General
How the boiler operates
Th
e Knight XL uses an advanced stainless steel heat exchanger
and electronic control module that allows fully condensing
operation. Th
e blower pulls in air and pushes fl ue products
out of the boiler through the heat exchanger and fl ue piping.
Th
e control module regulates blower speed to control the
boiler fi ring rate. Th
e 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
Th
e SMART SYSTEM control module receives inputs from
boiler sensors and external devices. Th
e 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. Th
e user
programs the module to meet system needs by adjusting
control parameters. Th
ese 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
Th
ere are three (3) heat/loop demand connections available
on this control. Th
ese inputs tell the boiler to provide water
for space heating. Each demand connection has its own set
point and outdoor air reset curve. When multiple demands
have a call for heat the control will give priority to the
demand with the highest set point.
Example:
Assume that both heat/loop demand 1 and heat/
loop demand 2 have a call for heat. Demand 1 has a set point
of 110°F. Demand 2 has a set point of 140°F. Th
e boiler will
regulate the system temperature to 140°F until Demand 2 has
been satisfi ed. Once Demand 2 has been satisifi ed the boiler
will provide 110°F water to the system.
SMART SYSTEM Multi-temp loop control
Th
e Knight XL boiler is capable of producing up to three
(3) set point temperatures to meet diff erent space heating
demands. Th
is device controls the temperatures of up to
three (3) separate loops, based on the settings for the three
(3) heat/loop demands (reference Lochinvar kit 100167843).
0 - 10V input (set point or power)
Th
e Knight XL can be controlled by a Building Management
System (BMS) using a 0 - 10 VDC signal. Th
e control can be
confi gured by the installer to use this signal to either control
set point or fi ring rate.
Th
e 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
Th
e 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. When a boiler is programmed for DHW Normal
Mode, the maximum fi ring rate can be limited to match the
input rating of the indirect tank coil.
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 . Th
e system
pump will remain on. For stand-alone boilers, 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. Th
ere is
a timer to switch from space heating to DHW and a timer to
switch from DHW to space heating. Th
e control will switch
back and forth until one of the heat demands end. Th
is function
does not apply to cascade systems.
Programmable controlling sensor
Th
e 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. For stand-alone boilers, 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
Aft er the burner turns off , the control will delay the next burner
cycle for a set time period (time is adjustable by the installer).
Th
e time delay will be bypassed if the inlet water temperature
drops too far during the delay.
Boiler and system pump control
Th
e 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. Th
e boiler pump will run during Freeze
Protection Mode as well. It will continue to run for a short time
aft er the burner turns off or the Freeze Protection Mode ends.
Th
e system pump will run whenever there is a space heating call
for heat, or the boiler goes into Freeze Protection Mode. It may
be programmed to run during a DHW call for heat when the
DHW is programmed for Zone Mode. It will continue to run
for a short time aft er the end of the heat demand or the Freeze
Protection Mode. Th
e system pump can be programmed to run
continuously if desired, except during outdoor shutdown and/
or a DHW call for heat.
11
Operating information
62
CAUTION
When multiple temperature loops are
used, mixing valves are required for the
protection of any low temperature loops.
Installation & Operation Manual
