Installation & Operation Manual
56
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 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.
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 Boiler Service
manual for information regarding Night Setback.
Ramp Delay operation of the boilers as described in the
Knight Boiler 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
