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WATER HEATER BUILDING MANAGEMENT SYSTEM (BMS)
1. An external control may be connected to control either the
firing rate or the set point of the water heater. If the external
control uses a set of contacts to enable the water heater,
connect the contacts to the Tank Thermostat terminals.
Otherwise, the Control Module will be enabled by the 0-10V
signal.
2. Make sure the (-) terminal is connected to the (-) or common
output terminal of the external control, and the (+) terminal
is connected to the (+) or 0 - 10 VDC terminal of the external
control. Make sure the (-) voltage is not below ground.
RUNTIME CONTACTS
The Control Module closes a set of dry contacts whenever the
burner is running. This is typically used by Building Management
Systems to verify that the water heater is responding to a call for
heat.
ALARM CONTACTS
The Control Module closes another set of contacts whenever the
water heater is locked out or the power is turned off. This can
be used to turn on an alarm, or signal a Building Management
System that the water heater is down.
WIRING OF THE LEAD/LAG
When wiring the water heaters for Lead/Lag operation, select
one water heater as the Leader water heater. The remaining
water heaters will be designated as Members. See page 58
“Configuration of the Lead/Lag” for a detailed explanation of this
procedure.
Connect the tank sensor to the Leader water heater. For the Lead/
Lag system to work properly the tank sensor must be installed.
The tank sensor should be wired to the low voltage connection
board at the terminals marked for the tank sensor (see Figure
72). The Leader control will use the water temperature at the
tank sensor to control the operation of the Lead/Lag.
Communication between the Leader water heater and the
Member water heaters is accomplished by using shielded, 2-wire
twisted pair communication cable. Connect one of the twisted
pair wires to Lead/Lag terminal A on each of the Low Voltage
Connection boards, and the other wire of the twisted pair to Lead/
Lag terminal B on each of the Low Voltage Connection Boards.
Connect the shield wires to one of the shield terminals on the
Low Voltage Connection Boards (Figure 72). If more than two
water heaters are on the Lead/Lag, daisy chain the wiring from
the Lead/Lag terminals on the second water heater to the Lead/
Lag terminals on the third water heater, then from the third to the
forth, and so on. The connections between heaters can be made
in any order, regardless of the addresses of the water heaters.
Try to keep each cable as short as possible.
DAMPER RELAY
If dampers need to operate when the water heater fires, they can
be controlled by this output. Connect these terminals to a 24 VAC
relay coil, which is wired to operate the dampers (Figure 72).
DAMPER PROVING SWITCH
When the operation of the dampers needs to be verified before
the water heater fires, remove the jumper wire from these
terminals and connect them to the normally open contacts on its
proving switch (Figure 72)
HIGH GAS PRESSURE SWITCH
If a switch is provided to detect excessive gas pressure, remove
the jumper wire from the terminals on the connection board, and
then connect them to its normally closed contacts (Figure 72).
LOW GAS PRESSURE SWITCH
1. If a switch is provided to detect low gas pressure, remove the
jumper wire from the terminals on the connection board and
connect them to its normally open contacts (Figure 72).
2. If both a high and low gas pressure switch are used, connect
their respective contacts in series, and connect them to the
terminals on the connection board (Figure 72).
See Gas Connections section on Page 42 for a detailed
explanation regarding high and low gas pressure switch
operation.
FLOW SWITCH
1. A flow switch is used to guarantee flow through the water
heater before allowing it to fire. The flow switch must be
installed at the water heater outlet.
2. Connect these terminals to the normally open contacts on
the flow switch (Figure 72).
RATE OUTPUT
This output provides a 0 - 10V signal that is proportional to the
firing rate of the water heater. This may be used by a BMS system
to monitor the actual rate of the water heater.
MODBUS
When the optional ModBus interface module is installed, the RS-
485 ModBus cable is connected to these terminals. Use shielded,
2-wire twisted pair cable. If desired, the shield can be connected
to ground by installing a jumper wire between terminals 1 and 3
on connector X5 on the optional ModBus interface module.
