individual base load rates of each slave
to be ignored by the LL master's routines and this common value to be used instead. It is an easy way to set all
base loads to the same value, without having to set each slave.
Some rate allocation algorithms may specify the use of this parameter, and that the slave base load settings are
ignored.
RATE ALLOCATION METHOD: PARALLEL COMMON-BASE LIMITED
This selects the rate allocation method. This performs three purposes:
1) it determines how the LL master allocates firing rate to each active stage,
2) the modulating stage and last stage are determined for the
Add-stage and Drop-stage methods,
3) it determines the overflow rate and underflow rate and can provide this to staging algorithms.
OVERFLOW RATE AND UNDERFLOW RATE
The rate allocator knows the rate assigned to each stage, and the requested rate, and thus can determine the
difference between these.
This difference has two forms: overflow (used by Add-stage methods), underflow (used by Drop-stage methods).
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