CleaverBrooks CFC-500 Operation, Service And Parts Manual page 204

CB FALCON
Table 38. Warm Weather Shutdown (WW-SD) Parameters. (Continued)
Parameter
Warm weather shutdown setpoint Temperature or None
Frost Protection
LL master frost protection is enabled with the LL - Frost
protection enable parameter.
The need for frost protection is actually detected independently
by each slave, which notifies the master whether frost
detection occurred in CH frost detection, and/or its DHW frost
detection, and whether it is severe enough to require burner
firing as well as pump operation. This is done via its BC - Slave
status parameter.
If LL - Frost protection enable is Enable, then the master's LL -
Slave write message, will indicate CH or DHW frost protection
or both as read from each slave's BC - Slave Status. This will
cause any slave pumps which are enabled to follow this status
to turn on without any other action required from the master.
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When warm weather shutdown is Disabled then it has no effect (i.e. the Warm Weather
Shutdown (WW-SD)) status shown on the priority diagram is false).
These two parameters are shared by the stand-alone Falcon control and the LL master and
have the same effect for either control.
If it is enabled then it uses a 4°F (2.2°C) hysteresis:
If WW-SD) is false, then when the Outdoor temperature is above the value provided by Warm
weather shutdown setpoint then:
If Shutdown after demands have ended is selected then any current CH demand that is
present prevents WW-SD) from becoming true; that is if CH demand is false then WW-SD)
becomes true.
Otherwise if Shutdown immediately is selected then WW-SD) becomes true, it immediately
causes CH demand to end.
If WW-SD) is true, then when the Outdoor temperature is below the value provided by Warm
weather shutdown setpoint minus 4°F then WW-SD) becomes false.
When warm weather shutdown is true then:
New occurrences of CH demand is inhibited.
DHW demand is not affected.
Comment
If any slave is indicating CH or DHW frost protection, and
additionally that slave's BC - Slave status register indicates
burner firing is requested then the LL master's frost protection
burner demand will be true.
If the priority scheme allows the master to honor this demand,
then it will fire a single burner (the current lead burner as
specified by the sequencer) at the rate indicated by LL - Frost
protection rate: 0-100%. (100% represents 100% firing of this
boiler, and where 0% or any value less than the boiler's
minimum firing rate represents the minimum firing rate).
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