Rate Allocation, Base Load Common 0-100% | Bryan Boilers & 300, 250

Lead Lag burner demand will be present when Frost protection burner demand is true, as described in the section on Frost protection. For the CH, and DHW demand sources, Lead Lag burner demand will be true when one of these is true and also setpoint demand from the hysteresis block is true.

4.7.9RATE ALLOCATION

The PID block's output is used to determine the firing rate of each slave Sola using various rate allocation techniques.

Common Features

All rate allocation methods share certain features. The rate allocator first generates the Slave Command. Except for the Firing state, the value ultimately depends only upon the SlaveState. The values are:

Available

AddStage

SuspendStage depending on whether any other slave stage is firing, no matter what SlaveState it is in.

Firing

OnLeave - same as SuspendStage

This ensures that when a slave returns and is already firing, it will remain firing until the master decides what to do about that, or if it is not firing it will remain off.

Disabled - same as Available Recovering - same as Available

It next runs a rate allocator that depends upon the rate allocation method. This routine fills in the modulation rate for all Firing boilers.

Each rate allocation method also provides functions to return identification of the modulating stage and the last stage, for use by the Add-stage and Drop-stage methods.

Rate Allocation Parameters

BASE LOAD COMMON: 0-100%

If set to zero, this parameter is disabled. For any non-zero value, it uses the individual base load rates of each slave to be ignored by the LL master's routines and this common value to be used instead. It is an easy way to set all base loads to the same value, without having to set

Date: 8-4-2010

Revision: 0

Form: 2396

each slave. Some rate allocation algorithms may specify the use of this parameter, and that the slave base load settings are ignored.

RATE ALLOCATION METHOD: PARALLEL COMMONBASE LIMITED

This selects the rate allocation method. This performs three purposes:

it determines how the LL master allocates firing rate to each active stage,

the modulating stage and last stage are determined for the Add-stage and Drop-stage methods,

it determines the overflow rate and underflow rate and can provide this to staging algorithms.

OVERFLOW RATE AND UNDERFLOW RATE The rate allocator knows the rate assigned to each stage, and the requested rate, and thus can determine the difference between these.

This difference has two forms: overflow (used by Addstage methods), underflow (used by Drop- stage methods).

When asked for rate overflow the threshold that is used is the upper limit of the modulating stage per the current rate allocation rules. Additionally this threshold may be shifted if the Add-stage method is using a dRate/dt behavior. Rate overflow is a positive or negative percentage offset from the threshold. For example:

If the modulating stage is at the staging threshold position but the

LLmaster is not asking for more heat than this, then the overflow rate is 0%. If it is at this location (limited) or above this location (unlimited) and the LL master is asking for 10% more than the threshold value, then the overflow rate is 10%. If it is below the staging threshold position by 5%, then the overflow rate is -5%.

When asked for rate underflow the threshold that is used is the minimum modulation rate of the last stage. Additionally this threshold may be shifted if the Dropstage method is using a dRate/dt behavior.

Rate underflow is a positive or negative percentage offset from the threshold. For example:

If the last stage is at the threshold position but