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Installation & Operation Manual
54
11 Operating information
Cascade (continued)
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.
The boiler will fire at its ignition speed and will then modulate
its firing rate to maintain the set point. If the first boiler reaches
100% of its firing rate, the Leader will calculate at what point the
second boiler could fire at 20% of its firing rate. At this point, the
Leader will fire the second boiler on the Cascade. For a new
startup, this would be the first Member boiler. The boiler will
fire at its ignition speed and will then modulate its firing rate to
maintain the set point.
If the set point still cannot be met, the Leader will continue
firing more Members until either the heat demand is met or all
boilers on the Cascade are firing. As the heat demand decreases,
the last boiler on will modulate down to 20% of its firing rate.
Once the demand for that boiler is zero, it will shut down. As the
heat demand decreases further, the second to last boiler will
modulate down and shut off. This will continue until the
demand is satisfied and all boilers are shut off.
DHW, Night Setback, and Ramp Delay operation with
cascade
For 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 to the
terminals on the Low Voltage Connection Board marked for the
DHW Thermostat. 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 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. The boiler
will provide heat for the DHW demand until it is satisfied.
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:
DAY SWITCHING ON SEQUENCE
Day 1 L-M1-M2-M3-M4-M5-M6-M7
Day 1 + 1 hour M1-M2-M3-M4-M5-M6-M7-L
Day 1 + 2 hours M2-M3-M4-M5-M6-M7-L-M1