OPTIONAL FEATURES
HeatNet Control V3 3.x
Page 76
In order to provide a means of controlling these situations and
preventing downtime, the HeatNet control allows a relay to
control the power fed to the blower. This is done by wiring
the 120 VAC power to the J13A.1 Stage 4 relay contact using
black 18-gauge MTR/TEW wire. Then wiring (same wire
type) from J13A.2 to the Ametek blower contactor’s enable
input. This allows the HeatNet control firmware to control
power to the blower by switching the contactor ON or OFF.
The reasons for this are as follows:
1.
The Stage 4 relay has been allocated to help bring the
power up in steps. These steps are used to minimize
inrush currents by engaging the blower’s contactor (7)
seconds after the main power has been applied.
2.
In the event a blower lockout has been determined, a
(10) minute retry cycle, (3) times will occur. At the time
the blower has been detected as locked out, the retry
cycle will start. The Stage 4 relay will be de-energized
for (8) minutes. Then the Stage 4 relay will be energized
for (2) minutes. This will effectively power cycle just
the blower. The call for heat will then be allowed to start
the boiler. After (3) failed retry attempts, the boiler will
lock out.
Communications
The H-Net control, using the standard MODBUS protocol,
can communicate with a building management system. Most
registers and functions are available for MODBUS access.
Access is allowed using the RS485 MODBUS PORT
connecter on the communication board. Version 3.x Control
has these connections integrated on the main board.
An optional BACnet or LonWorks bridge module can be used
to connect the MODBUS network to a BACnet or LonWorks
network. See Method 5 control.
Failsafe Modes
FAILSAFE MODES have been added to help protect systems
from loss of 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.
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 must 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
.
The following are types of Failsafe conditions.
1.
Building Management System Failure
If a BMS system is controlling the setpoint and enabling
the boiler system, a timer is provided to allow operation
of the system in the event that communications are lost
with the BMS system. The HeatNet boiler system will
run locally if communication is lost, and this timer
expires due to the lack of being updated.
The system setpoint timer and system setpoint work in
tandem to externally control (i.e., a BMS - building
management system) the operating setpoint. The setpoint
(countdown) timer should be loaded with a timeout value
(in seconds) prior to writing the system setpoint. When
the timer reaches zero, the control assumes that the BMS
is no longer operating and the local setpoint (saved on the
control) is reloaded. If the setpoint timer is not written, a
default timeout value of 60 seconds is assumed. The
timer is automatically reloaded with the default value
when a setpoint is written.
The BMS mode is always on, and no menu
item is available.
2.
HeatNet Communications Lost
SETUP: AUX FUNCTIONS: FAILSAFE MODES: H-
NET COMM LOST
:
This mode allows a MEMBER boiler to run in LOCAL if
the communications link via the H-NET cable is lost.
This includes the MASTER boiler losing its Control
board, Communications board, or the power on the
MASTER is switched OFF. When this MODE is set to
ON, and if the MEMBER boiler loses its link (heartbeat
packet over the H-NET cable) to the MASTER Boiler,
this MEMBER will fire to the LOCAL setpoint.
The heartbeat packet over the H-NET cable
needs to be lost for 10 minutes.
This MEMBER boiler will continue to run at the LOCAL
setpoint until H-NET communications from the
MASTER boiler is re-established.