CONTROL METHODS
HeatNet Control V3 3.x
Page 32
Input Priorities
The KN-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 to the lower
Priority input that is still being called.
Priority 1
The AA terminal has absolute control, and if used, will
always fire the boiler at 100% output, regardless of any other
input. The 4-20mA input may be raised to this Priority using
SETTINGS: 4-20mA INPUT: PRIORITY
.
Priority 2
The HEAT DEMAND input is the next and provides the
means to operate the boiler in LOCAL MODE 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.
Priority 3
If a HeatNet (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.
Priority 4
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.
Priority 5
The lowest Priority is using the boiler as (2) stages
HIGH/LOW. These are the T1 and T2 inputs.
Each of these control methods will now be explained in more
detail:
Heating Control Input 1
HEAT DEMAND
Closing a relay contact, switch, or jumper across the HEAT
DEMAND input will enable this method. This method allows
operation as a setpoint control. As a setpoint control, the
MASTER (defined by having a common system supply
header sensor), on the H-Net network can command the boiler
fire rate of all MEMBER boilers. The MASTER can call as
many boilers as are available (boilers are auto-detected over
the H-Net cable by the MASTER) to meet its
SYSTEM
SETPOINT
. The H-Net cable must be connected and will
cause the amber light on the communications board to flash.
The amber light indicates an H-Net MASTER is broadcasting
control information and a system heartbeat.
The AA terminal, the FAILSAFE mode active, 4-20mA at
PRIORITY: HIGHEST, and the HEAT DEMAND input
(LOCAL) on a MEMBER, are the only inputs that will
override the H-Net control.
Figure 21
Heat demand input
MEMBER: Close to run at Local setpoint.
MASTER: Close to control all boilers and
run at System setpoint.
MASTER boiler
The MASTER boiler controls the system using a PID
algorithm. Once the boiler is started, a PID algorithm is used
to produce a modulation percentage value from 0-100%. This
percentage is converted to a PWM, (P)ulse (W)idth
(M)odulation signal by each boiler. The temperature of the
water is maintained by sending this PWM signal to the
Variable Frequency Drive, which in turn controls the blower
motor. Since the main fuel valve is air-fuel coupled to the
blower, the speed of the blower provides the firing rate.
MEMBER boiler(s)
A MEMBER (lacking a common system supply header
sensor) boiler may also be controlled by the HEAT
DEMAND input (LOCAL mode). The MEMBER boiler will
then ignore commands from the MASTER and maintain its
own LOCAL SETPOINT at its supply sensor. This can be
viewed as a manual override on a MEMBER boiler. Be sure
to observe the use of the proper use of a Common System
Damper (See: AUXILIARY FUNCTION OPTIONS section)
and any system pumps or system common interlocks.
Figure 22
HeatNet Boilers Configured as Reverse Return
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