OPTIONAL FEATURES
HeatNet Control REV 1.38-1
Page 31
DHW METHOD 4: DHW using
Direct Control
The 4-20 mA input can be set to the HIGH(est) PRIORITY.
This can be set in menu:
ADVANCED SETUP:4-20mA
INPUT
. This allows a member boiler to be taken offline and
directly modulated by an external control.
If the Master is using it for heating and the 4-20mA is
set to HIGH PRIORITY, an external control can now
output a 4-20mA signal which will take over the
boiler’s fire rate and override all other heating
demand inputs. This is typically used for DHW
control.
Dual Fuel Option
The OPTION control input allows for optional functions. This
input designated as the ‘OPTION” input (J12B terminals 5 &
6) can be used as a programmed input. The menu:
ADVANCED SETTINGS:SYSTEM:OPTION,
can be used to set the DUAL FUEL option if equipped. It
assigns the K8 relay contacts on J4.1 &.2 to this function if
not using the Base Load Option.
The Dual Fuel option functionality is the same for a Master or
Member.
1.
When the Option input switch is open, the Solid State
Relay (K8) has its contacts open on J4, between pins 1
and 2. FUEL 1
2.
When the Option input is closed, the control detects a
change on this input and stops the boiler (if running).
3.
Once the boiler stops, K8’s contacts close. This allows
the Fuel relay to energize and change the fuel. The
message FUEL CHNG will be displayed in the Status
Line. FUEL 2
4.
If there is still a call for heat, the boiler restarts.
5.
If the Option input now opens, the change is detected and
the cycle repeated.
Stack Temperature
The Smith HeatNet control monitors the stack temperature
and sets a warning or an alarm message in the event that
the Stack Temperature exceeds a predefined threshold. The
Stack Temperature is monitored since it is a good indicator
of the boilers health. The sensor that measures this
temperature is a 1k ohm RTD type sensor which can
handle the higher temperatures of the flue gas.
A
warning
message appears when the Stack Temperature
exceeds 550F. The Alarm relay does not close and no
action is taken. The message is the only indication. Service
is usually required or needs to be scheduled (cleaning and
checkup).
An
alarm
message appears when the stack temperature
exceeds 700F. The alarm contact also closes to indicate a
problem with the boiler. The next thing that happens is the
boiler
is limited to firing at ½ it’s called for rate
. In
order to clear the alarm condition the Stack temperature
must fall below the warning temperature of 550F. This will
also remove the firing rate limit restriction.
A high Stack Temperature indicates that heat energy from
the combustion process is not being transferred efficiently
to the water. Overall boiler efficiency is reduced and
damage to the boiler could result. At this point action
should be taken immediately to correct the problem.
An additional function has also been included
to help protect the boiler. AUX
FUNCTIONS:HEAT EXCHANGER:LOW
TEMP HOLD is used to hold the boiler at the
low fire rate until the return temperature
exceeds the set value. The default is 130F, but
can be increased to 160F
Interlock Selection
The Smith HeatNet control allows selection of interlocks
to monitor. An interlock can be monitored by connecting a
wire from the point after the interlock to the appropriate
terminal on J5 of the control board.
Figure 25
Interlocks
As an example: To connect the Local Water Flow switch to J5
first identify the normally open contact on the flow switch.
Next, attach a wire to this point. Now, run the wire through a
rigid conduit to the control and connect the wire to “J5B,
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