MODEL FIII-SERIES CONTROL INSTALLATION ... - Agencespl.com

REV 1.1
FIII SERIES CONTROL
Setup & Operation
Control Methods
There are (5) methods for controlling the FIII series
boiler. See Figures 1 through Figure 8.
1. The first method is to use the FIII series boiler in
its stand-alone modulating method (Local
Control). This method uses a PID algorithm to
maintain a setpoint and is enabled using the
HEAT DEMAND input. (Closing a relay contact
or switch across the HEAT DEMAND input
causes the Master to control all boilers, a
member would control itself using the its supply
sensor)
2. The second method is to view the FIII boiler as
four separate boilers, firing at (4) predetermined
rates using the T1, T2, T3, and T4 inputs (stage
control).
3. The third method is to allow a remote 4-20 ma or
0-10 VDC signal to control the firing rate
(modulation) of the boiler using the 4-20ma
input, along with the 4-20ma REMOTE
ENABLE input.
4. The fourth method turns the boiler ON and OFF
@ 100% modulation using the AA terminal.
5. The fifth method uses an RS485 digital
communications cable with the MODBUS
protocol to control the boiler. Writing and
reading registers using MODBUS commands.
When the master boiler or an external control input is
used to control a member boiler (i.e. AA, T1-T4, 4-20ma,
H-Net), a software operating limit on the member boiler
will be used to limit the maximum output of the member
boiler. This operating limit can be adjusted in the
SETPOINTS menu under OPERATING LIMIT. There is
also an associated operating limit band that must be set in
conjunction with the operating limit to help prevent this
LIMIT from being reached. It’s purpose, is to limit the
output of the boiler as it approaches the operating limit. If
the band is set to 10 degrees, then for every degree that it
approaches the operating limit, the maximum output will
be lessened by 10%. With a band of 20 degrees, for every
degree that it approaches the band, the maximum output
will be lessened by 5%. This method minimizes boiler
short cycling when using external inputs. The minimum
setting is 1 degree and effectively turns the limit band
OFF.
The FIII series control inputs are prioritized so that
multiple levels of external control can be employed at
the same time. This means that if we are firing the
boiler with a low priority input and a higher priority
input is called for, the boiler will now fire at the higher
priority input. When the high priority input is removed,
the boiler will revert back to the lower priority input
that is still being called.
Priority 1.
Priority 2.
Priority 3.
Priority 4.
Priority 5.
The AA terminal has absolute
control, and if used, will always
fire the boiler at 100% output,
regardless of any other input.
The HEAT DEMAND input is the
next, and provides the means to
operate the boiler in LOCAL
CONTROL when an external
control is not present, has failed, or
needs to be enabled or disabled. A
member can override the H-Net
commands using this input.
If a Heat Net (H-Net) Network
cable is connected between boilers,
and one is configured as a
MASTER (requires HEADER
sensor), then the MEMBER boilers
will be controlled over the network
by the MASTER.
The 4-20ma/0-10VDC input in
tandem with the 4-20ma REMOTE
ENABLE input is next. Any signal
over 4.02ma or 2.01VDC will start
and operate the boiler if the
REMOTE ENABLE is closed.
The lowest priority is using the
boiler as (4) stages. These are the
T1, T2, T3, and T4 inputs.
Each of these control methods will now be explained in
more detail:
1. AA Input; HIGH FIRE input Control: The AA
input will fire the boiler at HIGH fire (maximum
output of the boiler). No other inputs can
override this input.
2. LOCAL Control: Closing a contact across the
HEAT DEMAND input starts the boiler. Once
the boiler is started, a PID algorithm is used to
produce a PWM, (P)ulse (W)idth (M)odulation
signal. This signal is used to regulate the boilers
output based on a LOCAL setpoint or a setpoint
derived from an outdoor reset ratio. The
temperature of the water is maintained by
sending this modulating signal to the Variable
Frequency Drive, which in turn controls the
blower motor. Since the main fuel valve is airfuel
coupled to the blower, the speed of the
blower provides the firing rate.
The Local Control includes short cycling
compensation of the PID. When the boiler is
running with a minimum load, a short cycling
condition may exist that will cause the water
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