WHL-038 Rev. 1.29.16
42
J. Setting Up a Cascaded System
If the boiler is part of a cascaded system the operation is
somewhat different. The control of each boiler in a cascaded
system completes its own power up system check. One of
the boilers in the cascade system is designated as the master
boiler. After the master boiler completes its power up sequence,
it checks the communication bus to see if any other boilers
are present. If other boilers are present, the master control
determines these follower boiler addresses. The master boiler
control will recheck the bus every few seconds as long as it is
powered up to update the status of the connected boilers. The
control in the master boiler processes all heat demands and
dictates which of the follower boilers should light and what
firing rate the followers should try to achieve.
When the master boiler receives a demand for heat, it determines
which boiler is first in the firing sequence and sends that boiler
a command to begin a demand sequence. That boiler will then
begin a demand sequence as described above. Once the boiler
ignites, the master boiler control will increase the firing rate
command to that boiler until the system sensor temperature is
at the set point temperature plus the differential, or that boiler is
at high firing rate. If the command from the master boiler control
gets to the high firing rate of the follower boiler, but the system
sensor is below the required temperature, the master boiler
control will then tell the next boiler in the firing sequence to
begin its demand sequence. The master boiler control will then
begin to ramp up the firing rate command of that boiler. This
process will continue while there is a demand until all boilers in
the cascade system are at high fire or the desired temperature of
the system sensor is reached. If the system sensor temperature
reaches tank set point and differential before all boilers are at
high fire, the master control will modulate the cascade command
signal to maintain the system sensor at set point and differential
until the demand is complete. When the system sensor is equal
to the set point temperature, demand is complete, and the
master boiler control will extinguish all boilers that may be lit.
If the demand decreases, the firing rate command and amount
of boilers lit will decrease exactly opposite as described above.
Whenever the master boiler control needs to fire a follower
boiler, it sends a firing rate command to that boiler. The follower
boiler will respond to the command until its supply sensor
temperature gets to be 5
o
F above the set point temperature plus
the differential, at which point the individual boiler will modulate
on its own so as not to overheat. As a result, it is not uncommon
to see the cascade output at maximum but individual boilers
firing at less than their maximum firing rate.
interval. The control will then be in standby, waiting to process
the next demand for heat.
During this process, the control will extinguish the burner
if it senses a dangerous or unsafe condition. If the control
determines that a dangerous or unsafe condition has occurred,
the control may lock out the boiler and prevent it from igniting
until a maintenance person diagnoses the problem, repairs it,
and resets the control. In the event that the control goes into
lockout, it will show a diagnostic code on the display, illuminate
the LED fault indicator, and close the alarm relay contacts to aid
in recognition of the condition, diagnosis, and repair.
K. Lockout Condition
If any boilers, including the master boiler in the cascade system,
are in a lockout condition, the master control will recognize
the lockout condition and skip over the boiler in the firing
sequence. Each boiler in the cascade system is responsible
for its own safety functions. So, if any individual boiler control
senses an unsafe condition, it will extinguish the burner and, if
necessary, go to a lockout condition. In this way, every boiler
in the system has its individual safety controls intact and
operational, even if the firing of the boiler is under control of
the master boiler.
In the event that the system sensor fails, all boilers in the
system will ignite simultaneously when there is a demand, and
each boiler will individually regulate firing rates to maintain
the master set point temperature (tank set point + installer
#4) at the individual supply sensors built into the boiler. If
this should happen, the master boiler will display an E03 fault
code, indicating that the supply sensor has failed.
L. Cascade System Programming
1. If the boiler is used alone, skip this section.
2. Programming the Master Boiler:
a. Make sure there is no demand for heat being supplied
to the boiler.
b. Apply power to the boiler.
c. Enter the system setting program navigation following
instructions in this manual.
d. Verify that cascade address function 15 is set to 0. This
makes the master boiler address 0. NOTE: The Master
Boiler MUST be addressed as 0.
e. Change CASCADE MODE function 23 to 928 BOILERS.
f. Exit the installer menu.
3. Programming Follower Boilers:
NOTE: READ THE NOTES BELOW BEFORE
PROGRAMMING FOLLOWER BOILERS
•
The master boiler will share its alarm output with the
boiler addressed as 1.
•
If one of the follower boilers has an indirect fired water
heater connected to it, the address of this boiler must
be 2 or greater.
•
It is recommended but not necessary to address boilers
in the order that they are wired.
•
No two boilers can have the same address.
•
It is not required to use all consecutive address
numbers. Example: In a 2 boiler system with an indirect
connected to the follower, the follower address would
be 2 (address 1 is not used).
•
Maximum amount of boilers in a cascaded system is
eight (8).
a. Make sure there is no demand for heat being supplied to
the master boiler.
b. Apply power to the follower boiler you are working on.
c. Enter system settings following instructions in this
manual.
d. Set cascade address parameter 15 to 1 for the first
follower, 2 for the second follower, etc. depending on
which boiler you are programming based on the above
notes. This establishes the boiler as a follower in a cascaded
system and enables data to be transferred as needed for
the system to function at full capability.
e. Change CASCADE MODE Function 23 to 928 BOILERS.
f. Exit the installer menu.