Bryan Boilers 250, & 300 ADD-STAGE Error Threshold Degrees, ADD-STAGE Rate Offset -100% to +100%

Stager can execute an AddStage or DropStage request.

Add Stage Methods

Various methods can be used to determine when a new stage should be added. The internal algorithms that generate AddStageRequests are called Add-stage methods.

All methods work by observing various criteria such as the Firing stages, the commanded rate, or setpoint error.

Adding Stages Parameters:

ADD-STAGE DETECTION TIME1: MM:SS This provides time thresholds.

In the descriptions below, the relevant parameter is referred to as Add-Stage detection timeN.

Add-Stage method1: Disable,

Error threshold, Rate threshold, dError/dt and threshold, dRate/dt and threshold }

In the descriptions below, the relevant AddStageDetect- Timer is referred to as AddStageDetectTimerN.

ADD-STAGE ERROR THRESHOLD: DEGREES

This provides the error threshold as defined by the methods below.

ADD-STAGE RATE OFFSET: -100% TO +100%

This provides the rate offset threshold as defined by the methods below.

Add-stage methods

ERROR THRESHOLD

For error threshold staging, a stage is added when the error becomes excessive based on degrees away from setpoint, and time.

ADD-STAGE CONDITION:

-The modulating burner(s) is at its (their) maximum position per the rate allocation rules,

-The operating point is below the setpoint by an

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Date: 8-4-2010

Revision: 0

Form: 2396

amount greater than or equal to Add-stage

error threshold

When the Add-stage condition is false then AddStage- DetectTimerN is set to zero. (If the condition is true then AddStageDetectTimerN is not zeroed and thus allowed to run.) If this timer reaches or exceeds LLAdd- stage detection timeN then AddStageRequestN is true.

RATE THRESHOLD For rate based staging, a stage is added based on the rate of the modulating stage.

ADD-STAGE CONDITION:

The modulating burner is at a rate that is at or above the rate which is calculated by adding the Add-stage rate offset to the maximum position per the rate allocation rules.

Examples: rate offset = 20% The add-stage condition will occur if the modulating stage is 20% above base load for unlimited allocations, or, if limited, when there is 20% more rate to distribute than can be absorbed by firing the stages at base load.

rate offset = -20% The add-stage condition will be as described just above, but the threshold is now 20% below the modulating stage's base load rate.

To support this, the current Rate Allocation method asks for the current "Overflow rate" - see the Rate Allocator section.

Drop Stage Methods

Various methods can be used to determine when a stage should be dropped. The internal algorithms that generate DropStageRequests are called Drop-stage methods.

One or two methods may be active at any time. If two are active then their requests are OR'd together.

All methods work by observing various criteria such as the Firing stages, the commanded rate, or Setpoint.

Dropping Stages Parameters:

DROP-STAGE DETECTION TIME: MM:SS This provides time thresholds. They differ only in