Boiler Parameter Worksheet
Appendix
36
1.8.5.1.1 Power Mode
The cascade system can be configured for two distinct operati
on modes through the master boiler’s “POWER MODE”
parameter.
POWER MODE 0 = Minimum Boilers On
This setting is sometime necessary but ideally less efficient as described below.
When the header temperature drops below “HDR SETPOINT” minus “HYST START BLR” the lead boiler is
requested for cascade operation. Once this boiler is online, it will be PID modulated toward the header setpoint.
If the header temperature remains below “HDR SETPOINT” minus “HYST START BLR”, the master boiler starts
the “WAIT BLR SWITCH ON” timer. When the countdown timer reaches 0:00, an additional boiler is requested
for cascade operation, the timer immediately resets and resumes counting down. This timer “WAIT BLR SWITCH
ON” pauses when the header temperature is between the “HYST START BLR” and “HYST STOP BLR”, also
known as the dead band above and below the “HDR SETPOINT”. If at any time the header temperature drops
below “HDR SETPOINT” minus “HYST START BLR”, the timer resumes its countdown from the last paused time
and will not reset until it reaches 0:00.
Power Mode 0 will attempt to satisfy the load with as few boilers online as possible. When the load only requires
two boilers, both boilers modulate in parallel according to the cascade PID settings. If the load requires three
boilers, the first boiler operates at maximum power while the second and third are PID controlled; modulating in
parallel. If the load requires four boilers, the first two boilers operate at maximum power while the third and forth
boilers are PID controlled; modulating in parallel. Only a maximum of two boilers can be PID controlled at any
time.
If the header temperature exceeds the “HDR SETPOINT” plus “HYST STOP BLR”, the master boiler starts the
“WAIT BLR SWITCH OFF” timer. If at the end of the timer, the header temperature still exceeds the “HDR
SETPOINT” plus “HYST STOP BLR”, the last active boiler will be disabled. When the timer reaches 0:00 and a
boiler is disabled, the timer immediately resets and resumes counting down. This timer pauses when the header
temperature is between the “HYST START BLR” and “HYST STOP BLR”. If at any time the header temperature
exceeds the “HDR SETPOINT” plus “HYST STOP BLR”, the timer resumes it’s countdown from the last paused
time and will not reset until it eventually reaches 0:00.
As boilers are disabled, there can still only be a maximum of 2 PID controlled boilers. This process will continue
until only the lead boiler remains online. If just the lead boiler is online and the header temperature still exceeds
the “HDR SETPOINT” plus “HYST STOP BLR”, the lead boiler will return to standby.
POWER MODE 1 = Maximum Boilers On
This setting is more efficient as all needed boilers modulate in parallel at a lower fire rate see below.
When the header temperature dr
ops below “HDR SETPOINT” minus “HYST START BLR” the lead boiler is
requested for cascade operation. Once this boiler is online, it will be PID modulated toward the header setpoint.
If the header temperature remains below “HDR SETPOINT” minus “HYST START BLR”, the master boiler starts
the “WAIT BLR SWITCH ON” timer. When the countdown timer reaches 0:00, an additional boiler is requested
for cascade operation, the timer immediately resets and resumes counting down. This timer pauses when the
header temper
ature is between the “HYST START BLR” and “HYST STOP BLR”, also known as the dead band
above and below the “HDR SETPOINT”. If at any time the header temperature drops below “HDR SETPOINT”
minus “HYST START BLR”, the timer resumes its countdown from the last paused time and will not reset until it
reaches 0:00.
Each boiler that is brought online will operate to the cascade PID settings stored in the master boiler. Power
Mode 1 will modulate all online boilers to the same power. If a particular boiler is not at the power level as
commanded by the master boiler due to any of the boiler’s internal settings, the power indication will flash
repeatedly on its ENVI display screen. The master boiler will always attempt to equalize the power levels of the
online boilers.
