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General
How the boiler operates
The Knight XL uses an advanced stainless steel heat exchanger
and electronic control module that allows fully condensing
operation. The blower pulls in air and pushes fl ue products
out of the boiler through the heat exchanger and fl ue piping.
The control module regulates blower speed to control the
boiler fi ring rate. The gas valve senses the amount of air
fl owing into the boiler and allows only the right amount of
gas to fl ow.
How the control module operates
The SMART SYSTEM control module receives inputs from
boiler sensors and external devices. The control module
activates and controls the blower and gas valve to regulate
heat input and switches the boiler, Domestic Hot Water
(DHW), and system pumps on and off as needed. The user
programs the module to meet system needs by adjusting
control parameters. These parameters set operating
temperatures and boiler operating modes. Boiler operation
can be based on boiler outlet water temperature, boiler inlet
water temperature, system temperature, a 0 - 10V signal, or
Modbus, depending on the parameter settings.
Control inputs and outputs
Room thermostat
There are three (3) thermostat connections available on this
control. These inputs tell the boiler to provide water for space
heating. Each thermostat connection has its own set point
and outdoor air reset curve. When multiple thermostats have
a call for heat the control will give priority to the demand with
the highest set point.
Example: Assume that both Room Thermostat 1 and Room
Thermostat 2 have a call for heat. RoomThermostat 1 has
a set point of 110°F. Room Thermostat 2 has a set point of
140°F. The boiler will regulate the system temperature to
140°F until Room Thermostat 2 has been satisfi ed. Once
Room Thermostat 2 has been satisifi ed the boiler will provide
110°F water to the system.
0 - 10V input (set point or power)
The Knight XL can be controlled by a Building Management
System (BMS) using a 0 - 10 VDC signal. The control can be
confi gured by the installer to use this signal to either control
set point or fi ring rate.
The Knight XL can also be programmed to accept a call for
heat from a 0 - 10V signal, reference the Knight XL Service
Manual for a detailed explanation of this procedure.
DHW priority
The SMART SYSTEM control allows the connection of a DHW
thermostat or tank sensor to the low voltage connection board.
When a tank sensor is connected, the DHW thermostat input
is ignored.
DHW / space heating (SH) cycling
If a DHW call for heat is received while a space heating call
is in progress and the DHW is in Normal Mode, the control
will start the DHW pump and shut the boiler pump off. The
system pump will remain on. If the space heating call is still
active while the DHW call is in operation, the control will wait
for 30 minutes (time adjustable by installer) then it will switch
back to the space heating demand. There is a timer to switch
from space heating to DHW and a timer to switch from DHW
to space heating. The control will switch back and forth until
one of the heat demands end. This function does not apply to
cascade systems.
Programmable controlling sensor
The control module is programmed to use the outlet sensor
as the control sensor by default. If a system supply sensor is
connected, the control automatically uses it as the control
sensor. The control sensor can be changed by the installer to
the inlet sensor. If the inlet sensor is chosen as the controlling
sensor, it is recommended that the system supply sensor be
installed in the system supply in order to provide the best
control of the inlet temperature.
Anti-cycling
After the burner turns off, the control will delay the next burner
cycle for a set time period (time is adjustable by the installer).
The time delay will be bypassed if the inlet water temperature
drops too far during the delay.
Boiler and system pump control
The boiler pump will run whenever the burner is fi ring, unless
the DHW is programmed for Normal Mode and the boiler is
heating the DHW tank. The boiler pump will run during Freeze
Protection Mode as well. It will continue to run for a short time
after the burner turns off or the Freeze Protection Mode ends.
The system pump will run whenever there is a space heating
call for heat, or the boiler goes into Freeze Protection Mode. It
will continue to run for a short time after the end of the heat
demand or the Freeze Protection Mode. The system pump can
be programmed to run continuously if desired. In either case,
it will not run during outdoor shutdown.
Temperature control
Modulation
The Knight XL is capable of modulating its fi ring rate from a
minimum of 20% to a maximum of 100%. The fi ring rate is
dictated by the call for heat (i.e., space heating or domestic hot
water), the heating load, ramp delay (if enabled), and various
other temperature limitations.
11 Operating information
61
ƽ CAUTION
When multiple temperature loops are
used, thermostatic mixing valves are
required for the protection of any low
temperature loops.
Installation & Operation Manual