OPTIONAL FEATURES
HeatNet Control REV 1.38-1
Page 26
when a contact is closed across this input. This can be used as
a Domestic Hot Water demand input.
Another function of the OUTDOOR RESET is the
Winter/Summer mode ( (W)arm (W)eather (S)hutdown).
With the WWS SETPOINT set to 72F and WARM
WEATHER SD set to ON, the boiler/system will enter
summer shutdown when the Outside Air temperature rises
above 72F. While in this state, the OR OVR input on J12A
can be used to bring the boiler/system on to maintain the
water setpoint at the LOCAL or SYSTEM SETPOINT value.
During WWS operation, the System pump will not be enabled
just the Local pump unless the SETUP:SYSTEM
PUMP:OVR ENAB IN WWS is set to ON. This is the System
Pump priority mode. When SETUP:SYSTEM PUMP:OVR
ENAB IN WWS is set to OFF, the system pump will not
come on while in WWS with the OR OVR override input
closed.
Sensors
The Smith HeatNet control supports a standard 10K
thermistor (Type ACI/10K-CP). These sensors can be
calibrated to the control by entering the sensor menu and
placing a precision 10k resistor on an input.
Immersion sensors must have wells.
Security
A password can be used to lock out control and setup features.
It can be enabled, but is shipped in the disabled state.
Diagnostics
The Smith HeatNet control can display and identify faults in a
meaningful way. If an interlock trips, it will be indicated in
the main screen display, along with an audible alarm
(mounted on control board) and a set of relay contacts will
close. A record of this, with a time stamp, will also be entered
into the log as an aide in the diagnosis of the event. The log
can be downloaded and a histogram used to display the data.
If using Modbus, BACnet, or LonWorks, software flag bits in
registers are available.
Open and shorted sensors are checked continuously, so that in
the event of a sensor failure, the system shuts down and the
alarm relay is closed.
If a pump fails (flow switch required), or the flow switch
fails, the boiler will cycle the start condition every 10 minutes
in an attempt get the boiler restarted.
The damper fails to open and never closes its proof switch, a
retry algorithm will attempt a retry. Every 10 minutes the
damper relay will cycle and try to open the damper again.
If the H-Net control closes the last interlock string connected
to the ignition control and the ignition control never closes its
Blower Relay, the H-Net control will wait 2 minutes. The H-
Net control will then retry for the duration of the local pump
post purge time and then retry the ignition sequence. During
this time “retry strt” will be displayed in the status screen.
After (5) attempts the H-Net control will lock out and display
call service.
Communications
The Smith HeatNet control has the ability to communicate
using the MODBUS protocol with a building management
system. Most registers and functions are available for
MODBUS access. Access is allowed using the RS485
MODBUS PORT connecter.
An optional BACnet or LonWorks bridge module can be used
to connect the MODBUS network to a BACnet or LonWorks
network.
See Heating Method 5 control
.
Failsafe Modes
Failsafe Modes have been added to help protect systems from
no heat conditions. When using one of these modes
ensure
that you connect any DAMPER control, or system pump
control to safely allow operation
with the assumption that
the MASTER boiler or BMS system is DOWN
. (See Figures
35 and 36)
FAILSAFE REQUIREMENTS:
1. Since the Member boiler that will be assigned the
Failsafe duty will always turn the system pump ON, this
boiler should not be used for DHW heating. If the Master
controls the system pump, then the Failsafe Member
boiler would need to control the system pump in parallel
with the Master boiler. Wire the System Pump contacts in
parallel with the Master.
2. If the combustion air damper is used as a common system
damper, the Failsafe boiler should be wired to control the
damper in parallel with the Master boiler.
3. The Failsafe boiler should have the LOCAL SETPOINT
set to the same setpoint temperature as the Master
boiler’s SYSTEM SETPOINT.
Be aware that the boiler may start without a call-for-heat
in the FAILSAFE MODES
. FAILSAFE MODES can be
accessed through the:
SETUP:AUX FUNCTIONS:FAILSAFE MODES
