Crest Audio FBN0751 Service Manual page 24

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Service
The two (2) boilers then modulate at the same rate. As the
calculated load increases further and both boilers ramp up
to 80%, it lowers the rate of the first two (2) boilers to 53%
and brings the next boiler on at 53%. The three (3) boilers
then modulate together. As the calculated load decreases,
the boilers will reach a lower threshold (default = 10%), at
which time the last boiler (the third one in this example)
will turn off and the Cascade will increase the rates of the
remaining boilers to provide the equivalent total output
as before ((3 x 10%) / 2 = 15% in this example). This
parameter can be adjusted by the installer by accessing
parameter J10.
L/L: Lead/Lag
This method is used when it is desired to run the least
number of boilers as possible. When the first boiler reaches
100% and calculated demand is still greater, the Cascade
will bring on boiler number two. At the same time the first
boiler will reduce its firing rate by an amount equal to the
initial firing rate of the second boiler. As the calculated
demand continues to increase, the first boiler will go to
high fire, followed by ramping up the second boiler. If the
calculated demand is still increasing once the second boiler
reaches 100%, the Cascade will bring on boiler number
three and reduce the firing rate of boiler number two by an
amount equal to the initial firing rate of the third boiler.
This sequence will continue until the load is matched or
all boilers are firing at 100%. When the load begins to
decrease, the last boiler to fire will modulate down to low
fire and hold there. As the calculated demand continues to
decrease, the second to the last boiler will modulate down
to low fire. If calculated demand is still decreasing, the last
boiler will shut down and the next to the last boiler will
increase its firing rate to make up the lost BTU's of the last
boiler. If the calculated demand continues to decrease, it
will modulate down to low fire and hold there while the
next previous boiler starts to modulate down, as before.
This will continue until either demand is matched or all
boilers have shut down.
Minimum On/Off Time
In order to prevent units in a Cascade from short cycling,
this parameter defines the minimum ON and OFF time for
each unit. The installer can adjust this time by accessing
parameter J7.
Minimum Next On Time
In order to reduce the risk of temperature overshoot with
a Cascade, this parameter defines the minimum time
delay from starting one unit until the next unit may be
started. The installer can adjust this time delay by accessing
parameter J8.
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Rate % to Switch on Next Boiler
When the Cascade is programmed in the Efficiency
Optimization Mode, the currently running boilers must ramp
up to a certain firing rate before the next boiler in the Cascade
will start. This percentage can be adjusted by accessing
parameter J9.
Rate % to Switch off Last Boiler
When the Cascade is programmed in the Efficiency
Optimization Mode, the last currently running boiler will stop
when its firing rate drops to this value. This percentage can be
adjusted by accessing parameter J10.
Number of Boiler Pumps Always On
When multiple Crest boilers are connected in a Cascade, the
SMART TOUCH control can keep a minimum number of the
boiler pumps running, regardless of how many of the boilers
are firing. This is useful in full flow systems where the system
flow is provided by the individual boiler pumps. This number
can be adjusted by accessing parameter J11.
Redundant Leader
In a Cascade, the Member 1 boiler can be programmed to
assume control of the Cascade if it should lose communication
with the Leader boiler. This feature can be enabled by accessing
parameter J12 with the PC program. Note that this parameter
must be set to YES in both the Leader and Member 1.
For best operation, Member 1 should have its own set of
outdoor, tank (if needed), and system temperature sensors
connected to it.
Do not connect any sensor to more than
CAUTION
one boiler. Doing so will result in the
temperature readings being significantly
lower than the actual temperatures.
Always provide separate sensors for each
boiler.
Legacy Boiler Size Code
The legacy boiler size code parameter is used to determine the
maximum power and priority of legacy boilers (i.e., Power-
fin) in cascade with the Crest Boiler. The default value for
this parameter is 0. When this value is left unchanged, the
SMART TOUCH control will automatically assume that any
member(s) of the Cascade not communicating their size will
be 1,500,000 Btu. The lowest priority will always be given to
these units because the SMART TOUCH control will assume
they are non-condensing boilers. Changing this parameter is
not necessary for Cascade operation. However, the installer
can adjust this code by accessing parameter 4CR using the PC
program. The PC program will calculate the proper size code
based on the information provided.
Service Manual