Bryan Boilers & 300 DROP-STAGE Error Threshold Degrees, DROP-STAGE Rate Offset -100% to +100%

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.

LLboiler 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.

LLALL 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

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Date: 8-4-2010

Revision: 0

Form: 2396

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

LLall 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