Knight 100 Series, Service Manual

Page: 9 / 52

9
Service Manual
1
Service
(continued)
Control inputs and outputs
Temperature control and protection
Modulation
The boiler will modulate its firing rate to satisfy heat
demand. The firing rate is dictated by a space heating
or DHW call for heat, the heating load, ramp delay, and
various other temperature limitations.
Target Operating Temperature
The control module regulates the boiler firing rate to
achieve a target temperature set point.
High Limit Operations
The boiler is equipped with adjustable automatic reset
(maximum set point 210°F) high limits. When the outlet
temperature exceeds the automatic reset set point, the
boiler shuts down until the outlet water temperature cools
10° below set point and a 60 second timer has expired. If
the outlet temperature continues to increase to the manual
reset set point, the boiler will shut down until the control
is reset.
Low Water Cutoff Protection
The control uses inlet and outlet water temperature sensors
to monitor flow and temperature rise across the heat
exchanger. If the flow is too low or the outlet temperature
too high, the control will modulate and shut down the
boiler.
Gradient Limiting
If the boiler outlet water temperature is rising too quickly,
the control will reduce its firing rate to the lowest setting.
Flame Current Support
When the boiler is firing at minimum rate, the control will
increase the firing rate if the flame signal drops too low.
Outlet Temperature Limiting
When the outlet temperature exceeds 185°F the control will
reduce the fan speed. If the temperature exceeds 195°F, the
unit will shut down until the temperature drops.
Flue Temperature Limiting
The control will reduce the fan speed if the flue temperature
exceeds 215°F, and shut down if the temperature exceeds
225°F. The boiler will restart once the temperature has
dropped 25°F and the minimum off time has expired.
Temperature Rise Limiting
If the temperature difference between the inlet and outlet
sensor exceeds 55°F, the control will reduce the fan speed.
If the difference exceeds 60°F, the control will shut the
unit down until the difference drops below 55°F and the
minimum off time has expired.
Freeze Protection
The control module provides freeze protection by operating the
boiler and system pump constantly when the water temperature
drops below 45°F. If the temperature drops below 37°F, the
control will fire the boiler until the temperature rises.
Field Wiring
Heat / Loop Demand
Room thermostat connections available for space heating. The
SMART SYSTEM Multi-Temp Loop Control can be used to
control the temperatures of up to three (3) separate loops.
DHW Tank Sensor and Tank Thermostat
The boiler can be programmed for DHW priority when a
DHW thermostat or tank sensor is used. When there is a DHW
and space heating call for heat, the control can be programmed
to cycle between the two demands for a specified time period.
DHW Recirculation Pump Sensor and Relay
Used to control a DHW recirculation pump.
System Sensor
When installed, the control will adjust the boiler firing rate to
maintain the system supply temperature set point.
0-10V System Pump In
When a variable speed system pump is installed in the primary
loop, the control can use a 0-10V signal from the pump speed
control to anticipate changes in building heat load.
0-10V Boiler Pump Out
When connected to a variable speed circulator, the control can
use a 0-10V signal to adjust the speed in order to maintain a
minimum ΔT across the heat exchanger.
Outdoor Air Sensor
The control will adjust boiler set point according to the
outdoor air temperature.
High/Low Gas Pressure Switch
Connect to a pressure switch to detect excessive or low gas
pressure.
Flow Switch
Install at the boiler outlet to verify flow before the boiler fires.
Low water cutoff (LWCO)
Required by some jurisdictions to ensure adequate water flow
through the boiler.
AUX (Louver) Proving Switch
Verifies operation of louvers or auxiliary equipment before
the boiler fires. A custom name can be configured through the
SMART SYSTEM display.