DIFFERENTIAL (Boil DIFF) (See fig. d)
An on/off heat source such as a boiler must be operated with
a differential to prevent short cycling. This differential is
centered around the Boil TRG temperature
• If boiler supply temperature drops 1/2 of the differential
setting below Boil TRG temperature, the control closes Boiler
contact to fire boiler
• If boiler supply temperature rises 1/2 of the differential
setting above the Boil TRG temperature, the control opens
Boiler contact to turn off boiler
• The SYSTEMpro 311 offers either a fixed or automatic
differential setting
• If AUTO differential is selected, the control automatically
adjusts boiler differential setting under current load
conditions to minimize short cycling
BOILER OPERATION
When the SYSTEMpro 311 notices that boiler operation is
required, Boiler contact terminals (15 and 16) close. While the
Boiler contact is closed, the burner segment in the LCD is
displayed.
BOILER PURGE
After all demands are satisfied, the SYSTEMpro 311 continues
to operate primary pump (P3, terminal 8) for 20 seconds.
• Allows any excess heat to be purged out of boiler after
burner is shut off
• Helps prevent water in the boiler from flashing into steam
after boiler is shut off
• There must not be any motorized valves to restrict water
flow through pump and boiler
81
CONTROL FUNCTION
OVERVIEW
CONTROL FUNCTION OVERVIEW - Section F - Boiler Operation
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