Bradford White BLMC125NA - Manual (Page 30)

Page 28 Bradford White Corp.
SECTION 9.
Modes of Operation
The Brute Elite control allows the boiler to operate
in many different modes of operation. The mode
must be selected based upon the requirements of the
installation. The following sections describe the basic
operation of the Brute Elite in each of the different
modes. Familiarize yourself with each mode and how
the operation of the boiler varies, depending upon the
installation and inputs the control is monitoring.
9.1 Hydronic Heating Demand
When using the Brute Elite for hydronic heating 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, shifts the 3-way valve position
and begins the ignition process. The ignition process
consists of a prepurge, trial for ignition, and run period.
The prepurge period starts on a call for heat once the fan
RPM reaches a preset level. The trial for ignition period
follows once the start-up RPM of the fan is reached. The
trial for ignition period lasts 4 seconds during which the
direct spark ignition system and gas valve are energized.
At the end of the trial for ignition period the flame signal
is compared with the preset flame threshold value. If
the flame signal is higher than the flame threshold the
Brute Elite enters "run". If the flame signal is below
the threshold the Brute Elite returns to prepurge and
starts the ignition process over. In "run" the Brute Elite
monitors the flame signal, call for heat, safeties, and
water temperatures and modulates as needed between
100% and 20% of rate to satisfy the call for heat.
9.2 Hydronic Heating with Outdoor Reset
Outdoor reset varies the control point setpoint
based on the actual outdoor temperature. The reset
function works as shown in Figure 24 . When the
outdoor air temperature reaches the "high outdoor
temperature setpoint (HOD), the control point setting is
adjusted to the low boiler temperature setpoint (LBT).
When the outdoor air temperature reaches the low
outdoor temperature setpoint (LOD), the control setpoint
is adjusted to the CH/Outlet water setpoint temperature.
HOD, LOD and LBT can be adjusted by accessing
SETUP mode. CH setpoint is adjustable from the USER
menu structure.
9.3 Hydronic Heating Using External
Modulation Control
When using the Brute Elite for hydronic heating
with external modulation control a call for heat must
be supplied to the "T-T" terminal. Once the call is
supplied the control starts the boiler and system pumps
and begins the ignition process. In "run" the Brute Elite
monitors the flame signal, call for heat, safeties, and
NAME FUNCTION DEFAULT
VALUE
CH on Burner demand begins when the 5°F
differential outlet water temperature reaches
"Outlet water temperature setpoint"
minus "CH on differential"
CH off Burner demand ends when the 5°F
differential outlet water temperature reaches
"Outlet water temperature setpoint"
plus "CH off differential"
DHW on Burner demand begins when the 2°F
differential outlet water temperature reaches
"Outlet water temperature setpoint"
minus "DHW on differential"
DHW off Burner demand ends when the 7°F
differential outlet water temperature reaches
"Outlet water temperature setpoint"
plus "DHW off differential"
Pump Operates the pump for the overrun 1
overrun time after the burner demand minute
has ended
High Locks the boiler out when the high 200°F
limit limit temperature is reached
(requires manual reset)
Flame Flame signals lower than the flame 0.8Vdc
threshold threshold interrupt burner operation
Table 12. Default Control Settings.
on when the water temperature reaches 115°F. Set the
hysteresis values to match the boiler to the system
operating characteristics. Setting this value correctly
will help reduce the chance of short cycling.
8.8.5 Lead Lag Base Load Setting
The lead lag system uses a base load setting that is
set through the "setup" menu called "bL". The base load
setting identifies the firing rate that the operating boiler
must achieve before the next boiler in the system is
allowed to operate. The default setting is 50% to avoid
short cycling and operating the boilers at higher, less
efficient, firing rates.