OPTIONAL FEATURES
HeatNet Control REV 1.38-1
Page 21
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 Method 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 that it has 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 15
Heat Demand Input
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 or 0-10VDC signal by each boiler. The
temperature of the water is maintained by sending this signal
to the Mod Motor, which in turn controls the damper position
and fuel rate. providing the firing rate control.
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
proper use of a Common System Damper (See:
AUXILIARY
FUNCTION OPTIONS
section) and any system pumps or
system common interlocks.
Features of the HEAT DEMAND input include:
1.
The control is designed to
predict
when to start and
stop the boiler and keep the setpoint in, or as close to
the control band as possible. If PREDICTIVE
START is enabled, the boiler may start when it is in
the band and not below it. This will help to maintain
a more accurate temperature relative to the setpoint.
See also: ADVANCED SETUP:FIRING
MODE:PRDICTIVE START: to disable this feature.
2.
The control can also use the Outdoor Reset feature.
This feature allows the setpoint to be changed
automatically based on the outside air temperature. If
this feature is used, the control input: OR OVR
(OUTDOOR RESET OVERRIDE), can be used to
override the Outdoor Reset feature and run from the
local setpoint. A contact closure on the ‘AA’ input
can also override this method.
3.
The Setpoint can be controlled remotely using the 4-
20ma setpoint control function.. This function translates a
4-20ma control signal to a setpoint mapped between 50F
and 220F. These (2) temperatures are adjustable to
provide a setpoint range. The minimum start current is
also adjustable between 3.71 and 5ma. The setpoint
control feature is used in conjunction with the REMOTE
ENABLE input on J12A. This feature is enabled in the
SETPOINTS menu as:
SETPT SOURCE 4-20ma
MASTER: Close contact to control all boilers and run at system setpoint.
MEMBER: Close to run at LOCAL setpoint
