Boiler Parameter Worksheet
Appendix
34
NOTES:
1: No member boiler is allowed to start when the header temperature is greater than the HDR SETPOINT or greater
than the MAX SUPPLY T.
The member boilers are required to modulate back to a lower firing rate when the temperature of the boiler is above
the MAX SUPPLY T minus LOLOAD MOD DLT setting.
2: The modulation will be at a minimum when the condition (Max Supply T
– LoLoad Mod Dlt + 8°F) is reached.
Example: (194 - 10 + 8 = 192)
3. The members will also modulate back when the boiler water temp is within LoLoad Hys Slv of the HDR Setpoint.
4. Each member boiler can detect a low load condition when the member boiler supply temp is greater than MAX
SUPPLY T
– LOLOAD HYS SLV or when the member boiler supply temp is greater than HEADER SETPOINT –
LOLOAD HYS SLV. Once a member detects a low load condition, this information is passed to the master boiler and
the member goes to minimum fire and waits for the LOLOAD WAIT SLV time period to expire. The member boiler
rechecks the low load condition at the end of this time and reports the status to the master. If the low load condition is
still active, the master reduces the amount of active boilers and switches off the member boiler with the low load
condition.
The Master boiler then waits for LOLOAD WAITING time period and re-evaluates the load situation. At the
end of that time, if the low load condition is still detected by another member boiler, the master will shut down that
member boiler. This process repeats in increments of one until no more boilers detect low load (or all the boilers are
off).
Boiler Start Restrictions
When the master requests an additional boiler for cascade operation, two conditions must be satisfied.
Startup Restriction #1
–Alarm Condition
When a boiler is requested for cascade operation, it must be free from alarms. If the requested boiler is in an
alarm state, the master will attempt to request another boiler. If no other boilers are available to start due to
alarm conditions, the active boilers will continue to operate. Once the alarm conditions are corrected, the
boilers will be able to rejoin cascade operation.
Startup Restriction #2 - Minimum Return Temperature
When a boiler is
requested for cascade operation, the return water temperature must exceed the “CSC MIN
RET T” parameter. This parameter is designed to assign priority to condensing boilers and also protect non-
condensing boilers from low return water temperatures.
When
a boiler is successfully requested, the boiler shall energize its circulating pump until the “PRE PMP
PERIOD” timer expires. If at any time during this timer “PRE PMP PERIOD” the return temperature drops
below the “CSC MIN RET T”, the boiler will return to standby. Once this timer expires successfully, the boiler
will operate as normal unless its return temperature drops below “CSC MIN RET T”, at which point the boiler
will return to standby.
In periods of heavy load, it is possible that the active condensing boilers are unable to maintain the header
temperature above “CSC MIN RET T”. The master boiler will continue to request additional boilers in order to
satisfy the load, and eventually a non-condensing boiler will be allowed to start. This non-condensing boiler
will come online at full power until its return temperature exceeds “RET T MAX PWR”. Above this
temperature, the boiler will operate according to its PID settings until its return temperature equals “RET T
MIN PWR”. Above this temperature, the boiler will operate at minimum power until its return temperature
exceeds “CSC MIN RET T” plus “HYST MIN RET T”. Once the return temperature is satisfactory, the boiler
will release to full modulation
