LAARS MagnaTherm MGV - Installation, Operation and Maintenance Instructions - Manual (Page 55)

MagnaTherm Boilers and Water Heaters Page 51
Figure 27. Lead / Lag Operation, 3 or more boilers
Low demand -
The first boiler in
sequence fires at
less than 65%
1 2 3 4
Demand increases -
Once the first boiler
reaches 50%,
the second boiler
switches on, and
both modulate
together between 29%
and 65%
Demand increases -
Once the first two
boilers reach 65%,
the third boiler
switches on, and all
boilers modulate together
between 29% and 65%. This continues as demand increases.
5 6 7 8
Nearing max. demand -
The last boiler becomes
active. Once all boilers
reach 65%, all are
allowed to go over
65%
The Lead/Lag controller will change the firing order of
the burners, based on the run time of each burner.
Number of boilers
installed
Base load value
1 NA
2 65%
3 50%
4 35%
5 35%
6 35%
7 35%
8 35%
Table 15. Base Load Settings
• When the Run sequence is initiated, the
boiler with the least amount of runtime
will fire.
• If the heating demand increases so that
the firing rate of that first boiler rises to
your boiler configurations Base Load
Value (see Table 15), the next boiler in
the sequence will start up and begin firing
at 20 to 35% fan speed (depending on
your configuration). After this, the entire
configuration of boilers will modulate
up or down together, in reaction to the
changes in demand.
See Figure 25 and Figure 27
Control Settings for Lead/Lag System -
Part 1
1. Power up all of the boilers in the system.
2. In an installation with several boilers, you
must give each boiler a different name,
sot that the controller of the Lead/Lag Master can
communicate with the other units. All of the units
come from the factory with a Modbus address of “1,”
so you will need to change some of these addresses.
On each unit, go to the screen for “System ID and
Access,” and enter a unique name.
3. The unit operating as the Lead/Lag Master must be
‘Master Enabled’ first and then set up address “1,” and
the other boilers should each be ‘Slave Enabled’ and
have unique Modbus address numbers typically 2 thru
X (total number of boilers)
On the boilers, touch the controller Icon on the Home
Screen.