SG Series Boilers – Installation and Service Manual
15
1.7.1 BC-1 CONTROLLER OPERATION
When the controller is powered, the controller enters the operating mode if there are no sensor or high
limit errors present. The user should select one of the following modes from the controller adjust menu:
Mode 1 - Setpoint operation using parallel piping: Operates boiler stages to maintain fixed
temperature at boiler outlet sensor when a heat demand is present.
Mode 2 - Setpoint operation using primary/secondary piping: Operates boiler stages to maintain
fixed temperature at boiler supply sensor when a heat demand is present.
Mode 3 - Dedicated DHW Generation: Operates boiler stages to maintain fixed temperature at the
boiler outlet sensor when an internal demand for DHW is generated based on the DHW sensor. An
indirect hot water tank must be used to isolate the boiler from an open system.
Mode 4 - Outdoor reset with reset override using parallel piping: Operates stages to maintain an
outdoor reset temperature at the boiler outlet sensor. When there is a call for “reset override” from
the DHW aquastat (i.e. ST&R is closed), the control operates the stages to maintain a setpoint
temperature at the boiler outlet sensor. If both heat demand and setpoint DHW demand are present
at the same time, the controller targets the higher of the two requirements.
Mode 5 - Outdoor reset with reset override using primary/secondary piping: Operates stages to
maintain an outdoor reset temperature at the boiler supply sensor. When there is a call for “reset
override” from the DHW aquastat (i.e. ST&R is closed), the control operates the stages to maintain a
setpoint temperature at the boiler supply sensor. If both heat demand and setpoint DHW demand are
present at the same time, the controller targets the higher of the two requirements.
Mode 6 – External boiler control: It is not necessary to use Mode 6 since Direct Digital Control
(DDC) terminals have been provided on terminal block TB1. The DDC terminals may be used for
connecting a boiler or multiple boilers to an external boiler control or an energy management system
(EMS). See boiler wiring diagram for connection details.
When there is a heat demand or DHW demand the controller will switch on the system pump. If the
sensor is not satisfied, the controller will switch stages on, in sequence, based on PID logic (proportional,
integral, derivative). The controller continuously monitors the sensors and examines the difference
between the target temperature and the sensor temperature. Depending on the difference in temperature
(proportional), the time (integral), and how fast or slow the temperature is changing (derivative), it will
determine when to switch a stage on or off. This feature prevents "short cycling", which can quickly wear
out components and cause rapid temperature fluctuations.
The heating routine will operate until the water temperature reaches the user-defined temperature setting.
Once reached, the control will automatically cycle the stage(s) of the boiler on or off, as necessary, to
maintain the supply water temperature. The required number of stages which are activated is determined
by the controller. After the call for heat has been satisfied, the stage(s) of the boiler will switch off, in
sequence, followed by the pump.
1.7.2 RESET OVERRIDE
WARNING
If both Heat Demand and Setpoint DHW Demand are present at the same time, the controller
targets the higher temperature of the two requirements. This may result in higher than intended
water temperatures in either space heating loop or domestic hot water (DHW) heating loop.
Use pipe rated for use at the highest possible water temperature.
The BC-1 Controller has one pump relay which is normally open and will close (i.e. pump energized)
when either a Heat Demand or Setpoint DHW Demand is present. When using Reset Override, a
switching external pump relay (e.g. tekmar Relay 003) should be utilized to stop hot water flow to the
space heating loop (e.g. radiant in-floor) and redirect it to the DHW heating loop during a Setpoint DHW
Demand. See Figure 4 and Figure 5.
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