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Date: 8-4-2010
Revision: 0
Form: 2396
that:
Drop-Stage detection time is used with
DropStageDetectTimer
In the descriptions below, the relevant
parameter is referred to as LL – Drop Stage
detection timeN}.
Drop-Stage method:
Disable,
Error threshold,
Rate threshold,
dError/dt and threshold,
dRate/dt and threshold
DROP-STAGE ERROR THRESHOLD:
DEGREES
This provides the error threshold as defined by
the methods below.
DROP-STAGE RATE OFFSET: -100% TO
+100%
This provides the rate offset threshold as
defined by the methods below.
LL boiler off options:
Options disabled,
Enable all boilers off (ABO)
Enable lead drop-stage on error (LDSE)
Enable both ABO and LDSE
This provides options for customizing the way
stages are dropped, as described below.
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 Dropstage 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
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