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Installation & Operation Manual
11 Operating information
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.
The DHW boiler will adjust its set point to the programmed
DHW boiler set point and will adjust its firing rate to maintain
this. Once the DHW call has been satisfied, 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 Wall Mount
Service manual for information regarding Night Setback.
Ramp Delay operation of the boilers as described in the Knight
Wall Mount Service Manual is not active 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 firing
sequence will automatically be changed at set intervals.
For the first 24 hours after initializing the Cascade, the sequence
will be changed every hour. After that the sequence will be
changed once every 24 hours. The 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..
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. The Leader
control can be programmed to use Lead/Lag or Efficiency
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. The set point will be
calculated based on the programmed reset curve parameters.
See the Knight Wall Mount Service Manual to program the
reset curve. If outdoor air reset is not desired, do not connect
the outdoor air sensor. A fixed temperature set point can be
programmed into the control. See page 61 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 offset - the off-on
differential, then the control will initiate a call for heat on
the Cascade (see the Knight Wall Mount Service Manual for
an explanation of the offset and differential). The Leader will
energize the lead boiler on the Cascade. For a new startup this
will be the Leader boiler.
Low water cutoff protection
1. The SMART SYSTEM control module uses temperature
sensing of both supply and return areas of the heat
exchanger. If the flow rate is too low or the outlet
temperature too high, the control module modulates and
shuts the boiler down. This ensures boiler shutdown in
the event of low water or low flow 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 (WTR20009).
Outdoor reset operation, if used
Target temperature with outdoor reset
This feature improves the system’s efficiency as the outdoor
temperature warms up.
See the Knight Wall Mount Service Manual to change the
settings.
Reset curve
The reset curve looks at outdoor air temperature and adjusts
the set point.