65
11
Operating information
(continued)
Outdoor reset operation, if used
Target temperature with outdoor reset
Th
is feature improves the system’s effi
ciency as the outdoor
temperature warms up.
See the Knight XL Service Manual to change the settings.
Reset curve
Th
e reset curves look at outdoor air temperature and adjusts
the set points.
Cascade
When multiple boilers are installed, they can be wired
together in a cascade sequence. A maximum of eight boilers
can be controlled from a single control. In this application
one boiler would be designated as the Leader control and all
others would be designated as Member controls. Th
e Leader
control can be programmed to use Lead/Lag or Effi
ciency
Optimization control methods.
Once the Leader boiler receives a call for heat from a room
thermostat, BMS, or Modbus, the control will determine what
the set point will be. If outdoor air reset is desired, connect
the outdoor air sensor to the terminals on the Low Voltage
Connection Board on the Leader boiler. Th
e set point will be
calculated based on the programmed reset curve parameters.
See the Knight XL Service Manual to program the reset curve.
If outdoor air reset is not desired, do not connect the outdoor
air sensor. A fi xed temperature set point can be programmed
into the control. See page 59 of this manual to program the
set point.
If the water temperature at the system supply sensor is less
than the set point + the turn-off off set - the off -on diff erential,
then the control will initiate a call for heat on the Cascade
(see the Knight XL Service Manual for an explanation of
the off set and diff erential). Th
e Leader will energize the lead
boiler on the Cascade. For a new startup this will be the
Leader boiler.
DHW, Night Setback, and Ramp Delay operation with
cascade
For normal mode DHW operation any boiler(s) in the Cascade
can be selected to provide heat for a DHW call. Select a boiler
to be designated as the DHW boiler. Connect the DHW
thermostat or sensor to the terminals on the Low Voltage
Connection Board marked for the corresponding device. When
the boiler receives a DHW call, the Leader control will take that
boiler out of the Cascade sequence. If another boiler is available,
the Leader will start it up to take its place.
Th
e DHW boiler will adjust its set point to the programmed
DHW boiler set point and will adjust its fi ring rate to maintain
this. Once the DHW call has been satisfi ed, the Leader control
will place that boiler back into the Cascade sequence.
Switching of the boiler between DHW operation and SH
operation when there is a call for both does not occur in Cascade
Mode.
When DHW is programmed for Zone Mode, connect the DHW
thermostat or tank sensor to the Leader boiler. When a DHW
call is received, the Leader will modulate the entire Cascade to
bring the system supply temperature up to the DHW boiler set
point (if higher).
Night Setback operation of the boilers within the Cascade is
available. Programming of the Night Setback will be done
through the Leader boiler. Refer to the Knight XL Service
manual for information regarding Night Setback.
Ramp Delay operation of the boilers as described in the Knight
XL Service Manual is available when the boilers are part of a
Cascade system.
Sequence of the cascade
To equalize the run time of all boilers on the Cascade, the fi ring
sequence will automatically be changed at set intervals.
Th
e sequence will be changed once every 24 hours. Th
e
switching on/off sequence will be as follows:
TIME
SWITCHING ON SEQUENCE
Start
L-M1-M2-M3-M4-M5-M6-M7
1 hour
M1-M2-M3-M4-M5-M6-M7-L
2 hours
M2-M3-M4-M5-M6-M7-L-M1
If a boiler locks out or is used to heat an indirect DHW tank,
it will automatically be given the lowest priority for the rest of
that 24 hour period.
Low water cutoff protection
1. Th
e SMART SYSTEM control module uses temperature
sensing of both supply and return areas of the heat
exchanger. If the fl ow rate is too low or the outlet
temperature too high, the control module modulates and
shuts the boiler down. Th
is ensures boiler shutdown in
the event of low water or low fl ow conditions.
2. Some codes and jurisdiction may accept these integral
features of the control in lieu of requiring an additional
limit control or low water cutoff . Consult local jurisdiction
to determine. A low water cutoff is available from the
factory (100173646).
Installation & Operation Manual
