Temperature Control - Lochinvar Knight WHN055 Installation & Operation Manual

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Operating information

Temperature control

Modulation
The Knight wall mount boiler is capable of modulating its
firing rate from a minimum of 20% to a maximum of 100%.
The firing 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.
Ramp delay
For systems with lower flow, the SMART SYSTEM can limit
the firing rate (when enabled) when a space heating call for
heat starts, or when switching from a DHW call for heat to a
space heating call for heat. There are six (6) limits that can be
programmed, as well as six (6) time intervals corresponding
to each limit. The sixth limit will also limit the firing rate for
the rest of the call for heat.
Gradient limiting
If during operation of the boiler the outlet water temperature
is rising too quickly, the control will reduce the firing rate to
its lowest setting.
Outdoor air reset
With the outdoor air sensor connected, the control module
will calculate the set points of the three (3) space heating
demands based on the programmed reset curves.
installer can change the slope of the reset curves by several
adjustable parameters. The user can limit the maximum set
point for the system using the space heating set points.
Boost function
If outdoor air reset is active, and any space heating demand
has been active continuously for a set period of time (time
adjustable by installer) and there has been no DHW demands,
the control will increase the set point of that demand by a
fixed number of degrees (adjustable by installer). This process
will continue until the space heating demand ends, the set
point reaches the programmed set point or a maximum of
20 increases has occurred. Once the system heat demand is
satisfied, the set point will revert to the value determined by
the reset curve.
Night setback
The controller may be programmed to reduce the space
heating and DHW set points during certain times each week.
Seven different start and stop times may be programmed for
the space heating setback and seven start and stop times for
the DHW setback. Any night setback scheduled within the
next seven (7) days can be temporarily bypassed if desired.
Flame current support
To prevent nuisance shutdowns when the boiler is firing at
minimum rates, the control will increase the firing rate when
the flame signal drops too low.
(continued)
Protection features
Outlet temperature, flue temperature, and temperature
rise limiting
The outlet temperature is monitored by the boiler outlet
temperature sensor.
185°F, the unit will reduce the fan speed. If the outlet water
temperature exceeds 195°F the control will shut the unit down
until it cools off.
The control module monitors the flue temperature by a sensor
located in the flue exhaust. If the flue temperature exceeds
215°F the control will reduce the maximum fan speed. If
the flue temperature exceeds 240°F the control will shut the
unit down. The unit will restart automatically once the flue
temperature drops 25°F and the minimum off time has expired.
The control monitors the temperature difference between the
inlet and the outlet sensor. If this difference exceeds 55°F the
control will reduce the maximum fan speed. If the temperature
difference exceeds 60°F the control will shut the unit down. The
unit will restart automatically once the temperature difference
has dropped below 55°F and the minimum off time has expired.
Freeze protection
DO NOT install the boiler in a room likely to freeze.
The
The following integral feature of the SMART SYSTEM control
module provides some protection for the boiler only -- not for
the system.
• The SMART SYSTEM control module provides
freeze-up protection as follows when the boiler
water temperature drops below 45°F:
• Below 45°F, the boiler and system pumps operate
constantly.
• Below 37°F, the boiler turns on and runs at 20% of rate.
• Boiler and pumps turn off if boiler water
temperature rises above 45°F.
• Lower temperatures may be programmed for
systems with anti-freeze solutions (see the Knight Wall
Mount Service Manual.
When
NOTICE
are maintained below the dew point,
condensation will form on the inside of the
boiler jacket causing some internal sheet
metal components to rust.
This feature of the SMART SYSTEM control
CAUTION
module does not eliminate the possibility
of freezing.
use recognized design, installation and
maintenance practice to prevent freeze
potential for the boiler and system.
Installation & Operation Manual
When the outlet temperature exceeds
system return
The installation must still
temperatures
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