Modulating Stage, Overflow and Underflow

the LL master is not asking for less heat than this, then the underflow rate is 0%. If it is at this location and the LL master is asking for 10% less than the threshold value, then the underflow rate is -10%. If the last stage is 5% above the threshold then the underflow rate is 5%.

Rate allocation methods

PARALLEL COMMON BASE LIMITED Allocation

All stages that are Firing receive the same firing rate.

Only the Base load common parameter is used for base loading, the individual slave's base load values are ignored.

As load increases:

Until all stages are Firing:

No stage is requested to exceed the common base load rate.

After all stages are Firing:

There is no restriction on the slave's commanded firing rate.

As load decreases:

As long as all available stages are Firing There is no restriction on the slave's commanded firing rate.

When at least one stage has been dropped:

No stage is requested to exceed the common base load rate.

MODULATING STAGE

Since all Firing stages receive the same rate, any stage can be considered to be the modulating stage. The one with the highest StagingOrder number is considered to be the modulating stage.

Last stage

The stage with the highest StagingOrder number is the last stage.

OVERFLOW AND UNDERFLOW

For the Parallel common-base limited the Base load common parameter provides the overflow threshold.

Date: 8-4-2010

Revision: 0

Form: 2396

For the Parallel common-base limited the minimum modulation rate provides the underflow threshold.

Stager

The Stager is an internal program that determines when slave Solas should turn on as the need for heat increases, and when they should turn off as the need for heat decreases.

In all cases:

•The first burner turns on due to the combination of heat demand (call for heat) and setpoint demand (operating point falls below the setpoint minus the on hysteresis).

•The last burner (or all burners) turn off due to the loss of burner demand which is caused by either the loss of heat demand (no call for heat) or the loss of setpoint demand (the operating point climbs above the setpoint plus the off hysteresis).

•In between those two extremes the Add-stage and Dropstage methods determine when staging occurs. The stager handles burner on and burner off events. It operates according to this state transition diagram.

The stager has the following variables: StagerState: encodes the current state of the stager.

StagerTimer: multipurpose 1 second timer used by states which measure time. StagerTimeLimit: the timeout value for the StagerTimer

LeadStartup: flag indicating the lead boiler is starting

AddStageA: the stage being added to those already firing

Stager Parameters

ADD-STAGE INTERSTAGE DELAY: MM:SS This specifies the minimum time that the Stager waits after adding one stage before adding another stage or dropping a stage.

DROP-STAGE INTERSTAGE DELAY: MM:SS This parameter specifies the minimum time that the Stager waits after dropping one stage before dropping another stage or adding a stage.

Functions common to all stager states

These functions handle overall burner demand responsibility, and take care of cleaning up any anomalous conditions.