Appendix E Falcon Lead Lag
E-61
LL ALL BOILERS OFF THRESHOLD: TEMPERATURE OR NONE
When the LL boiler off options specifies "Enable all boilers off (ABO)" or "Enable both ABO and LDSE" then this
parameter provides the boiler off threshold temperature that is used. In this case, if the temperature is the None
value then a parameter error lockout occurs.
Drop-stage methods:
Error threshold
For error threshold staging, a stage is dropped when the error becomes excessive based on degrees away from
setpoint and time.
DROP-STAGE CONDITION:
- The modulating burner(s) is at its (their) minimum position per the rate allocation rules,
- The operating point is above the setpoint by an amount greater than or equal to Drop-stage error threshold
When the Drop-stage condition is false then
DropStageDetectTimerN is set to zero. (If the condition is true then
DropStageDetectTimerN is not zeroed and thus allowed to run.) If this timer reaches or exceeds Drop-stage
detection timeN then DropStageRequestN is true.
Rate threshold
For rate based staging, a stage is dropped based on the rate of the last stage.
DROP-STAGE CONDITION:
-The modulating burner(s) is at a rate that is at or below the minimum modulation rate plus a rate offset.
Examples:
rate offset = 20% The Drop-stage condition will occur when the last stage is less than a threshold that is the
minimum modulation rate plus another 20%.
rate offset = 0% The Drop-stage condition will occur when the last stage is at the minimum modulation rate.
rate offset = -20% The Drop-stage condition will occur if the last stage is at minimum modulation and there is
20% less rate to distribute than can be absorbed; that is, the rate allocator would like the minimum modulation
rate to be lower than it is.
To support this, the current Rate Alloction method asks for the current "Underflow rate" - see the Rate Allocator
section.
Boiler off options
The LL boiler off option controls two optional behaviors. One option is to enable the use of the LL all boilers off
threshold and is abbreviated "ABO", and the other controls whether a lead boiler is affected by a drop-stage
method based upon error, and is abbreviated as "LDSE".
ALL BOILERS OFF - ABO:
The ABO temperature provides a Burner Off threshold that essentially replaces the normal Burner Off threshold as
given by the LL off hysteresis parameter; it is processed by the same logic block using some additional rules.
If ABO is enabled then:
• When the LL master operating point reaches or exceeds the ABO threshold this turns off LL master burner
demand.
• The Burner Off threshold provided by LL off hysteresis is ignored if one or more lag boilers are firing.
• If LDSE is enabled:
The Burner Off threshold provided by LL off hysteresis is ignored also for the lead boiler when it is firing solo
(i.e. when no lag boilers are firing).
• If LDSE is disabled:
When the lead is firing solo and the operating point reaches the Burner Off threshold specified by LL off
hysteresis turns off LL master burner demand (and thus the lead boiler).
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