CleaverBrooks CFC-500 Operation, Service And Parts Manual page 146

CB FALCON
Demand and Rate
The Demand and Rate subsystem produces 3 outputs:
• Pump demand
• Burner demand, which tells the burner control it should fire,
and
• the modulation rate, which is the burner's firing rate.
There are three normal sources that share use of the burner:
• Central Heating (CH) or Steam
• Domestic Hot Water (DHW) hydronic only
• Lead Lag (LL)
These are all similar in that:
• Their inputs are a temperature sensor (pressure for steam)
and a setpoint value.
• Their outputs are:
a. On/off pump demand
b. An on/off demand indication that is on if the subsys-
tem wants the burner to fire.
c. A modulation rate which is a percentage value
between 0% and 100% that the subsystem wants as
the burners firing rate.
• They use a PID calculation to set the modulation rate.
Each of these sources has its own separate parameters.
Additionally the Falcon hydronic has two sources that can call
for burner firing, but do not use a PID calculation or modulate
to a setpoint: CH Frost Protection and DHW frost protection,
which always fire at the minimum modulation rate.
PID Requirements as a replacement for
MCBA Control:
The internal gain scalers for P, I, and D can be calibrated so
that the gains for a legacy MCBA control can be copied to the
Falcon without conversion at one specific maximum fan speed.
750-265
The chosen fan speed for calibrating these scalers is 5000
RPM, that is, when both the MCBA and the Falcon have a
maximum fan speed of 5000 RPM, the user-programmable P,
I, and D gains used by the MCBA can be directly copied to the
corresponding Falcon parameters, and the behavior of the
Falcon control will then be similar to the MCBA.
At other values of maximum fan speed, the parameters to
provide similar behavior can be calculated as:
GAIN = GAIN
FALCON MCBA
Demand/Rate Selection and Limiting
(example using Falcon Hydronic Control)
These sources of demand and modulation rate are processed
by a priority selector that determines which of the sources
(Central Heating [CH], Domestic Hot Water [DHW], or Lead
Lag Master [LL]) actually has control of the burner.
The frost protection source has control only if none of the
others want the burner to fire.
Additionally, the modulation rate requested by the source can
be modified by rate limiting, which adjusts the burner firing rate
during special conditions and it can be overridden by manual
control or burner control (e.g. prepurge and lightoff).
The descriptions of the parameters shown in Fig. 5 occur
elsewhere in this document:
• The enables and the DHW priority timeout are in "Burner
Control Operation" on page 64.
• Manual Rate control is in "Modulation Output" on page 50.
• Frost Protection is in "Frost Protection (Hydronic only)" on
page 40.
• Various Rate Limiting inputs are in "Rate Limits and
Override" on page 43.
The Demand/Rate Selection subsystem is connected internally
in the Falcon as shown in Fig. 5:
22
* Max_fan_speed / 5000