Bradford White Brute BNTH Installation And Operation Instructions Manual page 49

Brute
BOILERS AND VOLUME WATER HEATERS
Number of boil-
ers installed
1
2
3
4
5
6
7
8
Figure 38. 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 Figure 37),
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.
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)
Base load value
NA
65%
50%
35%
35%
35%
35%
35%
Figure 37. Lead / Lag Operation, 3 or more boilers
1
Low demand -
The first boiler in
sequence fires at
less than 65%
Demand increases -
Once the first boiler
reaches 65%,
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.
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.
2 3 4 5 6
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