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8 Operating information
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 Outdoor Knight Boiler 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 37 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
Outdoor Knight Boiler 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.
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.
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 Outdoor Knight Boiler
Service Manual for information regarding Night Setback.
Ramp Delay operation of the boilers as described in the
Outdoor Knight Boiler 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
firing sequence will automatically be changed at set intervals.
During the first 24 hours of operation, the sequence will
change every hour. After that, the sequence will change 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.
Outdoor reset operation
Target temperature with outdoor reset
This feature improves the system's efficiency by decreasing set
point as the outdoor temperature warms up. Energy Efficiency
Standards require the use of a control that automatically adjusts
set point in relation to heat demand. In the absence of an
external energy management system, this feature MUST BE
used.
See the Outdoor Knight Boiler Service Manual to change the
settings.
Reset curve
The reset curve looks at outdoor air temperature and adjusts
the set point in relation to heat demand.
Outdoor Knight Boiler Installation & Operation Manual