MagnaTherm Boilers and Water Heaters
Page 69
Figure 44. 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 65%,
the second boiler
switches on, and
both modulate
together between 20%
and 65% (this can be adjusted up to 20% and
85
%).
Demand increases -
Once the first two
boilers reach 65%,
the third boiler
switches on, and all
boilers modulate together
between 20% 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 21. Base Load Settings
If the Modbus addresses are not
assigned properly, the system could
fail to operate correctly, or it might
operate in an unsafe manner. This
could lead to property damage,
personal injury or death.
•
When the Run sequence is initiated,
the unit with the least amount of
runtime will fire.
• If the heating demand increases so
that the firing rate of that first unit
rises to your unit configurations Base
Load Value
(see Table 21)
, the next
unit 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 units will modulate up or down
together, in reaction to the changes in
demand.
See Figure 42 and Figure 44
Control Settings for Lead Lag System
- Part 1
1. Power up all of the units in the system.
2. In an installation with several units, you must give
each unit a different name, so that the controller
of the Lead unit 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 must be ‘Master
Enabled’ first and then set up address “1,” and the
other units should each be ‘Slave Enabled’ and
have unique Modbus address numbers typically 2
thru X (total number of units)
On each unit, touch the controller icon on
the home screen
.
