Service manual

MSE Series Electric Boilers – Installation and Service Manual
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5.3 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: Operates boiler stages to maintain fixed temperature at boiler
outlet sensor when a heat demand is present.
Mode 3 - Dedicated DHW Generation: Operates boiler stages to maintain tank temperature at
the SD sensor. An indirect hot water tank must be used.
Mode 4 - Outdoor reset with reset override: 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.
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 on additional stage(s), in sequence, and based on PID
(proportional, integral, derivative) logic. 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 contactors 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.
5.4 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 6 and Figure 7.
Figure 6 – Typical piping arrangement of system components in Mode 4
2S
1S
1T1T
1A
1Pump
2Pump
MM
MODE 4 ONLY
(Outdoor reset and reset override)
S1 = Boiler Outlet Sensor 071
S2 = Boiler Inlet Sensor 071
Pump1 = Boiler Pump
Pump2 = DHW Pump
A1 = DHW Aquastat
T1 = Thermostat