Cfb 930 And Cfb 910 Control Units - Bosch UT-L 1 Technical Manual

44 | Boiler control and control system
When the burner starts, the boiler circuit pump PK is
switched on. After the burner has shut down, the boiler
circuit pump PK is stopped after a delay. This pump run-
on time can be set with potentiometer P2 to between 30
and 60 minutes for the lead boiler or to 5 minutes
(potentiometer limit) for the lag boiler in a multi boiler
system. The SR actuator for the lag boiler closes.
7.2

CFB 930 and CFB 910 control units

Brief description of possible applications
Fig. 26 CFB 930 and CFB 910 control units
[1] CFB 930 (optional full equipment level);
blue: additional equipment
[2] CFB 910 (standard equipment level);
blue: slots for additional equipment
The CFB 930 and CFB 910 digital control units can
control a floor standing Bosch oil or gas boiler with a
single stage, 2-stage or modulating burner. They also
support operation of dual fuel burners. These control
units may be extended with up to four function modules
to provide an optimum match to an individual heating
system. Multi boiler systems can be controlled with the
CMC 930 strategy module in the CFB 930 control unit.
Boiler safety functions
Boilers and gas condensing boilers with optional boiler
protection functions can be adjusted at the service level
of the Programmer programming unit to safeguard the
operating conditions.
The correct settings in conjunction with the appropriate
plumbing configuration guarantee that the required
boiler operating conditions are maintained.
Burner control
The central module in the control unit control single
stage, 2-stage or modulating burners subject to output.
With dual fuel burners, it can switch between oil and
gas.
They are generally controlled via burner cable stage 1
and burner cable stage 2.
Alternatively the burner can be controlled via a 0-10 V
signal, in which case the burner cable stage 2 is no
longer required.
6 720 807 794 (2013/04)
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6 720 642 347-37.1il
Multi boiler systems
Fitting the CMC 930 function module to the CFB 930
control unit (maximum of two per system) enables up to
eight boilers to be controlled according to a strategy.
One CFB 910 control unit is required per lag boiler.
Special functions for single and multi stage boiler
systems
• Separate boiler curve can be adjusted with third party
control of the consumers
• Control of a boiler circuit pump for systems with
depressurised headers or low-loss headers
• Output-dependent control of a boiler circuit pump via
a 0-10 V signal in conjunction with modulating burners
• Application of a potential-free signal for an external
fault display or for switching between gas and oil
operation in the case of dual fuel burners
Special functions for multi stage boiler systems in
conjunction with the CMC 930 strategy module
• Parallel or serial operation can be set
• Automatic sequence reversal, can be daily, by hours
run, by outside temperature or via a floating contact
• Freely configurable load limit subject to the outside
temperature or via a floating input
• Definable boiler sequences
• Lag boilers can be hydraulically shut off, taking
account of automatic sequence reversal
• Adjustable boiler circuit pump run-on to utilise
residual heat in the lag boilers
• 0-10 V input for external set value hook-up as set
temperature value or output specification (heat
demand) with third party heating circuit control units
• 0-10 V or 0-20 mA output for issuing an external set
temperature value (heat demand) to an overriding
control system (DDC/GLT)
• Indication of status of individual boilers
• Floating output for central fault message
• Floating input for hooking up an external heat meter
• Outside temperature sensor FA (only CFB 930)
• Boiler water temperature sensor FK
• Additional temperature sensor FZ for low loss header
or as return temperature sensor
• Burner cable, stage 2
Boiler safety functions
Heating boiler
• If the minimum boiler water temperature is not
reached, the boiler circuit pump, heating circuit
pumps and cylinder primary pump are shut down and
restarted with a switching differential when the boiler
temperature rises. This boiler protection function is
designated "pump logic". The switching threshold
depends on the burner type and is preset at the
factory.
• The following boiler protection functions are available
to control the operating flow temperature:
– Overriding control of the heating circuit actuators
for single boiler systems:
The heating circuit actuators are closed if the
operating flow temperature is not reached,
independent of the heat demand of the heating
circuits. For this setting, all heating circuits must
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