Hydronic Heating Using External Modulation Control - Laars NEOTHERM NTH Installation And Operation Instructions Manual

N T Boilers and Water heaters
eo herm
Figure 40 - Lead-Lag / Cascading Wiring Connections
Wiring Connections for Lead/Lag -
Now you can make the Modbus wiring connections
between the units. The controller in each boiler includes
two wiring terminals for the Modbus system, labeled
"MB1" and "MB2." MB1 has the wiring connections to
the User Interface display on each unit, and MB2 is used
to communicate with the other boilers in the Lead/Lag
system. See Fig. 40.
To reach the controller, open the cabinet of the boiler by
removing the plastic bezel.
The wiring from the controller on the first boiler runs to
the controller on the next boiler. Use 22 AWG or thicker
shielded twisted-pair wire with drain. Two twisted pairs
or three conductors are needed. Wire A on MB2 of Boiler
1 must be connected to A on MB2 of Boiler 2, wire B on
Boiler 1 goes to B on Boiler 2, and wire C on Boiler 1
goes to C on Boiler 2. Repeat this wiring for any other
boilers in the system. Connect all of the drain wires and
ground the drain wire on one end of the assembly only.
Control Settings for Lead/Lag System - Part 2
1. On the Lead/Lag Master, set the setpoint used by the Lead/
Lag system.
How to get there: From the "Home" screen, press "I" to
go to "Info/Install." Choose "Advanced Setup," then go
to "Lead/ Lag Configuration." Select "Lead Lag Master
Configuration," and go to the line for "Setpoint."
2. On the Lead/Lag Master, set the Base Load to match
the number of boilers in the system. We mentioned the
Base Load setting in the explanation of the "Lead/Lag
Modulation Cycle." Whenever the heating demand causes
the active burner(s) to run faster than the Base Load value,
the Lead/Lag system will put an additional burner on line.
The Base Load value depends on the number of boilers in
the system:
Boiler 1 Boiler 2
MB 1
MB 2 MB 1 MB 2
A B C A B C A B C A B C
User User
interface interface
Boiler 3 Boiler 4
MB 2
MB 1 MB 2
MB 1
A B C A B C A B C A B C
User User
interface interface
Note that you only need to enter the Base Load value on the
Lead/Lag Master.
How to get there: From the "Home" screen, press "I" to
go to "Info/Install." Choose "Advanced Setup," then go
to "Lead/ Lag Configuration." Select "Lead Lag Master
Configuration." Go to the line for "Base Load Common
Rate."
8C.9 Hydronic Heating Using External
Modulation Control -
About External Control -
When the NeoTherm is used for hydronic heating with
external modulation control, a call for heat must be supplied
to the "T-T or Interlock" terminal. Once the call is supplied
the control starts the Boiler and System pumps and begins the
ignition process. Once in Run, the NeoTherm monitors the
flame signal, call for heat, safeties, and water temperatures.
The boiler setpoint is used to limit the maximum water
temperature leaving the boiler only. The modulation rate
is controlled by a 4-20mA signal supplied by an external
control. (This can also be 0-10Vdc using a converter - Laars
part number CA006100.) When setting up a system using an
external control, take care to set Anti-Short Cycle feature to
prevent "hunting " and possible premature component failure.
Connections for External Control -
Connect the 4-20mA signal from an external control or
building automation system to terminal block 7 (TB7) in the
control panel. The connections are labeled Remote Analog
Input. When making the connections, follow the polarity
designations shown on the label.
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